4A-G Crankshaft, Front Pulley & Flywheel

Complied and written by Richard White, submitted 1/05

 

4A-G Crank

The 4A-G crank is by all appearance a high performance piece of hardware. Unlike many production crankshafts which are nodular cast iron, the 4A-G is forged.  It is a forged carbon steel, five main bearing, fully counter balanced affair.  Each journal is cross drilled for 360-degree supply of oil to the connecting rod bearings, and each hole is chamfered to aid in oil delivery. An additional feature of the 4A-G crank is that each main bearing journal has rolled fillets to improve fatigue strength.

 

The transition between the main bearing surface and the crank counter weight and rod journal is subjected to very high torsion forces.   Compressing the material around the transition, increases the strength and, therefore, the life of the crank.  Other performance features include the use of a roller bearing (Toyota p/n 90363-12003) for the transmission pilot shaft (T50 Transmission only) and the use of eight 10mm fly-wheel bolts rather than the usual six that many engines of this size would normally have.  This is contrary to Toyota’s illustrations in their own repair manuals typically showing six.  And because there are no dowel pins to locate the flywheel position Toyota uses close fitting shoulder bolts.  If the flywheel and crankshaft are fitted and torqued properly, all the stress (compression/friction) should be at the interface between the crankshaft and flywheel and the bolt’s shear strength is only needed if something in the system has failed.  Rarely do you want a design that uses a fastener in a single shear plane.  Bolts are at their best in tension.

 

The eight fly wheel bolts add considerably to the strength of the assembly and the roller bearing pilot bearing reduces parasitic frictional losses between the input shaft of the transmission (T50) and the crank.  It also aids in keeping the mis-alignment between the transmission and engine to a minimum while supporting the end of the transmission input shaft, reducing the likelihood of bending it.  However, it is curious that the crankshafts for front wheel drive transmissions (transverse mounted configurations) do not have a pilot bearing, even though the crank shaft has a machined pocket for it.

 

 

For those interested in additional strength and durability, ARP (pictured on the bottom) offers a replacement for the Toyota 4A-G fly wheel bolts.  It is a 10mm x 1.25 bolt, 12 point (half inch head); rated at 190ksi tensile strength, part number 203-2802.   The ARP bolts are torqued to 58ft-lbs. (with ARP Moly Assy. Lube)(85ft-lbs. with 30wt motor oil) as compared to the stock 54ft-lbs.  Before using the ARP bolt it is necessary to verify that the fly wheel holes have adequate chamfer to clear the radius under the head of each bolt.  The threads should also be clean and the hole free from debris.

 

Even though all 4A-G crankshafts have the same high strength features, there are two variations.  The early model has the small rod journal diameters (40mm)(p/n: 13401-16010) and the later models have the large rod journals (42mm)( p/n: 13401-16020).  And other than that, they are indistinguishable. 

 

It is interesting to note that all the late model, large crank pin cranks-shafts are identical, i.e., same Toyota part numbers.  However in reviewing the maintenance manuals, Toyota calls out much tighter inspection tolerances in the last generation 20 valve.  The obvious reason would be to keep parasitic friction and vibrations to a minimum due to the difference in max engine speed that the 20 valve engines were allowed to turn versus the 16 valve ones.

 

The 20 valve engine manual specifies that the crank be straight to 0.03mm.  Each main journal should be within 47.982~48.010mm (1.8891~1.8898inch) diameter, taper and out of round to within 0.005mm (0.0002inch), and run out to within 0.03mm (0.0012inch) max.  By comparison, the tolerances specified in the other Toyota manuals for the late model 16 valve engines are larger. Each main journal should be within 47.982~48.010mm (1.8891~1.8898inch) diameter, taper and out of round to within 0.02mm (0.0008inch), and run out to within 0.06mm (0.0024inch) max.

 

As an additional note, TRD specifies its Group A and N2 crankshafts have a crankshaft “bend” of less than 0.01mm.

 

When rebuilding the engine, the crank, like the block, should be thoroughly cleaned and inspected.  Each throw phased checked. It should be flat, 180 degrees.  And each bearing journal should not only be visually inspected but felt with the finger nail for any ‘grooves’ or deep scratches.   There should be none.

 

During disassembly, one should (must) keep all the matching parts together and labeled, identifying its location.  The same goes for the used bearings.  By keeping the old bearings together with its bearing cap one can inspect and note the OEM Bearing size number printed on the back side for easier replacement.  However, if one of the numbered markings can not be determine, the correct bearing can be selected by adding together the numbers imprinted on the cylinder block and crankshaft, then select the bearing with the same number as the total.  There are 5 sizes of standard bearings, marked 1, 2, 3, 4, and 5.  Please note, the small journal cranks had the bearing size stamped only on the block.

 

	Stamped Number Mark
Cylinder Block #	1			2			3
Crankshaft #	0	1	2	0	1	2	0	1	2
Select Bearing #	1	2	3	2	3	4	3	4	5

 

As an example (see colored in blue) if the stamped number in the first position on the block is a 2 and the stamped number in the second position on the crank is a 2 you would select a #4 bearing for the number 2 main.

 

After cleaning the crankshaft, the crank should be crack tested.  A crankshaft destined for severe duty must be free of flaws.  After Magnaflux crack testing, the crank should be fully de-magnetized, as any residual magnetism after Magnaflux testing will attract ferrous metal particles to the area, which would soon wipe out a bearing.

 

A quick method to check the crank can be done with the crank mounted on top of the main bearing caps, e.g., the crank sitting on the main bearing saddles.  With a cleaned crankshaft and main bearings, the crank can be checked for straightness by first re-installing the crank and all the bearing shells in the block.  All bearing surfaces must be coated with light machine oil.  The main bolts (or studs if up graded) should also be lubricated and torqued to specification.  If the crank turns freely by hand (very little effort), it is straight enough for heavy-duty use. 

 

A more through inspection would require the crank be checked on a lathe and spun to ensure that the pilot bearing is concentric with the centerline of the crank, and the flywheel mounting flange is perpendicular to the crank centerline.  A large variance in either area is rare, but if it exists, it is nearly impossible to correct.  An out of center pilot bearing and/or a non perpendicular flywheel mounting flange would cause large uncorrectable imbalances and is abusive to the clutch.

 

An often over looked inspection is that of End play or Thrust clearance.  Toyota specifies it to be between 0.020~0.220mm (0.0008 ~ 0.0087inch).  Moreover, it is recommended that you check endplay before final assembly of the engine, after it is assembled and after the engine is bolted to the transmission.  It is important to verify that the input shaft of the transmission is not bottoming out against the crankshaft, thus eliminating endplay in the engine, resulting in premature wear in the thrust bearings and causing an endless amount of speculation about the cause.

 

It is important that all the checking and inspection of the crank be done early in the inspection and pre-assembly re-building process.  Gathering and using this information will allow one to build a high performance 4A-G engine and most importantly insure its longevity.  It makes no sense to spend a lot of money preparing the crank only to learn that you can not use it because it was cooked, bent, damaged, etc.

 

Though many engine builders find little modification is needed with a 4A-G crankshaft that will be used in a high performance application, there are several recommendations that have been made.  With the journals protected with several layers of duct tape, all burrs should be removed and the crank polished.  This includes the journals too.  This eliminates stress risers that could lead to failure of the crank.  The duct tape is inexpensive and protects the bearing surfaces against nicks in a journal while grinding.

 

Toyota quality control is quite good as you will rarely see burrs around the oiling holes.  However the oil holes should be brushed clean with a 22~25 caliber brush (0.22 ~ 0.25inch dia). 

 

Please note, it is ideal to remove the oil plugs that have been pressed and staked in place to block off the cross-drilled oil way and replace them with a threaded plug.  However a word of warning, the ball bearing type plug and crank are extremely hard and grinding or milling will be necessary to remove them for a thorough cleaning of the oil way that would otherwise not be possible, i.e., accessible.  Also, care should be exercised in tapping the threads into the crankshaft.  The opening to the oil hole is not usually square or perpendicular to the surface and it is quite easy to mis-guide the tap and possibly break it.  A circumstance you should avoid.

 

Lightening the crank can be beneficial in removing mass and lowing inertia for better engine response and reducing bearing loads.  Cleaning up the counter weights smoothes the surface and reduces the total “wetted” surface area where oil will cling.  The resulting effect reduces the rotating weight and puts the oil back in the sump where it belongs.   However, the amount of weight removed from the crankshaft should be planned for, and balanced with the weight of the rods and pistons (and other assorted fasteners, e.g., pin, rings, bolts, etc.)

 

The term “knife edging” of the counterweights refers to reducing the mass of the counter weight on an angle rather than keeping a straight cut.  The idea is to reduce weight, lower the inertia and reduce aerodynamic drag as the crank tries to move/rotate through the crankcase atmosphere, enabling the crank to speed up more quickly.  There is little aerodynamic benefit with “knife edging” a crank that will be used in a dry sump system.  A good dry sump system pulls a vacuum in the crankcase.  With such a system, the counter weights would have less opportunity to impact the thick oil vapor environment when it is spinning.  Never the less, reducing the crank’s mass and reducing the ‘wetted’ surface area is always a benefit of a high performance crankshaft.

 

To assist in the smooth operation of the motor and to reduce bearing wear, the crankshaft should be dynamically balanced.  This will reduce harmonic loading and vibration that any imbalance would cause.  However because of the physical nature of the four stroke, inline four-cylinder configuration, ultimate balancing can not be achieved to the next, or second harmonic order, like a 60 degree V12, inline 6 or a boxer four.  Moreover, unless one has access to a machine that electronically balances the crankshaft, assistance should be sought to properly balance the crank along with the intended components that will be used on the engine, e.g., front pulley, rods, pistons, rings, Fly Wheel and fasteners.  TRD recommend the crankshaft and flywheel both be balanced separately and together to a balance torque of less than 10g-cm.

 

There are a couple of different techniques that have been used in balancing crankshafts.  Typically, material is drilled out of the circumference of the crank’s counter weight.  Another way would be to angle cut (like knife edging) the edges of the counter weights.  This technique is much more difficult and time consuming. 

 

Adding weight can be done by adding (pressing) heavy metal into a similar drilled hole.  However, this is not recommended, since at high speeds the centripetal forces could pull the plug out.  It is recommended to press the heavy metal plug into the side of the crank’s counter weight.  Another nice, but expensive balancing technique is to weld over the “lightening” holes and grind/polish them flush with the surface. This keeps the “wetted” surface area down, keeping oil clinging to the crank to a minimum and allows for better aerodynamics.

 

The last operation done to the crank should be to micro polish the main and rod journals.  Small scratches in the journal will cut into the bearing and shorten its life.  A polished surface insures maximum ‘rubbing’ area while minimizing any cutting action a rough surface would have.  Another benefit is the elimination of a possible stress site where a crack could start and destroy the crank.

 

One thing that is not recommended for an OEM 4A-G crankshaft is the application of any form of heat treating.  Heat treating could change the attributes that Toyota has designed into their crank. 

 

But as an interesting side note, most production cranks destined for performance work are heat treated.  The common form of heat treating is Tufftriding. Contrary to popular opinion, it does not increase the core strength of the crank.  The Tuftride bath, composed primarily of cyanide and cyanate compounds, that releases specific quantities of carbon and nitrogen in the presence of ferrous materials such as cast iron and alloy steel.  Nitrogen is more soluble than carbon in these metals and diffuses into the surface on the crank, while the carbon forms iron carbide particle at or near the surface.  These particles act as nuclei, precipitating some of the diffused nitrogen to form a tough compound zone of carbon-bearing epsilon iron nitride.

 

At the surface is a compound zone (0.0003 ~ 0.0005” deep) that is tough and very resistant to wear, galling, seizing and corrosion.   Below the surface (0.0008 ~ 0.0014”) is an underlying nitrogen diffusion zone.  This zone is responsible for improved fatigue properties.  The nitrogen, in solid solution, prevents incipient cracks from becoming fatigue failures.

 

In any case it is not recommended to Nitride, Tuffride, or perform other heat treatments to the OEM crank.  The strength of the rolled fillets will be lost and the possibility of warping the crank is a risk that would result in an additional straightening process.

 

A word of warning, if the crank is to be stored for any length of time outside the engine, the crank is easily susceptible to corrosion, i.e., rust, and must be protected from moisture.  The author has found a marine product, Boeshield, to be an improvement over other similar produces like WD-40.  However, the use of WD-40 or any other corrosion inhibiting coating is superior to using none at all.   The idea is to keep moisture and air away from the crankshaft surface.

 

For those interested in using or stroking the 4A-G crank a word of caution is in order.  The 4A-G block is only capable of accepting something less than 83mm (stroke) and at that, requires grinding on the inside of the block, at the bottom of the cylinders to obtain the necessary clearances between the block and the shoulders of the connecting rod and/or connecting rod bolts. 

 

An old hot rodder’s trick was (is) to “weld up” the crank throws and re-grind the connecting rod journals.  This process is highly dependent on the skill of the welder to eliminate any inclusions or voids in the welding and the machinist to index and properly grind the journal with the proper fillet radii and run-out measurements. For a moderate increase in street performance this may be acceptable, but for an all out competition engine, it would not.  The weld material and crank will inevitably not have the same molecular make up, resulting in a different grain structure, i.e., grain boundaries.  These molecular structures will not be in alignment.  Even though you can not see the grain boundaries with the naked eye, they can be viewed with a micro-scope if the crank was cross sectioned and the welded area polished and stained.  Moreover, grain boundaries create weak areas in the metallurgy where stress concentrations will form and if the crank is strained beyond its capabilities, will (could) fail from fatigue.

 

The only acceptable standard for a competition engine is a crank machined from a forged billet. These are the most expensive and strongest cranks available.  They are fully machined from a hammer forged bar (billet) of high-grade steel, heat treated and polished to further enhance its strength and fatigue resistance. These cranks have the ability to endure repeated high bending and twisting loads.  Attention to the these expensive details are very important to any high rpm race engines.  Like the 4AG crank, high rpm/endurance race cranks are generally fully counter balanced at each pin.  This shortens the torsional loads on the crankshaft by distributing the mass along the crank.  The one used in the 4A-G Formula Atlantic engine is TRD crankshaft, part number 13401-FT001.

 

For inspection purposes, the following tables have been included.  The first table lists the dimensions for the crankshaft main journal, the main bearing bore diameter and the crank pin diameter as they correspond to the factories inspection stampings on the crank.  The second table compares dimensional clearances between the different types of cranks and notes the approximate weight for each crank.  The third and forth tables lists the standard wall thickness of the OEM and TRD bearings.  And the last two tables reference TRD’s (large pin and small pin crankshafts) Group A and N2 main bearing bore, crank journal diameter and pin diameter requirements.

 

OEM Toyota	Stampings on Block or Crank	Dimension
Inside diameter of cylinder block main bearing bore	1 2 3	52.025~52.031mm (2.0482~2.0485inch) 52.031~52.037mm (2.0485~2.0487inch) 52.037~52.043mm (2.0487~2.0489inch)
Crankshaft journal diameter	0 1 2	47.994~48.000mm (1.8895~1.8898inch) 47.988~48.994mm (1.8893~1.8895inch) 47.982~48.988mm (1.8891~1.8893inch)
Crank Pin Diameter, Small, 4A-GEC, 4A-GECU, p/n 13401-16010	na	39.985 ~ 40.00mm (1.5742 ~ 1.5748inch)
Crank Pin Diameter, Large, 4A-GE, 4A-GZ, 20V,  p/n 13401-16020	na	41.985~42.000mm (1.6530~1.6535inch)

 

Even though the above table was referenced from Toyota’s own engine repair manuals, most high performance engine builders prefer not to assume or take a chance that the markings on anything would be correct.  They will (should) take the time to measure each and every component and figure out the required clearances.

 

Oil Clearance and Crank Comparison

Crank Type	Main Bearing Clearance	Thrust Bearing Clearance	Weight
TRD F/A p/n:13401-FT001-A	0.0020 ~ 0.0028inch	0.003 ~ 0.006 inch	Min. 28 lbs.
TRD AE86 & AE82  Group A, N2 p/n: 13401-AE801	0.050 ~ 0.065mm	NA
TRD AE92  Group A  p/n: 13401-AE902	0.055 ~ 0.070mm	NA
20V p/n: 13401-16020	Std. 0.015 ~ 0.045mm (0.0006 ~ 0.0018inch)	Std. 0.020 ~ 0.220mm (0.0008 ~ 0.0087inch)	12.695kg* (27.99Lbs.)
89 MR2, 91’ Hi Comp, 4A-GZ, etc. large crank pin p/n: 13401-16020	Std. 0.015 ~ 0.033mm (0.0006 ~ 0.0013inch.)	Std. 0.020 ~ 0.220mm (.0008 ~ .0087inch)
16V, early AE86 and AW11,  small crank pin, p/n 13401-16010	Std. 0.012 ~ 0.049mm (0.0005 ~ 0.0019inch)	Std. 0.020 ~ 0.220mm (0.0008 ~ 0.0087inch)	11.660kg* (25.70Lbs.)

*  Weight was measured on a single sample.

 

Please note the TRD Formula Atlantic (F/A) crankshaft is supported by a dry sump lubrication system, and it is not necessary to have “flats” machined into the nose of the crank to drive the “normal” oil pump mounted on the front of the engine.  The weight of a Formula Atlantic crank is governed by CART Toyota Atlantic rules. And each builder is allowed to “lighten” the crank by keeping the mass of the crank close to the mains.  This weight reduction is done to the counter balances and pins so long as the identifying marks are not removed and the weight is above the minimum allowable.

The crank pin diameter for Toyota’s Large journal crank should be within 41.985~42.000mm (1.6530~1.6535inch).  The crank pin diameter for the Small journal crank should be 39.985~40.000mm (1.5742~1.5748inch).

 

 

Toyota OEM Crankshaft bearings:

Part number (PNC 11711-):	Stampings mark #	Center thickness of bearing
Std. Size bearing 11701-15050-01  (-16010-01) 11701-15050-02  (-16010-02) 11701-15050-03  (-16010-03) 11701-15050-04  (-16010-04) 11701-15050-05  (-16010-05)	1 2 3 4 5	2.002~2.005mm (0.0788~0.0789inch) 2.005~2.008mm (0.0789~0.0791inch) 2.008~2.011mm (0.0791~0.0792inch) 2.011~2.014mm (0.0792~0.0793inch) 2.014~2.017mm (0.0793~0.0794inch)

 

TRD Group A, N2 Crankshaft bearings:

*  Bearing Set is 5qty.

 

Using a cylinder bore gauge, the oil clearance of the combined bearing thickness, crank journal diameter and the block’s main bearing bores should be 0.050 ~ 0.065mm(Small journal TRD Group A, N2), 0.055 ~ 0.070mm(Large journal TRD AE92 Group A),.

 

 

TRD’s  Crank Shaft Requirements *

 

*  Crankshaft bend <0.01mm

 

 

 

The above sketch of the 4A-G crankshaft shows the oil passage, where oil travels from the main bearing journal to the crank pin.  Please note that drilling the oil passage openings across the journal in this manner keeps the maximum amount of material (max strength) in the cross section that is subject to highest level of forces in shear. 

The above illustrations depicts the cross sectional, head on view, of various crankshafts.  There are several oiling strategies that have been used to move oil from the main journal to the rod journal.  ‘B’ – represents how the 7A crankshaft or the new 2ZZ transfers oil to the rod journal.  However there is only one opening in the rod journal and the main journal oil holes are off set from the center of the crankshaft.  This does not allow a constant 360 degree flow of oil.  ‘C’ – models the 4A-G crank.  Oil is available to the other side of the main journal and both sides of the rod journal.

16v AE86 Crank:

 

This photo is a small rod journal, 40mm, example.  Notice that it is fully counter balanced.

 

This photo of the small rod journal crankshaft shows the rolled fillets of the main bearing journal and the cross drilling of the oil passages.  Notice that the oil outlet / inlets are located in the center of the journal.

 

Notice the eight hole bolt pattern that is typical of all 4A-G cranks, and the pilot bearing pocket (a) for the T50 transmission.  Also notice the ‘ball bearing’ type plug (b) that closes off the end where the oil passage was created during the manufacturing process.

 

20v AE101 Carnk:

 

The above photo is a crank from an AE101 20valve engine.  It is identical to the other large, 42mm crank pin, 4A-G crank shafts.

 

 

This is a close up view of the large journal crank.  Notice the rolled fillets on the main journal and the number stamped on the counter weights.  Those numbers represent the bearing and journal size needed during assembly.  The earlier cranks where not marked on the crank but where marked on the block.

 

Stroker 16V small journal crank:

 

This photo is of a ‘stroked’ small journal 4A-G crank shaft.  Notice the welds on top of the rod journals and the resulting offset crank pin oil holes.  It is hoped that the quality put into this crank will be adequate for street use, as the quality of the welds can only be inspected by x-ray.

 

 

a - Close up view of the welding required to build up a “stroker” crankshaft rod journal.  b – Typical resulting void discovered during the re-grinding of the rod journal.  Wrong filler rod, i.e., less than idea material compatibility, voids, inclusions and thermal stress could lead to a weaken area if not done correctly.

 

 

 

 

 

 

7A Crank:

 

This is a photo of a 7A crankshaft.  Its stroke is 85.5 mm and weights 32.5 Lbs.  Though it is forged vanadium steel and fully counter balanced, there are features about this crank that one should be aware of that make it less than ideal for heavy duty competition.  Please note that this crankshaft can not fit into a 4A block.   The crankshaft pin diameter is 48.0mm.  The counter weight outside diameter is 69.0mm, and the counter weight “arm” thickness is16.75mm.  This makes the journal and counter weights too large and the resulting connecting rod angle too great for one to fit it in a 4A-G block.

 

 

 

 

This picture of the 7A crankshaft shows the location of the oil passages.  The holes/passages are all on the same plane.  This makes it easier for manufacturing since the crank does not have to be rotated or the drilling machines indexed 90 degrees.   Also notice this design does not require plugging.  However the placement of the oil holes and passages takes away needed material from a critical area and compromises the cranks ability to combat the larges forces being applied in shear on the journals and mains.

This photo shows the unique fillet rolling on both the crank main and rod journal fillets on the 7A crank.  This practice is to increase strength at the area that is subjected to the highest stresses.  Also notice the off center oil hole of the main bearing journal.  This position will not allow a full 360 degree supply of oil to the rod journal.  And it is positioned in a less than ideal area to take advantage of the maximum width and maximum strength of the journal.

 

This photo of the 7A crankshaft shows the less expensive manufacturing process of only drilling and tapping six holes for the flywheel.  Eight is the minimum needed for heavy duty usage.  However there is ample room to add a couple of shear pins.

 

This is a photo of an experimental light weight, 23.5lbs. Toysport 4A-G crankshaft.  Notice the larger counter weights have been ground away leaving these rather larger “shoulders” around the main bearing journals.

 

 

 

This is a close up view of the 5/16” - 18 socket set screw oil plug about to be put into the newly tapped oil passage way.  Again notice the large amount of material removed from the counter balance.  Use of this type of crank would require very light weight pistons and rods to help in balancing the complete assembly.

 

4A-G Front Pulley

One of the last items that is reviewed by the engine builder and often over looked as a performance item is the crank pulley.  All ‘stock’ OEM 4A-G front pulleys have a cast iron hub and the pulleys are machined for the reinforced, five rib, flat rubber drive belts.  It appears that early 4A-G engines (AE86) have isolated the inner pulley (pulley closest to the engine) by a thin layer of black rubber (elastomer) while the outer pulley is a contiguous part of the hub.  An exception to this is the 4A-GZ, supercharged pulley and the black top 20v pulley.  On these, both the inner and outer pulleys are isolated from the center hub. The layer of black rubber is relatively thin (aprox. 3 mm). 

 

Because Toyota balances their engines fairly well, this researcher would rather not categorize the 4A-G pulley as a harmonic balancer.   The typical harmonic balancer is constructed such that it has a mechanical means to dampen the rotating, torsional, imbalances caused from loose (poor) manufacturing practices and materials used for the crankshaft, pistons and flywheel.  Typical harmonic balancers are hollow inside, either filled with a heavy silicone like substance, used to counter imbalances, or have some other kind of heavy mass. The heavy mass is some times called an inertia ring.  This inertia ring is separated by a thin rubber buffer that isolates and absorbs the crankshaft’s natural frequencies and their harmonics.   It is a simple rule of physics that states that if the crank stays at its natural resonant frequency (at RPM), those vibrations (harmonics) will add to the destructive forces to eventually break the crankshaft.

 

The  4A-G pulley appears to be designed to absorb high frequency vibration caused from the optional power steering pump and/or air conditioner when they are turned on, or (though it’s hard to imagine) to isolate these accessories from the engine.  The GZ and late model 20v attempted to isolate the crank from all accessories.  In both models of pulleys, it is the inside and outside pulley that are isolated from the crank, and in all cases the mark for the ignition reference is not considered a “hard” reference since the rubber isolator could allow the outer rim of the pulley to move or slip from its position.

 

As a point of reference, the 4A-GZ supercharged inner pulley drives the water pump and super charger.  While the outer pulley drives the optional power steering pump, alternator and air conditioner.  With all other models, the inner pulley drives the water pump and alternator and the outer pulley drives the optional power steering pump and air conditioner.

 

As noted earlier, the 4A-GZ pulley not only isolates those accessories but also isolates the alternator and supercharger as well.   Because there is a layer of rubber between the inner pulley and the hub, one should verify the pulley is bonded to the hub and the rubber is not deteriorating.  It is also important to inspect the alignment between the pulley and the accessories. 

 

Among the various engine/chassis applications, there are noted differences between 4A-G pulley models.  The differences are the pulley diameters, position of the outside pulley (pulley furthest from the engine) and the location of the timing mark.  Therefore, one should always take note and verify the timing marks against top dead center of the number one piston. 

 

Even though it is common practice to pre-assemble an engine destine for performance duty, it is also necessary to verify the location of the timing mark and belt alignment prior to final assembly and engine installation into the vehicle.  It is becoming common to discover used 4A-G engines to not have their original pulleys.  Because of the uncertainty of using the correct pulley and the design (heavy and vague timing mark) of the OEM pulley, many engines destined for severe duty do not use stock pulleys.  TRD has listed a pulley with degree graduations marked on the edge, part number 13471-AE801.  Need less to say, the use of a purpose build performance oriented pulley usually means giving up the comfort of power steering and air conditioning.

 

For a more positive and efficient way to power accessories, TRD, like other racing engine builders has offered tooth pulleys to drive the external oil and water pumps, [Crank pulley part number 15152-FT001 (16 tooth), oil pump pulley part number 15102-FT001 (32 tooth) or for the N2; 15152-AE801 (17 tooth),  15163-KP611 (27 tooth) and water pump pulley 16371-AE801, alternator pulley 27411-AE801] [Crank pulley, water pump drive part number 16374-FT001 (20 tooth) and water pump pulley part number 16371-FT001 (30 tooth)]. 

 

The Formula Atlantic motor also has optional gear ratio pulleys available for the water and oil pump pulley cluster, e.g., part numbers 13521-FT002 and 13521-FT001.  The draw back of using a cogged belt is the noise and cost.  On the other hand, the draw back of using the stock, OEM, 5 rib drive belt is the unfortunate creation of friction and added side loads on the accessories’ bearings.  These belts require a specific amount of tension that ultimately results in friction, which is the performance tuner’s enemy.  One should consult the Toyota engine maintenance manual for the proper tension.

 

Toyota’s Recommended Belt Tension with tension gauge

	Water Pump	PS and/or AC	Alternator & AC	Alternator with out AC	With out PS
AE92 w/ 4A-G	115 lbs	90 lbs	------	------	------
AW11, MR2	115 lbs	105 lbs	------	------	-----
AW11 4A-GZ	115 lbs	------	85 lbs	115 lbs	-----
AE86, 4A-GE	115 lbs	115 lbs	------	------	130 lbs
AW11, 1989	115 lbs	115 lbs	------	------	------
AE111, “Black Top”	30 ~ 45 kg	-----	------	------	------
AE101, 4A-GZ	30 ~ 45 kg	-----	37 ~ 55 kg	30 ~ 45 kg	30 ~ 45 kg
AE101, “Silver Top”	25 ~ 40 kg	30 ~ 45 kg	------	------	------

PS = Power Steering, AC = Air conditioning.

Please note it is recommended to retention new belts after a minimum run time of 5 minutes.

Toyota recommends the use of Belt tension gauge: Nipondenso, BTG-20(95506-00020) or Borroughs, BT-33-73F

 

Choosing the right pulley ratio involves simple arithmetic.  One must take into account how fast the engine is to operate and compare that with the stock operation speeds.  The percentage difference is what is needed in terms of a new pulley combination.

 

An example of this would be to compare the crankshaft pulley of any later model 4A-G with the power steering pulley.  So when a crank pulley of 13.1cm diameter is turning at 7600 RPM, typical stock speed, the power steering pulley of 12.9cm diameter (ref. AE86, p/n 44311-12050) would be turning 7718 RPM.  This is expressed as the following ratio.

 

Therefore if the crankshaft is expected to see 9,000 RPM on a consistent basis, the crank pulley and/or the power steering pulley would have to change to keep the power steering pulley at the same RPMs as before.  The crank pulley would either have to be reduced in size (possibly using the early small diameter pulley, 11.7cm) or the power steering pulley would have to be increased in diameter.  As an example, by using a modified KAYABA 20V AE101 power steering pump / pulley, ref. p/n 44303-12010, of 14.36cm dia., this would give a crankshaft to power steering pulley ratio of 0.91:1, reducing the power steering RPM by 667RPMs (7,600 – 6,933).  Though this is not significant, it is something to consider when turning at 9,000RPM (power steering RPMs 8,190 vs. 9,140).

 

To help review the difference between the 4A-G pulleys, the following cross sectioned illustration defines the dimensions used in the accompanying table.

The above sketch shows a cross section of half of an early model pulley.   Dimension ‘A’ is the measurement from the bottom of the hub, where the pulley mates against the crank, to the ‘inner’ pulley’s first groove.  Dimension ‘B’ is the measurement from the same reference plane to the ‘outer’ pulley’s first groove.

 

Please note, if one is planning to use a stock pulley, the pulley may have to be rebalanced after the excess flashing is removed around the spokes of the pulley.  Therefore any work done to the front pulley should be done before the crank and other components are sent in for final balancing.

 

The following table compares the various 4A-G drive pulleys.  Please notice the different units of measure to avoid confusion.

 

 

Toyota Front Pulley (Part Code 13471)

Part Number	Application	Inner/Outer Pulley Diameter	A / B Location of first rib.	Weight	Comments*
13470-16010	AE86 8305~8708 AA63 8305~8507	13.1 / 11.7cm	0.65 / 1.67 inch	1542.4g	Casting mark “3”, timing mark notch on rim at 2 o’clock position closest to engine
13470-16030	AE82 8410~8808 AE92 8705~9205 AE101 9106~9505 (20valve)	13.1  / 13.1cm	0.60 / 1.45inch.	1564.9g	Inspection on AE101 pulley showed: Casting mark “11”, timing mark notch on rim closest to engine at 2 o’clock; rubber isolation marked 13470-16020
13470-16040	4AGZ AE101 9106~ AW11 8608~8912 AE92  8705~ 9106	14.6 / 13.1cm	0.61 / 1.44inch.	2461g	Casting mark “6”, timing mark notch on  inner rim at 12 o’clock position
13470-16020 13470-16020-30	AW11  8406~8912	13.1 / 11.6cm	0.6 / 1.45inch.	1403g	Casting mark “16”, timing notch on inner rim at 12 o’clock position; rubber isolation marked 13470-16020-30 (vehicle was not identified to verify vehicle part number combination) Outer pulley made for 4 rib belt.
Marking on rubber isolator 13470-16020-30 except for #4.  It was not visible	NA	13.1  / 13.1cm	0.6 / 1.45inch.	1546 ~ 1554g	Casting mark “14, 8, & 4”, timing notch on rim at 2 o’clock position closest to engine; rubber isolation marked 13470-16020-30 (vehicle was not identified to verify vehicle part number combination)
13470-16120	AE101  9605~ AE111  9704~ AE111  9505~	13.1 / 13.1cm	0.52 / 1.36inch.	1948g	Casting mark “J”, timing mark notch on rim at 2 o’clock position closest to engine; rubber isolation marked 13470-16120

*  Dimensions listed were from samples that had different cast numbers and other markings.  It is believed that the cast numbers would and could vary greatly and should not be used as a form of identification.  Moreover the small part numbers stamped on the rubber isolator ring may be difficult to see or have been obliterated through time.  All pulleys were for the five ribbed drive belt except as noted.

 

                                                     

The above photograph compares the early 4A-G pulley found on the AE86 (left) with that found on the AE111 (right).  Besides the different diameter of the front pulley, each pulley also differs in its location as it seats against the crankshaft timing pulley guide.   And not recognizing the differences could, at best, lead to premature belt wear or worst contributing to an accessory failure.

 

 

 

This photograph compares the large Cusco 4A-GZ (left) against a pulley found on an early AE92 (middle) and that of an AE86 (right).  It is interesting to note that Cusco modifies a Toyota 4A-GZ pulley.  The casting number and sometimes the part number are still visible.  Also notices that the Cusco front pulley has a thin rubber layer isolating it from the hub.  These other earlier models do not isolate the outer pulley.

 

 

 

         

 

Close inspection of the early AE86 4A-G pulley shows that only the inner pulley is isolated with a layer of rubber.  A closer inspection of this pulley also identifies it with its part number.  Also notice the hole on the back side of the pulley at the 11 o’clock position.  Toyota has balanced it.  The Toyota pulley is made of a brittle cast iron material.  It is strongly suggested that careful examination be done to inspect for damage on any pulley destine for reuse.

 

     

 

Unlike the AE86 and other early pulleys, this AE111 pulley appears to have been made by a different manufacturer, notice the ‘J’ as opposed to the three over lapping triangles.  Also notice that both inner and outer pulleys are now isolated with the thin layer of rubber.  At closer inspection, the front side shows the part number imprinted on the rubber, 13470-16120.  And at the 8 o’clock position on the inside side of the pulley are the holes used to balance the pulley.

    

 

Close inspection of this AE101 20 valve pulley shows that only the inner pulley is isolated with a layer of rubber.  Even though this example was taken from a ‘Silver Top’ 20 valve engine, closer inspection of this pulley identifies its part number as possibly being associated with an AW11.   Further examination of other ‘Silver’ top pulleys, e.g., marked #4 and #10, were either unreadable or were not identified.  However a ‘Silver’ top pulley marked #9 was also marked with part number 13470-16020.  Again notice the hole in the 11 o’clock position on the inside of this example.  This is a sign of balancing. 

 

        

 

These photos show a typical representation of an AE92 pulley.  Notice that only the backside of the pulley has a thin rubber layer isolating the pulley from the hub.  However, both the inner and outer pulleys have the same diameter.   Again all early pulleys appear to have been made by the same supplier which identified their pulleys with three over lapping triangles.  It has been observed that many of the AE92 “Hi-Comp” pulleys either had no part number identification molded into the rubber or were illegible, but several were identified with the same casting number as those found on the AE101 ‘Silver Top’ 20 valve engines, e.g., #12, #11, #9.

 

 

The above example is a pulley off a 4A-GZ.  Note the larger inner pulley used to drive the super charger and water pump, and note the outer pulley is also isolated from the hub by a thin layer of rubber that has the part number imprinted on it, 13470-16040.

The photograph above is TRD’s, p/n 13471-AE801, front engine pulley.  It is made from machined case iron, coated with a light varnish to protect it from corrosion.  Notice the pulley is cut for the unusual 3 rib belt (TRD p/n 00250-SP023 [3-5M-750]) to drive the water pump and alternator.  Please note TRD calls for a special water pump pulley,  p/n 16371-AE801, to drive it at reduced speed and to align it with the crank pulley.  The four holes on the front surface are to mount the 27 tooth pulley (TRD p/n 15163-KP611) to drive the dry sump oil pump.  It is interesting to note the holes used to remove the pulley from the crank shaft is the same distances apart as those on the stock ones, and thus able to use Toyota’s special crankshaft holding service tool, SST 09213-70010.  This particular example weighs in at 658.4g.  The diameter of the 3 rib pulley is approximately 90mm (3.541 inch).  There are no rubber insulation between the pulley and its hub.   From the back side looking inside the bore, you will notice a step.  Careful measurement shows that the outside surface should still seat against the crankshaft timing pulley guide.   The belt location height from the base of the pulley to the middle of the first groove (A) is approximately 0.71inch.  This is quite different from the other 4A-G pulleys.  Another unusual feature about this pulley is that it is marked in three areas.  At the 2 o’clock position, going clock wise, it is ma

    

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4A-G Flywheel

Though the fly wheel for the stock 4AG is quite adequate for the street and the intended purposes it was designed for, it is rather heavy for high performance applications.  More over because they are believed to be cast iron (designed for longevity and ease of manufacturing) it is not recommended they be lightened, but replaced with a steel alloy or an aluminum one expressly build by a reputable manufacturer, HKS, Toda, TRD, etc.   Though cast iron is thermally very stable, the cast iron manufacturing process typically results in uncontrolled pores and voids built into the product that result in its lack of strength, making them inherently weak.  An excessively lightened OEM flywheel could be dangerous.  On the other hand, a poorly manufactured or a bad designed flywheel can result in premature face wear, warped flywheels, excessive wear on the clutch, etc. 

 

The ideal weight is dependent on the intended application.  In a ‘drag race’ application the engine is always used in accelerating, a changing state from low RPMs to high RPMs and the goal is to put the power into the wheels and not into rotating the mass of the fly wheel.  On the other hand, a tractor pull competitor is looking for a constant torque and is not as interested in quickly changing the RPM of the motor.  Think of the fly wheel as a place to store energy that can be used to keep the engine idle going at very slow speeds, sustaining some power coming out of a turn or making the clutch slip a little while crawling in traffic.  Again it depends on the vehicle weight, intended application, the state of tune of the engine and clutch.

 

An example of a benefit from using a slightly heavier fly wheel would be in a high RPM, peaky engine, where one needs to smooth out the power pulses between cylinder firings at low speeds.  On the other hand, a modified street engine could benefit from a slightly lighter flywheel to help in quicker engine acceleration and decelerations.

 

The following table compares Toyota’s 4A-G flywheels to one another.  It is interesting to note that as time and performance moved on, so did the weight.  Toyota was lightening and increasing the friction surface area.

 

Toyota Fly Wheel Application Comparison

Part Number	Application	Weight*	Bell Housing code 31111,  Front cover code 31115C,  part number	Flywheel Comments
13405-19145	AE86 8305~8708 AE82 8609~8808 AE92 8705~8905 AW11 8406~8506	15.85Lbs.	31111-12050   31115-12021, -12040, -16040 31115-12020	Weight was from a slightly lighten ed example. Clutched face design: stepped  0.020 inch.;  Friction area:  200mm outer dia. x 140mm inner dia.
13405-16030	AW11 8506~8912 AE92 8905~9205 AE101 9106~9603	15.45Lbs.	31115-12021, -12022, -12040 31115-12040, -16040 31115-12040, -16040, -16041	Clutched face design: stepped  0.020 inch.;  Friction area:  212mm outer dia. x 140mm inner dia.
13405-16050	4AGZE AW11 8608~8912 AE92  8705~ 9010		31115-17011, -17013 31115-17012, -17013, -12070	Friction area:  224mm outer dia. x 150mm inner dia.
13405-16051	4AGZE AE101 9106~9505 AE92  9010~9106	12.70Lbs.	31115-12070, 12071 31115-17013, -12070, -12071	Clutched face design: Cupped   inch.;  Friction area:  230mm outer dia. x 150mm inner dia.
13405-16110	AE101 9505~0206 AE111 9505~0207	13.30Lbs.	31115-16042(6sp) 31115-16040, -16041, -16042	Clutched face design: stepped  .020 inch.;  Friction area:  212mm outer dia. x 140mm inner dia.

* Weight of fly wheel did not include clutch/pressure plate assembly, or fasteners.  Listed are standard friction surface area dimensions.  Actual dimensions varied by several millimeters.

All Toyota 4AG fly wheels have an 8 hole bolt pattern for the 4A-G crank.

When attaching the fly wheel to the crank, consult the Toyota Repair manual for the torque and patter sequence. 

All Toyota 4AG fly wheels have the same 106 tooth, 27.2cm diameter ring gear, Toyota part number 13453-10010.  (It is the same one used on the 4AFE, 5AFE, 7AFE and 2ZZGE engines)

 

 

With any review of the Toyota 4A-G flywheel, one is surprised to find the numerous combinations of clutch covers (pressure plates) and clutches that were available to the various flywheels.  The following tables attempts to list them against the different flywheels.  However, no attempt has been made to evaluate them or comment on them for performance duty.

 

Toyota’s Fly Wheel , Clutch Cover, Clutch part number groupings

	Fly Wheel  Part Number 13405 -	Application	Clutch Cover Assy. (Pressure Plate assy.)  Part Number  31210 -	Clutch Disk Assy. Part Number  31250 -	Comments
	-19145	AE86 8305~8708 AE82 8609~8808 GTS AE92 8705~8905 AW11 8406~8506	-12080 (-12120) -12080 (-12120, -12121) -12120 (-12121) -12080 (-12120)	-12182 (-12183, -12184, -12290) -17010 (-12290) -17010 (-12290) -17010 (-12290)	Clutch size: 200 x 140 x 3.5mm Spline size: 21 tooth x 15/16 Inch dia. clutch is semi- resin molded;  Spr. force: 360~430Kg
	-16030	AW11 8506~8705 AW11 8705~8912 AE92  8905~9205 AE101  9106~9505	-17010 (-12201) -17011 (-17012, -12150, -12151, -12152) -12150 (-12151, -12152) -12200 (-12201) -12220 (-12221), -12150 (-12151, -12152)	-17020 -17020 (-12320) -17020 (-12320, -12360) -12320 (-12360)	Clutch size: 212 x 140mm; Spline size: 21 tooth x 15/16Inch dia.; Spr. force: 350~450Kg
	-16050	4AGZE AW11 8608~8912 AE92  8705~ 9010	-17020 (-17021) -17020 (-17021)	-17030 (17031) -17030 (17031)	Clutch size: 224 x 150mm; Spline size: 21 tooth x 11/8 Inch dia.; Spr. force: 400~530Kg
	-16051	4AGZE AE101 9106~ AE92  9010~9106	-12170 -12170	-12230 -12230	Clutch size: 230 x 150mm; Spline size: 21 tooth x 11/8 Inch dia.;  Spr. force: 550Kg
	-16110	AE101  9605~ AE111  9704~ AE111  9505~9704	-12152 -12201 (-12152)	-12360 --12380 (-12370, -20280)	Clutch size: 212mm; Spline size: 2 1 tooth x 15/16 Inch dia.; 6sp

Note: Spline size denotes number of teeth x diameter in inches

 

TRD’s Clutch Cover, Clutch Disc part numbers

 

 

TRD’s  4AG  Clutch Cover spec.

Part Number	Face dimensions( mm)	Spring Force
31210-AE100	f 212  x  f 140	700Kg
31210-AE051	f 230  x  f 150	800Kg
31210-AE852	f 200  x  f 140	550Kg
31210-AE851	f 200  x  f 140	600Kg
31210-AW151	f 212  x  f 140	NA
31210-AW161	f 224  x  f 150	700Kg
31000-AE801	f 184  x  f 134	650Kg

Typical Stock spring force = 430Kg.

 

TRD’s  4AG  Clutch Disc. – Dry single plate diaphragm

Part Number	Face dimensions( mm)	Notes
31250-AE851	f 200  x  f 140 x 3.5	Ferodo, 4A-G Non super chg’d
31250-AE852	f 200  x  f 140	Ferodo, 4A-G Non super chg’d
31250-TA461	f 200  x  f 140 x 3.0	Metallic, 4A-G Non super chg’d
31250-AW151	f 212  x  f 140	Ferodo, 4A-G Super chg’d
31250-GA661	f 224  x  f 150	Metallic, 4A-G Super chg’d
31000-AE801	f 184  x  f 134 x 0.5	Metallic, B&B type

Note: Ferodo are resin  molded.

 

When comparing and considering a high performance flywheel replacement for the 4A-G, more than weight should be evaluated.  Having two flywheels with the same weight could have very different moments of inertia.  If one imagines a flywheel build like a donut, with most of its mass located near the ring gear and another one with most of its mass located near the axis of rotation it is easy to see that the donut example would have a greater moment of inertia and thus slower to respond to accelerations or decelerations.

 

Flywheel Comparison

Mfg., & Part number	Weight	Notes
TRD,  13451-AE851	9 Lbs.	Takes std. size clutch, accepts metallic, Ferodo and stock discs.
TRD, 13451-AE801		Borg & Beck type (single plate with an adapter ring) – exclusive designed for 13100-AE801 clutch.
TRD,  13451-AE862, Non super chg’d.	13.4 Lbs.	Takes std. size clutch, accepts metallic, Ferodo and stock discs.
TRD,  13405-4AG01	10 Lb. 14oz
TRD,  13405-AE871	6.7Kg
TRD, 7020XX-10023J	11.5 Lbs.	High-tensile-strength ductile iron, for Corolla, ‘85~7; MR2, ‘85~89; F16 ’87.
TODA,  4AG ~ 4/1987	3.7 Kg.	AE86 & AW11, heat treated, harden & heat treated Chromium molybdenum, Ultra-Light Weight, 200mm friction face
TODA,  4AG ~ 4/1989	3.7 Kg.	AE92, heat treated, harden & heat treated Chrome moly
TODA,  4AG ~ 4/1989 ~ up	4.4 Kg.	AE92, heat treated, harden & heat treated Chrome moly
TODA,  4AG	4.4 Kg.	AE101, heat treated, harden & heat treated Chrome moly
TOM’s,  13405-TAE10	3.5 Kg.	AE92, AE101, uses clutch disk 31250-AE852 & clutch cover 31210-AE852
HKS,  2608-RT003	12 Lbs.	Black nitride finish
C-ONE, FF1340-AE100	4.4Kg	Chrome-molybdenum
C-ONE, FF1340-AE800	4.0Kg	Chrome-molybdenum
JUN,  2001M-T005	4.1 Kg.	AE86, Forged Chrome-molybdenum steel
JUN,  2010M-T005	3.6 Kg.	AE86, Lightened Forged Chrome-molybdenum steel
JUN,  2001M-T006	4.6 Kg.	AE101, Forged Chrome-molybdenum steel
JUN,  2001M-T007	4.7 Kg.	4AGZ, AW11, Forged Chrome-molybdenum steel
JUN,  2001M-T020	4.8 Kg.	4AGZ AE101, Forged Chrome-molybdenum steel

 

Please note that many replacement flywheels have the ring gear machined into the flywheel.  This is possible with a steel alloy such as Chromium-Molybdenum (typical composition: 0.35% Carbon, 0.30% Manganese, 1% Silicon, 5% Chromium, 0.4 ~ 0.9% Vanadium & 1.5% Molybdenum).  Chrome Moly is a good material choice when you have to compromise design issues like wear, toughness and warping. 

 

On the other hand, custom made aluminum flywheels require the use of Toyota’s ring gear and a special steel friction insert.  This hardened surface is often called a heat shield.  The heat shield can be plasma sprayed (then ground smooth) and then screwed or riveted onto the flywheel.  Since the flywheel also acts as a heat sink to dissipate energy (heat generated by slippage) from the clutch assembly, an aluminum flywheel design could be an advantage.

 

Never the less, clutches and flywheels do wear. To recondition the flywheel face, it is best done by grinding.  A special machine is used in most shops.  Please note that the small step between the friction face and where the cover mounts must be maintained and it is usual to finish the outer periphery of the flywheel with a lathe.  The exception in maintaining this step is the GZ flywheel where the flywheel has special ‘stand offs’ machined into the flywheel (also known as a cup design).  Again, that “step distance” should be maintained to preserve the clutch disk to friction face clearances and spring force of the clutch cover.

 

Normally the step should be about 0.020inch. ±0.002 inch.  This will ensure the correct height for the clutch cover to maintain the proper clamp load.  It is important to maintain the parallel relationship between the flange face (where it bolts to the crankshaft) and the friction face and the overall trueness of the friction face itself. 

 

Even though the earlier repair manuals specify the maximum run-out of the flywheel friction face as 0.2mm (0.008inch.), the later models specify it to be 0.1mm (0.004inch.). 

 

After machining and ring gear inspection (replace if necessary) the flywheel should be checked for balance, and corrected if required. 

 

 

 

Though this is not made for the 4A-G, it is an example of an aluminum flywheel.  This one is from Toysport.   Notice the friction plate and the hardware that holds it in place.  The ring gear is also a separate piece.  And because the flywheel is made of aluminum, a slight interference fit has been designed into its assembly.  Heating the flywheel up so that it can expand and be able to be assembled on to the crankshaft is typical.  Aluminum expands at twice the rate of steel.  It is good assembly practice to pre-assemble the flywheel, bell housing and even the transmission together to rotate and check excessive flywheel run-out or other interferences.  Even though many aluminum flywheels are CNC machined it is always recommended to check the balance with the clutch, pressure plate and the engine together.  During periodic maintenance, one should check for possible fatigue cracks and loose hardware.  The areas to inspect are the crankshaft register, flywheel to crank mounting holes and the ring gear.  Extreme heat can also affect the dowel pin areas and or cause the ring gear to grow and not return to its static diameter.

 

As with all new flywheels the friction surface should be thoroughly cleaned and any protective oil film removed.  It is recommended that new replacement friction surfaces be installed by the manufacturer, when needed.  However since these steel heat shields are typically heat treated all the way through, they can be reground assembled.

 

 

This is an example of the early model, AE86, flywheel.  They are rather heavy and the friction area relatively small, but the alignment pins and holes are inside the ring gear diameter.

 

 

 

 

 

This photo is of an AE101 flywheel.  Notice to keep the same size ring gear, a larger diameter flange was needed to accommodate the larger clutch cover.  Also notice the undercut in the flywheel next to the mounting holes.  It appears that Toyota made an attempt to lighten this design ever so slightly.

 

 

 

 

 

This is an example of Toyota’s AE111 4A-G 20 valve flywheel.  Notice the minimum amount of material next to the ring gear.  Also notice the areas where the clutch plate would normally mount, have been turned to into “ears”, or little ledges.  This is all in the effort to reduce the rotating mass and interia.  The friction surface has also been slightly enlarged.  Also notice the bright shining spots on the friction surface.  These were caused by the clutch slipping.  This flywheel should be reground before being installed.

 

 

This is an example of a HKS steel flywheel.  Ironically the weight of this flywheel is very close to the AE111.  Although the design and production of the HKS Steel flywheel pre-dates the AE111 by several years, it is curious that they are so similar.  Notice the Nitride (blue) finish to protect it from corrosion.  And note that the ring gear is machined into the flywheel.  It can not be replaced,

 

 

 

 

 

 

This photo is an example of the 4A-GZ flywheel.  The friction surface area is the largest of the 4A-G flywheels.  Notice that the pressure plate would be mounted to the raised stand offs.  This would allow the use of a much thicker clutch disk and heavier pressure plate springs.

 

 

 

 

 

 

 

 

These photos are an example of TODA’s ultra light flywheel for the AE86.  Notice the smaller 200mm friction surface.  And notice the extra effort to lighten the outside of the flywheel, holes and the thin material supporting the ring gear.  This effort reduces the moment of inertia, allowing less energy needed to speed up the flywheel as compared to an identical weight flywheel with more of its mass located towards the ring gear.  Also notice the ring gear machined into the flywheel.  Once the ring gear is damaged the flywheel will have to be replaced.