Finding true TDC on a 7AG

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oldeskewltoy
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Finding true TDC on a 7AG

Postby oldeskewltoy » Fri Mar 29, 2013 1:37 pm

THIS maybe why your 7AGE is slow... and sluggish :shock:

I FINALLY got my hands on an assembled 7AGE and the owner allowed me to check TDC by using a piston stop.

You CAN'T do cam timing... if you don't KNOW where TDC is......... well... here it is :ugeek:

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Above is TRUE TDC... as measured by using a piston stop. 2 teeth off AT the CRANK! Note the alignment bump is 2 teeth off from the crank pulley groove

I always figured that Toyota changed the position of the TDC dot on the 7A oil pumps and crank timing pulley. I figured (correctly... in many cases) that people had no idea where true TDC was because they were using a 4AG timing pulley, and using a 7A reference........

:D
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Re: Finding true TDC on a 7AG

Postby gaijin_rokurunner » Fri Mar 29, 2013 7:21 pm

Thats why Nagisa auto sells their kits with properly sized cam pulleys to compensate for the timing difference because of the taller block... Good stuff Dan have that stickied and put in the tech area...
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Re: Finding true TDC on a 7AG

Postby yoshimitsuspeed » Sat Mar 30, 2013 9:37 am

What OST is talking about doesn't even get around to the changes due to the block height. He is just saying that if you mix and match 7A and 4A timing pulley and oil pump the references will be wrong due to having different locations.

How many people do this though? Do you have to mix and match those parts? Or is it just possible that some may?

I would think a motor would barely run if even at all at two teeth off on the crank.

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Re: Finding true TDC on a 7AG

Postby mikeyee » Sat Mar 30, 2013 2:22 pm

this is good to know! thank you!

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Re: Finding true TDC on a 7AG

Postby jdm86gtz » Sat Mar 30, 2013 2:44 pm

The oil pump timing dot looks to be down where a blacktop oil pump has it's dot in that picture. Maybe, might be worth a look into, but you'll need a BT crank pulley to match as the timing pulley is wider than other 4AGs.
I'm hoping to pic up a 7AF during the week and have a BT timing pulley to compare.

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Re: Finding true TDC on a 7AG

Postby carbd7age » Sat Mar 30, 2013 4:34 pm

Wait wait wait wait wait. I lined up the 4AGE pulley notch to the 7AFE oil pump bump, and I eventually got it running. I corrected cam timing with adjustable cam gears, but the overall timing is a smidge off??? So this could be why it's so dang hard to start? PS it felt plenty beefy when it ran for the short while I got to drive it.

Now when I built my engine, I checked the gear-to-pump timing mark without the cylinder head and I swear it was TDC with the notch and bump lined up. I didn't have a fancy gauge or anything, I did it by feel. Could it be off that much?
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Re: Finding true TDC on a 7AG

Postby oldeskewltoy » Sat Mar 30, 2013 5:25 pm

A piston stop is under $15.00 from Summit, Amazon, or Jegs...

Image

with that tool it is possible to KNOW exactly where top dead center is
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Re: Finding true TDC on a 7AG

Postby carbd7age » Sat Mar 30, 2013 6:46 pm

So that dealy screws in the spark plug hole, and you slowly tighten the center bolt until the piston touches it at the top of the stroke? Freakin easy. I reckon I need one.
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Re: Finding true TDC on a 7AG

Postby Deuce Cam » Sat Mar 30, 2013 9:18 pm

There's a little more to it than that, but not much. The video below gives a good description of the whole process. The author describes how to go about adjusting the length in the comments - he forgot to mention it in the video.

http://www.youtube.com/watch?v=PD0ZRc7Dy28

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Re: Finding true TDC on a 7AG

Postby LongGrain » Sat Mar 30, 2013 11:26 pm

what ever happened to sticking a long screw driver in the spark plug hole and rotating the crank until the screw driver is at its highest point?

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Re: Finding true TDC on a 7AG

Postby Deuce Cam » Sun Mar 31, 2013 1:01 am

You can do that, but it's not as precise.

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Re: Finding true TDC on a 7AG

Postby carbd7age » Sun Mar 31, 2013 4:18 am

I guess just like using my hand with no cylinder head, there is a range of motion to where the piston feels like it doesn't move and stays at the top. I thought I halved that range for true TDC, but a stop thing would be more accurate.
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Re: Finding true TDC on a 7AG

Postby tiprock » Sun Mar 31, 2013 9:29 am

besides a piston stop, i think u also need a degree wheel.
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Re: Finding true TDC on a 7AG

Postby gaijin_rokurunner » Sun Mar 31, 2013 9:37 am

There is actualy a shop in New Zealand or Australia that made a lower gear that corrects the timing issue when using the g head...i will post the link when i find it
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Re: Finding true TDC on a 7AG

Postby carbd7age » Sun Mar 31, 2013 11:46 am

gaijin_rokurunner wrote:There is actualy a shop in New Zealand or Australia that made a lower gear that corrects the timing issue when using the g head...i will post the link when i find it

I heard about that when I built my engine, but I already had a set of adjustable cam gears. I'll try the piston stop deal and see if that helps my starting problems.
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Re: Finding true TDC on a 7AG

Postby kaosboss » Sun Mar 31, 2013 4:38 pm

.
Last edited by kaosboss on Sun Mar 31, 2013 5:35 pm, edited 1 time in total.

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Re: Finding true TDC on a 7AG

Postby gaijin_rokurunner » Sun Mar 31, 2013 4:52 pm

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Re: Finding true TDC on a 7AG

Postby kaosboss » Sun Mar 31, 2013 5:34 pm

Image

Got that from barry in new zealand

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Re: Finding true TDC on a 7AG

Postby BoRoYaSui » Mon Apr 01, 2013 10:31 pm

can someone with a 7age measure with a degree wheel how much the timing mark is off using a 4ag gear?

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Re: Finding true TDC on a 7AG

Postby oldeskewltoy » Tue Apr 02, 2013 8:33 am

gaijin_rokurunner wrote:There is actualy a shop in New Zealand or Australia that made a lower gear that corrects the timing issue when using the g head...i will post the link when i find it


not picking on you Tony... but really... with all you have into your build.........


from another forum wrote:or you could get a crank sprocket from bazda that has been modified to allow for the change in TDC position ;)

You MIGHT do that........ but you still would NOT KNOW where TDC was....

TDC means TOP, DEAD center..... not... oh..pretty close to it

IF you are setting cam timing... you need to KNOW EXACTLY where TDC is... and NOT a dot and a notch
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Re: Finding true TDC on a 7AG

Postby carbd7age » Tue Apr 02, 2013 5:20 pm

Yeah.....you right. :oops:
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Re: Finding true TDC on a 7AG

Postby gaijin_rokurunner » Wed Apr 03, 2013 8:18 am

Lol @ Dan...well i dont have a 7ag so i never used the item thats why i didnt know the link off the top of my head...plus alot of my stuff is custom so I dont have much purchased from others on my setup...you should know all this info anything....your the toyota encyclopedia i should say really to u for not knowing about that sprocket ! Haha
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Re: Finding true TDC on a 7AG

Postby greenae102 » Thu Apr 04, 2013 1:44 pm

on my 7ag 20v i used the 7a gear, lined it up with the 7a oil pump mark and lined cam gears up according to the 4ag bt manual floating around all over the net. it started just fine over a year ago and still runs strong with same timing settings. its not bad on power either bc i can easily pull away on my buddy's stock 20v :roll: no adustible gears on mine either. i dont see how so many have timing issues...
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Re: Finding true TDC on a 7AG

Postby carbd7age » Thu May 09, 2013 4:50 am

Back from the dead. I have an idea. I have the original 7afe lower timing cover and crank pulley. Could I just use those to find TDC? I want to use a piston stop as well, just to make sure.
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Re: Finding true TDC on a 7AG

Postby oldeskewltoy » Thu May 09, 2013 8:56 am

TDC is a single point on a 360 degree* circumference. The dimple and the groove are semi vague at best and could easily be off by 2 or maybe as much as 3 degrees and you wouldn't know it.


* - remember each degree is broken up by 60 minutes, and each minute of a degree is broken down to 60 seconds. A single point is rather small :shock:
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Re: Finding true TDC on a 7AG

Postby yellowsnow4free » Wed Jun 26, 2013 10:19 pm

This is an interesting thread :)

Since I haven't quite wrapped my brain around all this yet, would potential 7AC builders have to deal with this too? I assume for a 7AC build you'd use the 4AC lower timing cover, crank pulley, and crank sprocket, but IDK for sure.

But when in doubt, it makes sense to me to use the piston stop :)

carbd7age wrote:Back from the dead. I have an idea. I have the original 7afe lower timing cover and crank pulley. Could I just use those to find TDC? I want to use a piston stop as well, just to make sure.

Any updates on this Eric? Just curious :)

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Re: Finding true TDC on a 7AG

Postby carbd7age » Thu Jun 27, 2013 4:03 am

I guess a small update: I actually FOUND the front cover and crank pulley off my donor engine lol.
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Re: Finding true TDC on a 7AG

Postby Garage7RP » Thu Jun 27, 2013 3:51 pm

carbd7age wrote:I guess a small update: I actually FOUND the front cover and crank pulley off my donor engine lol.


Here is another way of finding TDC on a 7AG without a piston stop.
Using the 7A oil pump and oil pump cover with the 7A crank gear, line up the timing marks from the crank gear versus the oil pump cover. Ensuring that nothing will move, remove the 7A crank gear and install the 4A crank gear then create the new marking on the gear by matching the dimple on the 7A oil pump cover. At this point, you may leave it as is if you would like to use the 7A oil pump (high volume) vs. 4A oil pump (high pressure).

If you are decide to use the 4A oil pump, from the previous step and ensuring nothing will move, remove the 4A crank gear, 7A oil pump and oil pump cover. Install the 4A oil pump and oil pump cover, and 4A crank gear. With the 4A crank gear in place and noting the new timing mark you created on the gear, create a new dimple on the 4A oil pump cover matching new timing mark on the oil pump gear.

I hope this helps and made sense :lol:

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Re: Finding true TDC on a 7AG

Postby yellowsnow4free » Thu Jun 27, 2013 11:53 pm

Garage7RP wrote:Here is another way of finding TDC on a 7AG without a piston stop.
Using the 7A oil pump and oil pump cover with the 7A crank gear, line up the timing marks from the crank gear versus the oil pump cover. Ensuring that nothing will move, remove the 7A crank gear and install the 4A crank gear then create the new marking on the gear by matching the dimple on the 7A oil pump cover. At this point, you may leave it as is if you would like to use the 7A oil pump (high volume) vs. 4A oil pump (high pressure).

If you are decide to use the 4A oil pump, from the previous step and ensuring nothing will move, remove the 4A crank gear, 7A oil pump and oil pump cover. Install the 4A oil pump and oil pump cover, and 4A crank gear. With the 4A crank gear in place and noting the new timing mark you created on the gear, create a new dimple on the 4A oil pump cover matching new timing mark on the oil pump gear.

I hope this helps and made sense :lol:

Lol, I think it makes sense, although something more visual (pictures or a video) would make it easier :P

Thanks for the info though; I was trying to wrap my brain around this and haven't seen anyone else online mention this method :)