I recently broke in my freshly rebuilt 4age 16v after it spun rod bearing last summer. As of now, it has about 250 miles on it and I noticed this noise (Lower gronny noise after blipping the throttle). https://www.youtube.com/watch?v=jspZVGnszIU It was a lot more faint at first start (kinda sounded like a small diesel engine) and now has grown into more of a knock over the past few days. I just pulled the engine to check the rod and main bearings but nothing looked abnormal. Plastic gauged the rod journals and all were within spec, all rod journal diameters were within .01mm of each other, no spun bearings or anything. I already checked the valve adjustment by using a feeler gauge under the cam lobes according to repair manual and all were within the specified tolerances. The only thing I can think of now is either piston slap or something as far as a bad wrist pin. One reason that led me to believe this could be the cause is that I used 1 single different rod/piston out of a donor engine to replace the rod that had the spun bearing in it. Too much material was taken out of the old rod so out of the 4 rods and pistons of the donor engine I chose the one that was closest to spec and didn't reuse the old piston that was originally in my motor as I don't have a press to press the wrist pin out to swap the old piston onto the "new" rod. If it helps any the donor engine was a turbo 4age bigport that someone ran boosted on stock internals and threw a rod so it's not a aftermarket rod and piston or anything. I also tried using a TRD metal head gasket on the rebuild which only lasted 100 miles before it started leaking into the 4th cylinder. I don't know that I caught it in time from it possibly overheating by the time I made it home but I don't know if that would have anything to do with the noise, just throwing out any information I have that may have something to do with it.

Specs of my engine after rebuild:

Toyota 20v Silvertop oil pump
Stock crank turned down .25mm
Sealed power rod bearings .25mm undersized
Sealed power main bearings .25mm undersized
Sealed power premium piston rings
Toyota water pump
Cylinder head resurfaced, ported, & polished
Toyota OEM Headgasket
ARP Head studs
All new Toyota seals and gaskets
All oil supply and drain galley turns and bends smoothed

Just wondering if anyone would be able to give some insight of what they might think it is. I tried doing a little searching but didn't come up with much or even a video of a 4age sounding close to mine. Any help would be appreciated,
Thanks Guys.

Did you measure the bores for round and measure the piston clearance?

I have not pulled the head off yet but that was gonna be the next step. I checked it all before original rebuild and all was within oem standard limits

Timing checks out?

EGR system good?

Pidge526 wrote:It was a lot more faint at first start (kinda sounded like a small diesel engine)
and now has grown into more of a knock over the past few days.

I'd suggest that you check the condition of your timing belt tensioner.
One time I had a tensioner go bad and to begin with it was just a tiny knock
that I would only hear coming to a halt at the lights with the window down.
But after a while it got louder until you could hear it when coming to a stop
and when taking off. With the hood up and the engine idling (revving it gently
like you were doing) it sounded exactly like a bearing knock... even had my
mechanic fooled. But when we tracked it down, sure enough, the tensioner
bearing was on the way out. New tensioner and problem solved.

Worth a look if you haven't already changed yours.

Cheers... jondee86

Timing was good (both mechanical and ignition dead on) and the tensioner was replaced during the rebuild. Turns out piston #3 has a bit more clearance than it should which I think was causing the slap. It was also the piston/rod I pulled out of the other engine so go figure. I guess right now I have the original piston from the bad rod that I'm going to try to swap onto the good rod as it is a tighter clearance than the one that is on there now.

While you have got it in pieces it would be worth checking the small end bearings.