Need help to determine pistons that are installed

[Turbo Guru]

As some of you already know I have my head off and may do a rebuild. My question is about the pistons that are in my motor. I can only see the tops of the pistons and I am curious as to which they are. The reasons I am curious are:
1) The car already has ALL of the free mods done.
2) The car already has some upgrades done ie- ACT clutch, UICP, K&N, Short- throw shifter, aftermarket (dejon?) throttle body elbow.
3) The transmission has been rebuilt.
4) The motor has been apart (the person said it was rebuilt) and the timing belt, etc... has been changed.
5) The question at hand is maybe this guy already had 2G pistons or some others installed. I would call him and ask, but he is out of town for a month or so and I don't have that long...

The pistons have no writing or marks, flat tops (with no dish) and, have standard valve reliefs. The compression test I ran to find the head gasket leak showed 180, 176, 180, 120. The compression is pretty high for 7.8:1 1G pistons with no buildup on the piston or in the combustion chamber. I was under the impression that the compression results for a 1G should be in the 150's.

Does anyone have compairson (sp?) pictures of the tops of the 1G and and 2G pistons? I will try to take some pics of what I see and post them tommorow.

 

[larryd]

nada clue but you can see pictures of some pistons from website to website.. like www.turbotrix.com www.machv.com www.extrememotorsports.com etc etc.. they all have pics of pistons if I recall..

 

[NDgsx]

Can you get a picture? If they really are flat tops they are DEFINETLY aftermarket and pretty forkin high compression. I think the 10:1 pistons Marco at magnus runs are flat top. 9:1 JEs and Ross's I have looked at are dished.

 

[Turbo Guru]

Actually, I was mistaken (I'm never wrong, ) after being over-sprayed with copper seal I discovered that they have a slight dish and "< 63D" on the face. With the carbon on the piston face it was not visible (no shadows). So what pistons are these? Remember the compression test read 180psi which is high.

 

[dsmtrance]

Funny, same here. I pulled the head of my Talon to find out that "some" of the mods I was told the car had it didn't!!! I was pissed. Anyways, I also am wondering what pistons I have. My car pulls 190-194psi SOLID across the board. I haven't cleaned off the tops of them yet to see if there is any writing...I'll do that! They're definitely not stock 91's though Oh well, we'll see.

 

[Turbo Guru]

Mine might be that high also, I test the compression with the car cold considering that I couldn't run it to warm up because of the blown head gasket. So my compression test #'s were 180,176,180,120 cold! (gasket was blown on the 120 cylinder) Someone please tell me what these are I have a hard time believing they are stock 1G pistons.

 

[Turbo Guru]

ttt

 

[dsmtrance]

Mine might be that high also, I test the compression with the car cold considering that I couldn't run it to warm up because of the blown head gasket.

I'm not too sure about the whole hot/cold compression test thing (even though I know it says to do it on a warmed up motor). My compression results were ALWAYS 190-194psi SOLID across...hot OR cold. And when I pulled the head off I did NOT see very much carbon build-up at all (enough for me not to be able to "see" if there was anything written on the piston though...kinda splotchy). Plus it's obvious that the motor has been redone. There is no balance shaft either. I'm just wondering if they are actually the JE 9.0:1's that he SAID were in there!!! He said the head had tit. retainers and stock size SS valves too. It had neither! Now it's getting the Crower spring/tit. retainer kit put in as we speak to go with the new Web cams. Plus I NEVER had any real issues with the motor. Other than pushing coolant under boost you'd never have known the car had a bad HG. Compression was 190-194 the WHOLE time...never flinched! I just decided to go ahead and change it finally, that's all. Well, I'm gonna try to clan up the tops of the pistons this week and see what, if anything...I hope not!, is on them. We'll see.....

 

[Turbo Guru]

ttt

 

[All4Smoking]

all factory pistons have a 4 digit number on the top. I think there is actuall a letter instead of a number, but there are four. anyway, i would measure the piton to cylinder wall clearence, that would tell you most likely if they are aftermmarket because je's are forged so the clearance is going to be a lot bigger than factory cast pistons. check it out.

 

[Turbo Guru]

These had only three numbers/ letters "63D" on the "bottom" face of the piston. The arrow is separate from this designation toward the top of the piston face. I don't know the piston clearance because they are still in the block which is still in the car. BTW, I get my head studs tommorrow and will be praying the rings are good. All for now... Joe

 

[All4Smoking]

$100 says they are factory. sorry

 

[NDgsx]

So there is a arrow pointing to the timing belt side of the engine? Then they are definetly stock pistons.
Aftermarket pistons do not have offset wrist pins so they have no arrow.

 

[Turbo Guru]

I figured they are stock but are they 1G or 2G?

 

[dsmtrance]

Well, maybe I got lucky on this one!! I looked at the pistons again, and while there are still some "chunks" of carbon on the tops of them you can still see pretty much all the tops. I do not see ANY #'s or letters on them. They look a LOT like these (JE's)...just not shiny (same "dish"). Anyways, at least maybe the bottom end is as stout as he said it was!!!

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[Turbo Guru]

congratulations, I hope you are right. It sucks to be screwed. Good luck.

 

[Turbo Guru]

I did a compression test after installing the head gasket, some of them were as high as 195! I believe the pistons are stock but they must be 2G to have compression #'s that high. All for now, tommorrow I have to take it apart AGAIN, don't ask I am too mentally and physically tired to go into it right now. I'll let you guys in on my problems later. Peace... Joe

 

[Turbo Guru]

Eureka!!! I think I just figured out the answer to my piston question. I happened to surf onto http://www.turbo4wd.com/ and was looking at his pages concerning the 1G head swap onto his 2G an found this picture (see image.) The pistons in the picture have the upside down "63D" and look just like mine. His car is a 2G 7bolt block, mine is a 1G 6bolt block. I believe that these pistons are the same as mine, which would make them 2G 8.5:1 compression pistons! Although the question still remains; do 1G pistons have the same "63D" on their face? Any help is greatly appreciated. Thanks in advance... Joe

 

[NDgsx]

The pistons out of my old 91 (was completely stock) have the same letters. Their dish is about .12". You could measure yours with a dial indicator.

 

[95GST]

195 PSI is possible with some carbon buildups. Look for consistency across the cylinders. You can try to use another compression tester also, I keep two testers myself so I can double check if I wanted.

 

[Turbo Guru]

I have no dial indicator for such a measurement. As for the second compression test once I get my head to seal I will try a different tester. As for carbon buildup their is just enough to make the piston face to appear black but not enough to affect compression. What exactly are the differences between 1G an 2G pistons? Is the dish the same with a taller overall piston?

 

[boost]

Yes dsm pistons all have the same writing on top. From the last picture you have it looks like theyre 95+. The 90-94 pistons are 7.8 to 1 compression ratio. You said they were almost flat top and 90-94 have quite a deep dish that i dont think you could miss. I have 95s in my 92 you will have about 190+psi that is normal with this modification. Just because you have high compression doesnt mean you have these pistons. Could be carbon buildup.

 

[boost]

Yes dsm pistons all have the same writing on top. From the last picture you have it looks like theyre 95+. The 90-94 pistons are 7.8 to 1 compression ratio. You said they were almost flat top and 90-94 have quite a deep dish that i dont think you could miss. I have 95s in my 92 you will have about 190+psi that is normal with this modification. Just because you have high compression doesnt mean you have these pistons. Could be carbon buildup.

 

[boost]

Yes dsm pistons all have the same writing on top. From the last picture you have it looks like theyre 95+. The 90-94 pistons are 7.8 to 1 compression ratio. You said they were almost flat top and 90-94 have quite a deep dish that i dont think you could miss. I have 95s in my 92 you will have about 190+psi that is normal with this modification. Just because you have high compression doesnt mean you have these pistons. Could be carbon buildup.

 

[boost]

Yes dsm pistons all have the same writing on top. From the last picture you have it looks like theyre 95+. The 90-94 pistons are 7.8 to 1 compression ratio. You said they were almost flat top and 90-94 have quite a deep dish that i dont think you could miss. I have 95s in my 92 you will have about 190+psi that is normal with this modification. Just because you have high compression doesnt mean you have these pistons. Could be carbon buildup.