Pistons wiggle? huh...

[AjWit]

As some of you know, i bought a 90 gst recently that had no compression. I just got the head off today and boy oh boy, i think i put my finger on the compression leak. Each of the pistons, have a slight wiggle side to side, and to all sides, not just one way or the other. As you push it to one side, you can actually see the ring still pressed against the cylinder wall. I can get pictures or video if someone wants to see.

Ive never seen this before. My first reaction to this was, "are those pistons a smaller bore than the cylinders?" And im still thinking that. I have another assembled block in my basement and those pistons fit nice and snug, with ZERO wiggle.

Two things:
Can someone shed some light on this 'piston wiggle'?
-and-
Now that the heads off, how much more work will it take to remove the block but leave the tranny in the car?

 

[jdunbar10]

wow
sounds like ## in a shit possition


well first take the tranny out you will have to remover it anyways no matter what

and no u should have no gaps like that in ## block thats just messed
full rebuild or buy a used motor is really the only way to go

 

[AjWit]

You can now see the madness on youtube. WTF is up with this.
YouTube - Piston Wiggle in my DSM

 

[aspekt9]

Had the same issue with a buddies motor I took out of his car to rebuild for mine. Whoever had put it back together just threw everything in. The PTW clearance wasn't checked (it was too large) the ring end gaps weren't measured or filed correctly (they were too large) this led to the same issue that you have including the low compression.

If you're removing the motor, you mine as well take the tranny out with it, you can't really leave the transmission in the car as it's only held by one mount.

 

[Killa_dsm]

Yeah that definitely is not normal. Maybe the motor was bored and the previous owner didn't get pistons for the bore size.

 

[AjWit]

Thanks guys. Thats kinda what i was thinking, to both of your posts. Looks like ill be pulling out my first block and re-doing it all the right way.

 

[beating4g63s]

I'm thinking the previous owner had the block bored, possibly even bought over bored piston rings, and left the stock pistons in there. thats kinda funny in a way....

 

[EclipticalGS]

I thought you may have been exaggerating, but WTF?

Who doesnt spec wall clearances and ring end gaps when assembling? I just don't understand things sometimes?

Me and a friend disassembled a knocking motor that was built by a kid in houghton, way up north, he literally didn't even put rod bearings on his crank/rods. I thought it was a joke when we opened up his crappy b16. He must have been very drunk or just plain old retarded.

That guy coulda built that motor and jsut thought when he bored it, he could just throw some thicker rings in...I mean, ive done this with lawnmowers...but, once again, Lawn Mower.

 

[my98gsx]

ok this video looks all too familiar. This was the same problem i had with my old black last year. Once i removed the pistons i saw that the skirts were damaged. I sent them back to weisco. They told me that it was one of two possible problems. One being the bore might have been improper for the piston causing pre-mature wear on the piston skirt. Or two being i ran too rich and washed the cylenders down, not having the proper lubrication on the cylender walls against wear. Either way my engine was .040 over already so i just went with a new short block from slowboy. Good luck man i know what your going through...

 

[92_6bolt_1290]

before that video, i would have thaught high miles would be the cause but wow thats screwed up man...you can still see copper spray so that engine wasn't rebuilt too long ago before you got it because most of the copper spray just burns up if it gets on the pistons so whoever had this car before you must have had a bad misfire in their head so its probably a good thing you have the car now.

 

[AjWit]

Thanks guys. I was almost in tears reading this, haha. How stupid can you be?! If i borrow a friends multimeter, would i be able to check the bore size of the cylinders? I mean, the cylinders still have a fresh cross-hatching in them. Id say theres under 100 miles on this F'ed up rebuild. Oh well, i get more experience with swapping blocks out. Doesnt bother me, im still happy with this purchase.

 

[4g63thermal]

When i bought my shell it came with a block in it that had the same problem i was like WTF how does this happen.... freind of mine who owns a machine shop say that the cylinders werent round from wear and thats what caused the play

 

[Calan]

If i borrow a friends multimeter, would i be able to check the bore size of the cylinders?

Ummm... what?

My multimeters measure current, voltage, and resistance.

 

[velocitysport31]

what was the compression before you tore it down...Your going to have some movement with in the pistons.

 

[ineedagsx]

btw that is a 2g exhaust manifold, and i second how would you use a multimeter to check bore?

 

[cruisintalonawd]

Ummm... what?

My multimeters measure current, voltage, and resistance.

thats what I was thinking

 

[dsmmatt28]

So the pistons are going to have a little play. Even with a freshly rebuilt motor.
This is way to much play. How do the cylinder walls look? You will probably have some sore of scoring. Run you finger nail across the walls if you feel any deep scrapes etc etc.. The block will need to be re bored and over size pistons will be needed. If the motor was already rebuilt. The block will need to taken to the machine shop to make sure there is enough to be bored over still.

 

[EclipticalGS]

Ummm... what?

My multimeters measure current, voltage, and resistance.

Dont forget amperage and continuity

No I think he meant micrometer, but still, get a bore gauge or some vernier calipers, but then again, vernier calipers wont tell you if the cylinders are ovaled.

 

[Calan]

Dont forget amperage and continuity

Well, amperage = current. But I'll give you continuity as separate from resistance, since mine does have an aditional diode tester with a go/no-go indicator.

 

[EclipticalGS]

, yeah your right, I just typed too fast, but continuity tests have been my best friend when tucking a harness.

 

[Long Duk Dong]

Sounds like the rings could be collapsed or as you stated the pistons could be the wrong size.

 

[AjWit]

to Most of You: Haha sorry guys. Yes, i did NOT mean to type multimeter. I guess i meant micrometer, all i meant was that i know that there is a small tool used to measure that stuff. haha.

to velocitysport31: the compression was sub 50 psi. I think i got to about 30, but that was done at lower than normal temps.

to dsmmatt28: the cylinder walls look great, you can still see the fresh cross hatchings from when it was recently done. no scratches or gouging.

 

[EclipticalGS]

then check the bore, buy some pistons and rings, give the cylinders a slight hone with a deglazing hone, and your good.