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Discussion Starter · #1 ·
Ok car is a 94 2.0L 8v fully built. Ross pistons.. We had it up on the dyno last week and 3 pulls before the last it started knockin it sounded like. Drove it to waterfest and came back 6 quarts of oil later and pulled the motor apart. 2 pistons had broken compression rings one was # 4. #4 piston was smeered front and back real bad below the oil rings. Rings broke at the ends where they come together only on one side. Cylinder 1 -3 all had 140psi of compression and #4 only had 120psi.
My ? is why did # 4 knock so bad and smeer severely and the other piston with the broken ring didn't and still had good compression. I'm getting ready to build the motor again going with CP coated pistons .020 bigger and have the block machined for proper clearence.
When i first built the motor i felt like there was to much clearence between the piston and the wall, but my bud said it was ok. Well, the rings didn't seat that first time. So we went with bigger rings i think and they took, but now a while later they're broke.. If i remember correctly when i was filing the rings and i would put one in the cylinder it would overlap allmost an 1/8 of an inch so i had to file quiet a bit. I used a power dremel to file allso. Could i have got the ends of the rings to hot and changed the structure at the ends??

O yeah what clearence is everyone running? Going to be making around 350 whp and pushing around 21psi maybe more in the future when the motor is built right..
 

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Re: #4 piston was slappin and burning oil. Why?? (Vdubin474)

dude u should never have to file piston rings down... bad idea maybe ur block was over bored and thats what caused everything to get fed up next motor u build check the piston to wall clearance the tool is like 9 bucks http://****************.com/smile/emthup.gif
 

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Re: #4 piston was slappin and burning oil. Why?? (2slo4me)

Not true about filing rings down. It is standard operating prodedure on a lot of build ups. That is why machine shops have special tools to file down the rings. If you have to do that again, get the proper tool (about $25) or just use a flat file.
I am not sure what your clearances were (rings and piston-cylinder) but the next time you build it up, be more careful and attentive of them. CP Pistons will be able to tell you what you should be shooting for given your HP goals.
Quote, originally posted by 2slo4me »
dude u should never have to file piston rings down... bad idea maybe ur block was over bored and thats what caused everything to get fed up next motor u build check the piston to wall clearance the tool is like 9 bucks http://****************.com/smile/emthup.gif
 

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Discussion Starter · #5 ·
Re: #4 piston was slappin and burning oil. Why?? (vfarren)

I checked the piston to wall clearence it was .003 or three thousandths.
I'm going to run 35 thousandths this time, but still not sure wht caused the failure. I'm guessing it was the ring gap and they where touchin.
 

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Re: #4 piston was slappin and burning oil. Why?? (Jefnes3)

maybe the ring gaps were too small
that'll bind and break rings all day when you get some extra heat into them... Some sketchy tuning will burn pistons all day, too.
 

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Discussion Starter · #8 ·
Re: #4 piston was slappin and burning oil. Why?? (jwatts)

Pistons are fine except #4. The 2 rings broke at the ends where yes they probably rubbed. The 2 ringsd were in 2 different cylinders, but #4 had hella damage and the other didn't. The top of #4 piston was fine the front and back were smeared like it tried to seize. The other piston with the broken ring was fine. Don't know why exactly, but it was.
I'm guessin the seizein came from the hot gasses explodin through the ring burin up the lube on the cylinder wall. Question is why the front and back of the piston are messed up and the other piston with the broken ring is fine?
Just the compression rings where busted none of the others.
 
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