got my motor apart and......
Thread Starter
Instructor
Joined: Dec 2002
Posts: 115
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From: Arlington tx
got my motor apart and......
I got my 350 out of my vette this last weekend and I just finished stripping it down to get ready to go to the machine shop and when I started popping pistons out I found that EVERY piston on the pass. side (2,4,6,8) had cracked top rings. One piston had the top ring fall out in 2 pieces another had three and the other two the top ring was completly shattered. What would cause this? I just bought the car 2 weeks ago and I am in the process of fixing it up and the deeper I get into it the more work I foind for myself to do :mad . Thanks in advance.
Lason
Lason
Le Mans Master
Joined: Aug 2000
Posts: 6,362
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From: Brazos TX
Cruise-In IV Veteran
Cruise-In V Veteran
Re: got my motor apart and...... (lason)
Yep, Twin_Turbo said it. Detonation that was probably caused by oil in the combustion chamber. That can come from the valve guides or (more likely) the rings. I bet the bearings look pretty bad on those particular rods.
Thread Starter
Instructor
Joined: Dec 2002
Posts: 115
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From: Arlington tx
Re: got my motor apart and...... (burners)
The bearings looked worn but they were all worn evenly. Light copper showing in the center of all the rod and main bearings. O well, the pistons look ok but I think I am going to have block bored .030 over so new pistons are already on my list. As far as heads go, I will either have the ones I have rebuilt or go ahead and save my pennies for some trick flows.
Race Director
Joined: Sep 2002
Posts: 10,362
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From: San Diego - Deep Within The State of CONFUSION!
Re: got my motor apart and...... (lason)
Look forward to the results! Congrats on the rebuild project. I've built a LOTTA V-8's and never seen one come apart like your description. Interesting!
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
Re: got my motor apart and...... (lason)
What would cause this?
In a worn engine there will be a ridge on the top of the wall, where the rings don't reach. The rings are also worn, so they are slightly thinner than new. Then someone does a cheapo rebuild with new rings, and the new rings are now slightly thicker. BAM, they hit the ridge and shatter. Happens every time.
Safety Car
Joined: Aug 2001
Posts: 3,687
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From: Waterford Mi
Re: got my motor apart and...... (MARKUS_P)
Keep in mind that GM heads don't have replicable valve guides. If you plan on having the heads reworked, make sure the shop is capable of machining in bronze guides and not just putting new seals on the valves. I would save up "the pennies" and replace them.
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Safety Car
Joined: Oct 2000
Posts: 4,080
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From: Allen TX
Re: got my motor apart and...... (lason)
I agree with Zwede. If its just the rings and there is no evidence of the ring lands in the pistons also cracking, then he's right on track.
Detonation that is bad enough to bust the rings will also typically cause damage/cracks in the ring lands as well...been there, done that. ;) It also takes some _serious_ compression to do this. A little pinging going uphill with some bad gas in the tank isn't gonna crack all the rings.
When I've had issues it was too much timing and 14psi of boost. :p: Very, very high combustion pressure and temps.
Detonation that is bad enough to bust the rings will also typically cause damage/cracks in the ring lands as well...been there, done that. ;) It also takes some _serious_ compression to do this. A little pinging going uphill with some bad gas in the tank isn't gonna crack all the rings.
When I've had issues it was too much timing and 14psi of boost. :p: Very, very high combustion pressure and temps.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
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From: Unreconstructed, South Carolina
Re: got my motor apart and...... (john's '81 mouse)
The very top of bore (about 1/8"-1/4" in depth) doesn't wear. If the bore has a lotta miles on it ... the top of bore has a ridge. If you knock the pistons out without first removing ridge ... you'll often crack the rings (new rings or old rings, no matter).
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
Re: got my motor apart and...... (lason)
Another cause along the same lines, particularly with an older engine that has not been apart for a while (as I suspect with yours), is high RPM with a lot of carbon build-up on the ridge. The bearing wear you describe bears this out. Think of the guy that buys a car from a little old man and then "blows it out" after he gets it - more like "blows it up"! :D
Hans
Hans
Thread Starter
Instructor
Joined: Dec 2002
Posts: 115
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From: Arlington tx
Re: got my motor apart and...... (Wrencher)
here are soem pictures I just took..
the second pic is hard to see but believe me the ring lands on the pistons are fine (although I am going to use new pistons)
the second pic is hard to see but believe me the ring lands on the pistons are fine (although I am going to use new pistons)
Safety Car
Joined: Feb 2002
Posts: 3,556
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From: Seattle WA
Re: got my motor apart and...... (jackson)
Lason, you get more Kudos. first you jump in to tearing down the body, now the motor? and fast at that!
im guessing the ridge suggestion too. in the engine i was assigned to rebuild in class last year, we noticed a pretty big ridge on some of the cylinders. the motor was fairly low-mileage (about 30,000) and we couldnt figgure out why someone junked it. until we got the pistons out and the rings fell apart like yours. instant blowby / oil consumption problem.
im guessing the ridge suggestion too. in the engine i was assigned to rebuild in class last year, we noticed a pretty big ridge on some of the cylinders. the motor was fairly low-mileage (about 30,000) and we couldnt figgure out why someone junked it. until we got the pistons out and the rings fell apart like yours. instant blowby / oil consumption problem.