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Discussion Starter · #1 ·
Just wondering what an experienced engine guy would think. I just tore down the 73 350 small block that was in my 71 chevelle. It had low compression on 1,3,5 and 7 (<100). All four of these pistons are cracked between the two compression rings and pieces fell out. Would low oil or overheating cause this? Does this have something to do with the direction of coolant or oil flow?? 2,4,6,8 pistons look fine and had good compression (>200). Any ideas for a rookie engine builder??
 

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Hmmm...I hope Bill K can answer this - I really can't remember ever seeing or hearing of anything like this.

My only thought is that this was a production line rebuilt engine, with one guy on each side of engine, and that somehow the #1,3,5,7 piston guy messed up! Either he damaged parts during installation or didn't get the right ring end gaps.

Question: do the pistons from the pass side match the drivers side pistons? Not only in style and brand, but size also. Speaking of size, do you think that the piston rings were for the same size pistons on both sides? Did it look like the ring end gaps were set in the right relationship from side to side - the driver's side ring gaps are set 180 degrees opposite of the passenger side.

Dunno really, but I'm curious what others have to say.

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"Bomber" '67 El Camino, Beater comes back to life.
Was 350/TH350 14.90 @ 93mph, 360,000+ miles on car
Now 406 roller, 340rwhp, more hp coming, 3.08 gears
Street radials, left in drive, 13.20 [email protected] mph
 

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Gibs,
The type of damage that you describe is caused by detonation 99% of the time. Over heating will also cause it. What happens is the piston and rings get so hot that they expand to the point that the rings actually bind up in the bore. The piston keeps trying to move and the ring lands break. I bet if you look at the ends of the rings that are still in one piece, they will be very shiney, indicating that they have been butting against each other.
Hope this helps,

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

1971 Heavy Chevy - original owner
Team Chevelle #100
 

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Quite a few years ago I had a similar experience.I had put a 350 in a 74 vega,I guess I turned it up a little too much before getting it warm enough.I had 4 of 8 pistons do the exact same thing.I lowered the compression with a dished piston instead of the flattop and it actually ran stronger.Maybe it was the compression.I was only 17 at the time so I was just a beginner motorhead.I feel like in my situation then was bad gas for the compression that I had.Never did investigate it much.But I sprayed for mosquitoes for 2 weeks after that till I pulled everything apart.The oil companies loved me then.


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John 67SS
ACES #2887
Team Chevelle Gold #127
 

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Discussion Starter · #5 ·
Another guy at a local engine shop said a leaky intake could do this?? It made a little sense since the engine had double intake gaskets on both banks. The pistons look the same size & type on both banks. I'm checking the ring end gaps and measuring the pistons, bore, etc. this weekend. I'm checking the heads & block to make sure the match up OK. The intake is a holley contender.
 
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