Broken Piston Ring Found During Tear Down

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Vertex_Jeff

Vertex_Jeff

Undocumented Mopar Guy
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Hey guys, I tore down my 440 yesterday for a trip to the machine shop over the off season. A couple weeks ago at the track, I broke a rocker arm and bent a push rod on #6 intake. Because of the push rod beating the crap out of stuff, I had aluminum dust in the top end, so that is what prompted me to do the tear down.

During the tear down, I found that I had a broken ring on #8 cylinder. It was the bottom ring. The broken piece must have stayed in the grooves all this time, because the walls in that cylinder were not scratched to hell. This find was interesting, and un-expected. The pistons are 30 over KB hypers, and heavy-*** LY rods. These had 2 seasons on them, with about 60 drag strip passes, and about 5,000 street miles. When racing, I shift @ 6,000 rpm. My Cuda weighs 3600 with me in it, and we were running 11.1's consistently in the quarter. Top end was Trick Flow 240's, Howards hydraulic roller, Weiand tunnel ram, dual quads.

I'm building back with a stroker kit - so i wont be re-using this rotating assembly again.

However, I AM curious how a ring breaks like this? I have never had a ring break before.



broken ring.jpg
 
Wow, that sucks but I wish I could have seen how it happened. My guess if it's a cast ring that it was stressed by the install, but I'm not sure.
I've only seen rings eat themselves from butting together.
What are your plans for the new stroker ?
 
KB (hypereutectic) pistons require wider than normal ring end gaps. Perhaps that one was a bit on the tight side or running hotter than the others and butted long enough to break. Perhaps some pre-ignition, detonation? Broke on installation? No cylinder wall scuffing is interesting.
 
I always run the nitrous spec ring gaps on KB pistons even when running naturally aspirated. You cannot be too careful with those.
 
Years ago (1977ish) I had my 361 big block rebuilt. The bottom ring on one piston was found to be broken in half but did not score the cylinder wall. The engine had been running just fine.
 
Vertex_Jeff said:
Hey guys, I tore down my 440 yesterday for a trip to the machine shop over the off season. A couple weeks ago at the track, I broke a rocker arm and bent a push rod on #6 intake. Because of the push rod beating the crap out of stuff, I had aluminum dust in the top end, so that is what prompted me to do the tear down.

During the tear down, I found that I had a broken ring on #8 cylinder. It was the bottom ring. The broken piece must have stayed in the grooves all this time, because the walls in that cylinder were not scratched to hell. This find was interesting, and un-expected. The pistons are 30 over KB hypers, and heavy-*** LY rods. These had 2 seasons on them, with about 60 drag strip passes, and about 5,000 street miles. When racing, I shift @ 6,000 rpm. My Cuda weighs 3600 with me in it, and we were running 11.1's consistently in the quarter. Top end was Trick Flow 240's, Howards hydraulic roller, Weiand tunnel ram, dual quads.

I'm building back with a stroker kit - so i wont be re-using this rotating assembly again.

However, I AM curious how a ring breaks like this? I have never had a ring break before.



View attachment 1716157562
Click to expand...


Cheap garbage gas, detonation, improper installation, type of piston. Could be any of the above.
 
I always run 93 or at the very least 91 octane in it, so I dont think it was bad gas. (Although, on Rocky Mountain Race Week, some of the gas stations in the middle of nowhere are a little sketchy!)

I can absolutely believe it happened at assembly! I had a well known, well respected, shop in east central Indiana do a refresh on the short block back in 2020. They did a hone, re-ring and bearing on it. **** happens - but it lasted 2 seasons with me kicking it's ***, so i cant be upset.
 
When I rebuilt the first 340 in my 65 Barracuda, I found five broken rings when I took the motor apart. It ran well (just a street car daily driver), but did have a lot of blowby. The motor had well over 100K on it (had the car since 68, 340 since 73), so I think it was high miles and repeated high rpms that did the trick. Have not encountered any broke rings since.
 
I would NEVER bounce the motor off of the rev limiter while screwing around with my buddies doing burnouts...... NEVER I say!
 
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The engine sure revs up quickly.
Maybe the broken piston ring had something to do with it!
Don't let Uncle Tony see this clip, or he'll start a You Tube frenzy about the racers back in the day that used broken piston rings for an advantage at the drag strip because of the lower friction...
 
I just found the same thing with my 440 that I dropped a valve in when I tore it apart. I did not assemble the engine, it came in the car I bought. Looks like the ring rode along and did not kill the cyl. wall, amazing !
 
Dartnut said:
The engine sure revs up quickly.
Maybe the broken piston ring had something to do with it!
Don't let Uncle Tony see this clip, or he'll start a You Tube frenzy about the racers back in the day that used broken piston rings for an advantage at the drag strip because of the lower friction...
Click to expand...
I think I remember that UT was going to do a dyno run using just the top ring and oil control rings
 
EdsWelding said:
I just found the same thing with my 440 that I dropped a valve in when I tore it apart. I did not assemble the engine, it came in the car I bought. Looks like the ring rode along and did not kill the cyl. wall, amazing !
Click to expand...
I think with no tension and a shitload of oil on the cylinder walls it would not gouge the cylinder wall.

One of the Turbo 2.2's blocks I acquired years ago had 2 top rings snapped. The blow by was huge. Piston crowns were like orange peel due to detonation and sparkplugs has speckels of alumumn.
 
EdsWelding said:
I just found the same thing with my 440 that I dropped a valve in when I tore it apart. I did not assemble the engine, it came in the car I bought. Looks like the ring rode along and did not kill the cyl. wall, amazing !
Click to expand...
Could be the latest trend in piston ring technology!!!

I can't wait until we have Bluetooth compression rings.
 
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