Broken ring question

[Rodsrsr]

I'm running a US spec stock 3.2 with a turbo set at .5 bar. I recently noticed a small amount of smoke puffing from the oil tank so I did some investigating and determined that #5 cylinder was low on compression. (110 lbs vs the rest @ 150lbs) I suspected a broken ring and after tearing it down my suspicions were confirmed. The top compression ring on #5 had a very clean break, almost as if someone snapped it in two pieces clean. The ring lands all spec out and all of the other rings are fine. I believe a dirty injector along with a clogged waste gate vent created an overboost situation which was the cause.

I also can see hone marks on the Mahle cylinders and I do recall being told that the engine was re-ringed when I purchased it. I've already gone through the top end a few years ago, with a complete valve job, 20/21 cams, valve seals and new timing chains/ramps.

My question is what would be the best course of action to fix this? Should I just replace the one ring? all rings on #5 or re-ring all 6? The pistons and cylinders all spec out even the ring lands on # 5.

Being that only one ring broke on #5 is it logical to assume that the remaining rings on the other pistons/cylinders may have been weakened which is why I'm wondering if I should re-ring it again. I hope that makes sense and thanks in advance.

[dannobee]

What caused the ring to break? Assuming that it wasn't broken on the installation.

If it were mine, you'd bet that I'd be pulling all of the cylinders off and checking the ring gap. At the very least. Tight ring gaps and boost are a good way to break rings or pull the whole top of the piston off.

[Rodsrsr]

The rings were installed correctly and I've had the motor for years with all 6 cylinders reading around 150lbs. I knew something was wrong when I noticed smoke puffing from the oil tank during a routine oil level check, which is what prompted me to tear it down.

[Richey]

New rings on used pistons wears the ring groove exponentially when the rings are breaking in . I've been told the high end of the ring groove play is in reality the wear limit . I do not recommend new rings , I think if you need new rings you need new P's and C's , unfotunately that's the reality . I think your engine supports this theory .

[911pcars]

Originally Posted by dannobee

What caused the ring to break? Assuming that it wasn't broken on the installation.

If it were mine, you'd bet that I'd be pulling all of the cylinders off and checking the ring gap. At the very least. Tight ring gaps and boost are a good way to break rings or pull the whole top of the piston off.

Agree. If insufficient end gap and/or excessive boost pressure, not good for extended ring/piston life.

As in any rebuilding situation, careful inspection is mandatory to ensure a good rebuild result. If the ring lands are worn, especially on a turbo running high boost (and borderline detonation), that could be a good reason to consider replacement.

Sherwood

[Eagledriver]

Detonation most likely caused the broken ring. No reason to mess with anything else. Just replace the broken ring and make sure to keep engine parameters safe. (Boost, octane, ignition advance).

-Andy

[Rodsrsr]

Thank you everyone for the feedback.