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Broken piston rings
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Have a slightly worked a12 with a cam and h89 head and this is the second time i have broken the top compression rings.

The first time i suspect due to running to much timing. But when replaced the rings i put the timing back to factory 8 degrees and i just took the engine apart to put in some flat top pistons and all rings where good except cylinder 4 top ring was broken again.

Is this caused by detonation? Engine revs to 7500-8000rpm every know and then do i have to run less total timing then factory for these rpms?

Realy want to figure this out before putting the flat tops in and upping compression.

Posted on: 12/14 11:08
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Re: Broken piston rings
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Take a look at a few other things, it's possible that it broke during installation as in your ring compressor didn't fully compress the rings and the ring caught on the lip and got broken while being installed. Another thing to look at is if there is a ring ridge in the cylinder walls, Nissan blocks are hard and don't usually need a rebore from wear, but I have seen it happen on occasion. And as a last thought if the rings are too large for the bore as in insufficient gap when installed will cause rings to break, check the ring gap before installing them on the piston. Good luck.

Posted on: 12/14 16:12
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Re: Broken piston rings
No life (a.k.a. DattoMaster)
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I've run 12-1 compression & 8200 rpm in the A15 and 11.8 compression & 8600 rpm in the A12. I've never had a ring break.

Something isn't right; either the ring end gaps or as rgrinder mentioned it snagged when the piston was installed.

I'm also not using any fancy rings just standard Hastings or other known brands.

Posted on: 12/15 0:25
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Re: Broken piston rings
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Bore has no lip and i checked ring gap every time i had it apart and was always on the higher end of the spec, installation is not the issue either.

I think it may be detonation which is realy hard to hear over the engine and exhaust.

Rallytwit. How much total timing did you run with that much compression?

Once im done woth this new build I will stick to 98 octane to be on the safe side.

Maybe 30 degrees of timing would be safer than 32?

Compression will be around the 10.1 mark.

Posted on: 12/15 5:19
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Re: Broken piston rings
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Is there any obvious damage to to piston it's self? Detonation or preignition will usually cause damage to the piston it's self or the cylinder head before breaking rings.
Are the ring lands deep enough to allow the rings to properly compress? As in are the rings the ones called for by the piston manufacturer, there has been a lot of talk about using pistons for other engines to increase displacement, not a bad idea when you can't get what was once available, but different brands use different engineering specs. I guess what I'm trying to say is that there could be many reasons for a broken ring and detonation isn't the most common, might be time to start to consider looking any and all possibilities.

Posted on: 12/15 15:55
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Re: Broken piston rings
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Is this caused by detonation?

Yes

Posted on: 12/15 21:21
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Re: Broken piston rings
No life (a.k.a. DattoMaster)
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a12dato120y I'm running 38 degrees of total timing but I use 100 octane fuel.

Posted on: 12/15 22:49
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Re: Broken piston rings
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it's hard to hear detonation, so make some detonation cans

btw the first image that comes up there is a broken piston land

Posted on: 12/15 23:16
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Re: Broken piston rings
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Im kind of running out of ideas.

Pistons and all are fine rings go in all the way when fully compressed.

I find it odd that only cylinder 4 did it this time.

Forst time it broke all 4 only top rings which make me think its detonation when this happened i had a weber down draught carburetor on it (34ADM)

Now i have cbr1100 38mm mikuni bike carbs and i have only broken number 4.

But I am starting to wajder if itsnrunning to lean. I will obviosly have to hook up a wide band to verify.

Also there is no damage to pistons at all and all look very good woth no signs of detonation.

Posted on: 12/16 8:14
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Re: Broken piston rings
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OK, I'm not trying to start a pi$$ing contest here, I've spent 40+ years working on cars for a living and I have seen a lot, not everything, no-one could, that said this is based on my experience. Knock, ping, rattle under acceleration, funny noise, pre-ignition, detonation all cause engine damage. Over time you should see erosion of pistons or combustion chamber, broken spark plug porcelain, or a combination of the above. Detonation does not just cause a broken ring without other damage being obvious. Like I stated before maybe you need to take a good look at everything and not be quick to blame it on one thing, and it might be a good idea to get someone else to look at it also, most times two or more pairs of eyes are better than one. IF you still come to the same conclusion here are a few things to consider, richen up the carbs to see if it goes away, a "wet" mixture is less prone to pre-ignition because it's cooler. Try a step or two cooler spark plug, incorrect spark plug heat range can and usually will cause problems if your not sure what to use ask around to see what others are using, and finally look for vacuum leaks, they will cause a lean condition in 1 or 2 cylinders. Again, GOOD LUCK.

Posted on: 12/16 16:50
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