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'Kurled' compression ring

E

exercise

Well Known Member
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What would cause the 'knurling' on this center ring of the #1Millennium Cylinder? About 100 hours on the professionally rebuilt Lycoming E2A 160 hp and always run LOP with mo gas. Synthetic oil changes prior 40 hours. Blackstone reports fine. Borescopes decent with slight scoring. RV4 so cool cht's. Other three Millennium cylinder compression tests always showed 78 or 79. This #1 cylinder showed 78/76/70/66 and the consensus was to pull it in case the decline was due to a cracked or broken ring. The highly regarded local engine shop measured the cylinder at .005" out of round. They had not seen a ring like this before. No reply from Superior so far.ring.jpg
 
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exercise said:
What would cause the 'knurling' on this center ring of the #1Millennium Cylinder? About 100 hours on the professionally rebuilt Lycoming E2A 160 hp and always run LOP with mo gas. Synthetic oil changes prior 40 hours. Blackstone reports fine. Borescopes decent with slight scoring. RV4 so cool cht's. Other three Millennium cylinder compression tests always showed 78 or 79. This #1 cylinder showed 78/76/70/66 and the consensus was to pull it in case the decline was due to a cracked or broken ring. The highly regarded local engine shop measured the cylinder at .005" out of round. They had not seen a ring like this before. No reply from Superior so far.
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My speculation is that it was a manufacturing defect and was installed that way. Notice the very top of the ring has worn smooth from riding up and down the cylinder wall. It is likely misshaped and that is why the contact patch is so small. Highly unlikely that was created while running in the cylinder imho.

Likely the installer just assumed all the rings were good and never examined the surfaces. That said, superior rings generally need to be filled down a bit, so someone probably should have caught it while doing that.
 
Another builder suggested that that ring was probably a manufacturing defect that went unnoticed by the builder(and me) while we assembled the four new cylinders. He did have to shave a few of the new rings to tolerance.
 
Bore is 0.005" out of round, which means rings can't rotate as they wear to the out-of-round cylinder. Weird wear patterns result when rings quit rotating. Inadequate cooling causes cylinders to go out-of-round.
 
drinkwater said:
Is that seriously a thing that needs to be done? Are you referring to the ring gap, or is it common for there to be defects around the circumference that need to be filed?
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Yes, for superior. And yes referring to the ring gap. Outside edges are done ath the factory, but stuff happens and you end up with the pic above. I believe they come out of the mold looking like that and then go to a surface grinder to clean them up. That one just missed that step.. Most cylinders have a choke at the top and the tolerances are quite loose, so they send the rings a bit oversized and it is up to the installer to measure and size them. Lycoming has tighter tolerances and sends the rings sized. Not sure what cont does.
 
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