Ring Wear Question

[Fastjeff57]

They are .015 oversize cut to fit a standard bore. Genuine Merc rings. All 6 rings wore the same (actually 5--one of them broke on me). I assume the rings wore, not the bore, but I'll re-measure.

So, this is NOT normal after such minor running? It happened twice with the engine (early Merc triple).

Jeff

PS: Thanks for the inputs.

[zul8tr]

If just the rings wore and bore in spec that would mean to me soft metal rings. Other than that it is strange. Post over at JOMS maybe some there have had this, I certainly haven't.

These are 3 ring deflector pistons in that triple for an early Merc.

What wear marks are on the sides of the pistons and the bore? Pics.

Any burrs on the ports and rings are well locked with the pins?

[Fastjeff57]

I had 2 ring slugs in there, and they looked excellent (as did the bores). It appears only the rings are wearing, not the bores. (They are genuine Merc rings, by the way.)

I'm baffled as well. Found a 3 ring piston that I'm going to use in the top cylinder (where the ring broke). The old piston had a bad spot leading to the second ring at the anti-rotation pin (that was not there before I'm fairly sure of). Perhaps that's why the ring broke? Anyways, the compression in the other two holes was good: 140 to 150 regardless of the wide ring gap--so I'm gonna try again.

Thanks for you inputs.

Jeff

[zul8tr]

Persistence required here

[Trident]

Fastjeff57, please drop me a note to tridentracing@new.rr.com

I have some experience with Merc triples and Merc rings.

I have a short document I'd like to send you...

Jerry

[zul8tr]

Jerry

Please post your info here as well so we can all benefit from your expertise. Sure would like to know what strangeness is going on with these rings.

[Fastjeff57]

Me too!

Thanks, Jerry.

Jeff

[Steves Jem]

They are .015 oversize cut to fit a standard bore. Genuine Merc rings. All 6 rings wore the same (actually 5--one of them broke on me). I assume the rings wore, not the bore, but I'll re-measure.

So, this is NOT normal after such minor running? It happened twice with the engine (early Merc triple).

Jeff

PS: Thanks for the inputs.

Hi
Others may disagree but I would say that as you are using 0.015 oversize rings and filing the ring gap that the wear is due to the fact that not all of the outer surface of the rings are touching the bore which would result in the rings wearing excessively where they touch and slight wear where they do not touch. You are trying to fit a large radius into a smaller radius which leaves a gap where they don not touch. I would suggest that you measure the ring depth all the way around and I would bet that it is not uniform but would be consistent with the other rings. I would try to get the standard rings. If you have a spare 0.015 oversize ring I would suggest that you drop it into the bore and run a feller gauge around the circumference to see if there is any gap.

[zul8tr]

Lots of people (usually racers, engine builders) used over sized rings in cylinders to custom fit the gap for top performance. Proper cylinder truing and break in will get a perfect fit. Your suggestion to check the ring depth is a good one and should be done just to eliminate that possibility. The idea to check for a gap around the ring circumference in the bore with a feeler gage is interesting but I doubt if any standard feeler gage would be that thin (thinking if there is a gap it is less than 0.0002", best feeler I have is 0.001"). There is something else going on. Perhaps a very accurate cylinder mic test with a 3 point bore gage (accurate to 0.0002" or there about) would reveal some issues of out of round, taper etc.?

Jerry we are still waiting.

[Fastjeff57]

I did a test with a bright LED light shining through the plug hole and a cardboard disk blocking out the light. Was able to spot light at the gap, but no where else. Tied it with both a standard and .015 oversize ring and couldn't see any light 'leaking' through.

Put the motor together and trailer tested it yesterday. Ran very well and has 130 to 140 compression. Have to wait until Spring to see what she'll do on a boat. Damn Winter!

Thanks for the advice.

Jeff

PS: It's amazing how much easier it is to tune a motor this way vs. on a floating boat! It was able to spin that 17 pitch prop at least 6,000 rpm standing still which is a good sign. Plugs came out way too dark--another good sign.