Ring Wear Question

[Fastjeff57]

Several times now I put new rings in this troublesome motor I've been messing with, and each time after I pull her down again the rings have about an 1/8 inch gap. They went in there with about .012 inch gap, yet...

Is this normal after rings break in? The compression readings are holding at a reasonable level (and even increased a bit with running). In every case, the motor had less than a few hours running, and not at WOT for more than a few seconds at a time. Oil level mixture 30:1 initially down to 45:1 after break in.

Jeff

[25XS]

Were they oversize rings filed to fit standard bore?

[zul8tr]

Jeff

What difference in bore diameter are you measuring. To go from a gap of 0.012" to 0.125 is an increase of 0.113" in ring circumference. That would mean an increase in bore diameter of about 0.113/Pi = 0.036", way huge? Are you getting that same increased ring gap in all the locations in the cylinder you measure?

Strange that so much wear occurred with that oil mix?

What kind of rings are you using, OEM NOS, or--?
Maybe they are made in China?

[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

[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.

[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.