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

[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.

[Trident]

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.

And I've been resisting the urge to start a urinating contest. As for a gap, you won't see one... but you will create areas of differing surface pressure on the bore.

See below:

Ring Gaps: Mercury 44, 40 and 30 cu. in. fours.

I absolutely do not agree with oversize rings with the gap filed to fit… Yes, I know that was Harry’s mantra but I'll say it again, I absolutely do not agree with oversize rings with the gap filed to fit.

With oversized rings, I feel that in an effort to solve one problem, you create another…

First off, rule of thumb is gap should be 2 ½ times bore dimension, in thousandths. Then, remember our Mercury pistons with their heavy section deflectors hold a lot of heat, so these pistons may need more ring gap clearance than other designs... I think .004” that some recommend is too tight under heat… I’d love .008”. No less than .007”

And an oversize ring squooshed (technical term) into a tighter bore distorts, putting three pressure points on the distorted ring and creates two areas of lesser ring tension pressure on the bore. You are smart enough to figure out where those light and tight spots are, I’m betting. Any reason you’d prefer less sealing at the port areas?

Mercury stock rings are approx. .012” gap. That’s looser than I’d like, so I pick the tightest for top rings. And for the ‘leakdown’, I don’t worry about it, as I get 140 # at roping speed which is what, 3 rpm?

What’s the leakdown at 7200 rpm?

Lets do a thought experiment here…

That too big ring gap sticks out what, say .007” piston clearance (cold), so say 3 ½ thou on a side, so the 'extra' gap is 3 ½ X 4 thou (.012” - .008” that I’d like). That’s a tiny, tiny gap. At 7200 rpm, we fool ourselves using RPM, should be RPS to be more relevant, that’s 120 times UP AND DOWN per second, and only roughly half the travel up and down is under compression or combustion pressure, when ports are closed. And that tiny, tiny leak has a second and third line of defense, the #2 ring and #3 ring… How much leakdown can that be? A gnat fart?

And that gap is smaller yet under heat, running, and with lots of oil (I run 8 : 1, BTW)

I’d rather have a round perfect ring fit to the bore, than .004” less gap with ring distortion. And, with possible ring gap binding from being too tight... I do see a lot of guys running really tight ring gaps trashing pistons regularly...

Never had that in my motors.

All my UIM record motors and National Championship motors ran 3 Mercury OEM correct bore size rings. The one thing I did, early on, was bevel the bottom only of the bottom ring(s). Then I quit doing that. Now I select the tightest rings for the top and install all 12 right out of the box. On 44’s with 2 Keystone rings, I take ‘em right out of the box and make sure to put them right side up.

Hope this helps.

Jerry

[zul8tr]

And I've been resisting the urge to start a urinating contest. As for a gap, you won't see one... but you will create areas of differing surface pressure on the bore.

See below:

Ring Gaps: Mercury 44, 40 and 30 cu. in. fours.

I absolutely do not agree with oversize rings with the gap filed to fit… Yes, I know that was Harry’s mantra but I'll say it again, I absolutely do not agree with oversize rings with the gap filed to fit.

With oversized rings, I feel that in an effort to solve one problem, you create another…

First off, rule of thumb is gap should be 2 ½ times bore dimension, in thousandths. Then, remember our Mercury pistons with their heavy section deflectors hold a lot of heat, so these pistons may need more ring gap clearance than other designs... I think .004” that some recommend is too tight under heat… I’d love .008”. No less than .007”

And an oversize ring squooshed (technical term) into a tighter bore distorts, putting three pressure points on the distorted ring and creates two areas of lesser ring tension pressure on the bore. You are smart enough to figure out where those light and tight spots are, I’m betting. Any reason you’d prefer less sealing at the port areas?

Mercury stock rings are approx. .012” gap. That’s looser than I’d like, so I pick the tightest for top rings. And for the ‘leakdown’, I don’t worry about it, as I get 140 # at roping speed which is what, 3 rpm?

What’s the leakdown at 7200 rpm?

Lets do a thought experiment here…

That too big ring gap sticks out what, say .007” piston clearance (cold), so say 3 ½ thou on a side, so the 'extra' gap is 3 ½ X 4 thou (.012” - .008” that I’d like). That’s a tiny, tiny gap. At 7200 rpm, we fool ourselves using RPM, should be RPS to be more relevant, that’s 120 times UP AND DOWN per second, and only roughly half the travel up and down is under compression or combustion pressure, when ports are closed. And that tiny, tiny leak has a second and third line of defense, the #2 ring and #3 ring… How much leakdown can that be? A gnat fart?

And that gap is smaller yet under heat, running, and with lots of oil (I run 8 : 1, BTW)

I’d rather have a round perfect ring fit to the bore, than .004” less gap with ring distortion. And, with possible ring gap binding from being too tight... I do see a lot of guys running really tight ring gaps trashing pistons regularly...

Never had that in my motors.

All my UIM record motors and National Championship motors ran 3 Mercury OEM correct bore size rings. The one thing I did, early on, was bevel the bottom only of the bottom ring(s). Then I quit doing that. Now I select the tightest rings for the top and install all 12 right out of the box. On 44’s with 2 Keystone rings, I take ‘em right out of the box and make sure to put them right side up.

Hope this helps.

Jerry

That should sum it up.
So Brinkman didn't always have the answers.
Per your rule, on 22 ci Mercs and also the 44's the 2.5 x bore = ring gap in thousands is on the low side for your .007 min., but .008 preferred.

Thanks for the info

[Trident]

Harry had an answer. Maybe right, maybe not, but the beauty of Mod is there can be more than one right answer. On this point, I disagree with him.

But also realize that's a theoretical rule of thumb, the 2 1/2 times bore thing... Note, I also said these heavy section deflector pistons may really need more gap because of heat build up. I didn't have a way to get a tighter gap without using an oversize ring, so I don't really know what is the 'perfect' gap.

In winning motors, no failures is perfect in my book. If it ain't broke, don't fix it.

I'm fine with stock Mercury rings. I still say any extra leakdown is insignificant, at temperature, at speed. Those clearances are far different than what we measure, cold, on the bench.

Jerry

[Tim Weber]

I have to agree with Jerry.

Another famous builder of mod and pro engines felt the same way. Lon Stevens told me not to worry all that about ring gap. He told me that the piston is going up and down so fast, how are you going to measure the difference. He was more concerned in sticking the motor and broken rings.

Tim

[daveswaves]

Thanks Guys, this engine has been a problem for Jeff.

[Fastjeff57]

But only at low speed. It goes like stink above 5,000 rpm. Heck; I can live with that.

Jeff

[Ron Hill]

Harry had an answer. Maybe right, maybe not, but the beauty of Mod is there can be more than one right answer. On this point, I disagree with him.

But also realize that's a theoretical rule of thumb, the 2 1/2 times bore thing... Note, I also said these heavy section deflector pistons may really need more gap because of heat build up. I didn't have a way to get a tighter gap without using an oversize ring, so I don't really know what is the 'perfect' gap.

In winning motors, no failures is perfect in my book. If it ain't broke, don't fix it.

I'm fine with stock Mercury rings. I still say any extra leakdown is insignificant, at temperature, at speed. Those clearances are far different than what we measure, cold, on the bench.

Jerry

I don't wish to High Jack this thread, but I have a few questions and thoughts. Harry Brinkman and I may have never met fact to face, but he sold 55-H "dead" rings that my dad liked. Over the years, my dad probably machined 200 pistons from castings. It seemed he was always careful to not make the ring grove too deep (Whispered a "Back Gap" in the old days). He also had some a theory for every inch of bore, so many thousandths of ring gap.

I do know my dad was a fanatic about cylinder bore being exactly to MERCURY specs, and once the bore was over like .002, he'd change my blocks.

Once the rule in APBA Stock was changed to any ring, my dad made aluminum rings for the bottom two rings. These rings were the depth of the ring grove and they just butted to the piston pin.

Trident, did you ever run aluminum rings on the bottom two? If you did what was your results?

So, the 44's now have "L" rings???? Shows how long it has been since I took a motor apart. Notice I said, "Take apart" as my dad always put them together.

How much break in time????