Ideal ring gaps?

BrianK · Feb 18, 2010

Just measured the old rings I'm replacing - compression ring gaps are .013-.014 and the oil ring scrapers are .020.

There's been some discussion of ring gaps lately, and I understand that modern practice would suggest about an .015ish gap for the top compression ring, a little larger (.016, .017?) for the second compression ring, and...hmm, I don't think anyone's mentioned the scrapers but I do understand .015 is the minimum.

My new rings have virtually NO gap so I have free rein to file the gaps to whatever I want. What do you good folks suggest?

Thanks - Brian

Danno · Feb 18, 2010

Unless you are hopping up the motor, go with the factory-recommended gaps. More power, more heat, larger gaps.

BrianK · Feb 18, 2010

Those are fairly wide ranges, though, hence my question:

Compression rings - .010 to .019

Oil rings - .010 to .040 (!)

Danno · Feb 18, 2010

If you are just re-ringing & honing, I would stay toward the smaller end of the range. New pistons in a fresh bore with skirt clearances at the minimum, I would go larger. More initial friction (and heat) with the former. I would think that the large disparity for the oil scrapers is that their gaps should be offset which would minimize oil passage. I think the last one i did, I put the scraper gaps over the centers of the piston skirts top rear and bottom front and the compression ring gaps 45 degrees each way from the front.

BrianK · Feb 18, 2010

That's what I'm thinking. Maybe shoot for .012 for the compression rings and .015 for the scrapers.

Thanks - Brian

splatt · Feb 19, 2010

Where did you get the larger figures from, 0.019'', from your initial measurement the rings you are replacing don't sound very worn.
0.012'' is good,the thin steel scrapers can easily have around 0.040'' at times, so if you can get 0.015'' would be ok, any reason why the new rings have no gap?thats usually a good sign just to check they are actually correct.
But your biggest question will be......... are you going to put oil on them when you assemble them ,or not.................... that will keep you awake at night now won't it.

Danno · Feb 19, 2010

One drop of oil on each piston skirt is all the lube you need. The rest of the piston-ring-cylinder asembly should be dry. Thee will be plenty of oil in the crankcase after start-up to keep things properly lubed. Oiling the rings and lands will lead to varnish and possible ring sticking.

BrianK · Feb 19, 2010

Mexico Mike was good enough to post the following excerpt from a Norton service bulletin in response to a question I raised:

"Bulletin N69 which covers a wide range of oil consumption issues. The following is copied from the section re pistons and rings:

"11) Piston to Cylinder Tolerances
Examine the bores and pistons to establish that the clear- ances are not excessive. The new Factory produced comp- onents allow for a maximum piston clearance of 0.085mm to O.llOmm (0.0033in. to 0.0043in.) measured at the
bottom of each piston skirt. Piston ring gaps should also be checked. The closed ring gaps in new condition measure 0.254mm to 0.483mm (O.OlOin. to 0.019in.) on the compression rings but 0.254mm to 1.016mm (O.OlOin. to 0.040in.) is permissible on the special scraper rings."

Yeah, those take-off ring gaps don't sound bad at all. Which leads me to think my problem isn't rings at all, but valve guides. No leakdown tester so it's suck it and see for me.

I think the new rings are intentionally shipped with little gap so you can open them up to whatever gap it is you prefer. I'm speculating.

I'm going dry (but for the skirts) this time. Heard so much about this that I just gotta try it - much as it goes against the grain of a guy who buys assembly lube by the gallon....

splatt · Feb 19, 2010

There is a huge difference between puting oil on a ring assembly and putting assembly lube on them
[quote="Danno"
]Oiling the rings and lands will lead to varnish and possible ring sticking
what a load of crap

BrianK · Feb 19, 2010

I never used assembly lube on rings but I wouldn't have thought there was an issue there - is there?

After some more thought, I went with .010 for the top compression rings, and .011 for the second compression rings and the oil scrapers. If it doesn't blow up, it oughta work well.... :!: :?: :!:

Cylinders are back on, just gotta do the head and then reassemble all the take-off parts. May get to start it tomorrow or Sunday. Wish me luck.

RoadScholar · Feb 19, 2010

Leo Geoff did the boring on my Mk III barrel; just before assembly I checked all the clearances and found that all my rings were gapped at .016, which, according to the Norton Shop manual, re-printed, is on the loose side, yet done by an acknowledged ledgend/expert. Leo also did over my cylinder head and the motor never had any visible emmissions, even when I take a sample off the inside of the peashooters all I get is a very faint bit of soot, same as from my fuel injected Ducati.

RS

BrianK · Feb 19, 2010

Thanks Bill.

Leo probably knows you're a super-aggressive rider and so allowed a bit of margin. Me, I'm a toodler, so I figured I could get away with the minimum per the revised specs, specially since the "worn" rings I took out weren't gapped much larger.

Time will tell. Here's hoping!

Managed to get the barrels back on single-handed (using the pistons in the bores first method) -let's see what happens with the head! You may yet hear a cry of "help me, Mr. Wizard...!" emanating from the Needham area....

Danno · Feb 19, 2010

splatt said:
Where did you get the larger figures from, 0.019'', from your initial measurement the rings you are replacing don't sound very worn.
0.012'' is good,the thin steel scrapers can easily have around 0.040'' at times, so if you can get 0.015'' would be ok, any reason why the new rings have no gap?thats usually a good sign just to check they are actually correct.
But your biggest question will be......... are you going to put oil on them when you assemble them ,or not.................... that will keep you awake at night now won't it.

Dry assembly is common prtactice throughout the motor trades. No lost sleep when you actually know what you'e talking about or consult someone who does.

BrianK · Feb 19, 2010

Dry it is and will be. Perhaps a little too dry. I lost track of things and forgot to put a spot of oil on the skirts. Hope that doesn't cause problems.

bpatton · Feb 19, 2010

Brian, Did you get a light hone put on the cylinders? It's entirely possible that you are fine with gaps around 10 thou. I've installed compression rings on a dry piston into a dry cylinder and pushed them through a few dozen cycles and got 5 thou in endgap. I'm told that Ron Wood had a bottom end hooked up to an electric motor where he would break-in rings. He might have even thrown in some of the legendary BonAmi

Then he gapped them.

Danno · Feb 19, 2010

bpatton said:
Brian, Did you get a light hone put on the cylinders? It's entirely possible that you are fine with gaps around 10 thou. I've installed compression rings on a dry piston into a dry cylinder and pushed them through a few dozen cycles and gotten 5 thou in endgap. I'm told that Ron Wood had a bottom end hooked up to an electric motor where he would break-in rings. He might have even thrown in some of the legendary BonAmi Then he gapped them.

In "On Any Sunday", Mert Lawill put a mix of light oil and valve-grinding paste into a newly-built motor and ran it for thousands of revolutions with an electric drill motor to lap everything together. Of course, there was no load, no combustion heat or by-products, and he would completely disassemble and clean every part before reassembling the motor to run for real.

splatt · Feb 19, 2010

Danno said:
Dry assembly is common prtactice throughout the motor trades. No lost sleep when you actually know what you'e talking about or consult someone who does.[/quote

and I reckon you should

Danno · Feb 20, 2010

If I need your advice, I'll be sure to see a psychiatrist first to figure out what's wrong. If you have an opinion on this subject, why don't you just post it instead of following me around like a chihuahua knawing at my ankle?

Ideal ring gaps?

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