Britbike forum Forums British motorcycles in general The triple forum Ring gaps

I'm sure that this topic has been done to death, but here goes.
AP Apex iron rings, +30 bore. Calculating from the data sheet gives a minimum gap of .0.0086". WSM says 9 to 13 thou.
Every compression ring I checked is right at 10 thou. I'm thinking open the gap to 12 on the second rings.
What say you?

25 views and no replies, I guess I'm good with the plan.

Not many of us have real Triple experience (I haven’t!). Even fewer will have experimented with ring gaps on their Triples.

Enlarged 2nd ring gaps, among other tricks recommended by John Healy and the late Pete Russell, may have contributed to the good ring sealing on my 650 Twin. Trouble is, Triples appear to have different ring requirements from Twins.

Triplesonline?

Works on V8 s , supposed to stop ring flutter , so better seal , and you in spec .

The only thing you need to know about ring gaps is "larger is better than smaller", so err on the larger side of any calculated measurement and you will be fine.
Think about it, you calculate 0.0086", but 10 thou would work just as well...like how much compression would you loose through 0.0014" Plus you have a second ring which is theoretically clocked at 120 degrees from this one anyway. So the answer is nil.

I agree with trrident150v. I worry more about too tight than too loose. I'd set them both at 12 thou.

My first job after graduating was at the AE Group Research and Development Center in Rugby, UK.
AE = Associated Engineering--the group included Hepolite pistons, Wellworthy pistons and rings, Glacier Metal Bearings, Coventry Radiator, AE Turbine Components etc etc.
About 200 people worked there and it was a fascinating place to work.
I worked on heat exchanger projects but shared an office with another development engineer who worked on pistons and piston rings.
One of his projects was to understand the significance of piston ring gaps.
And of course we talked.
His team ran a single cylinder air cooled research engine instrumented for power , blow by etc etc.
They ran it with different piston rings with different gaps. starting at the recommended gap for that size piston.
Smaller gaps were not investigated as this would result in the ring ends meeting.
The gaps were increased to 1/16" as per the program.
No discernible difference was found in terms either of power or blow by.
They were so surprised by this result that they increased the gap to 1/8".
Still no difference!
The hypothesis to explain it was that normally we think of the rings on the piston in a static situation--- as when we are assembling the engine.
However when working in anger the piston and rings are moving fast and reversing direction at anything around 100 times a SECOND (equivalent to 6000 rpm).so there is not much time for blowby to happen particularly when bearing in mind the tortuous passage through the ring gaps of three rings with staggered gaps.
Now I am not suggesting that you set the ring gaps to 1/8".
However as long as the gaps are above the minimum then a few extra thou is not going to make a difference in engine performance.
HTH

I've seen a rule of thumb as .004 for every inch of bore size for cast iron rings in these old air cooled engines. On a Trident with +30 over bore this works out to .0011. Like I said earlier I have always used .0012

That sounds about right. The paper which came with the pistons/rings says 0.005" per inch of bore for air-cooled racing engines and 0.003" per inch for all others.
These are AE pistons/rings, but the Covmo brand.
Still 2.67" x 0.004" gives a gap of 10.68 thou. I guess I'll file to 11 and 13. You also need heat transfer from the rings to cylinder.

...and what about the theory that the second ring would be with 30% more gap?

This is a key point because tight end gaps can cause all sorts of serious problems. Over the years I have seen from tight end gaps:

Crowns torn off of pistons.

Pin ripped from the small end of the rod.

Deep cylinder scoring from the top of ring travel on down.

Could be what happened here? I always assumed that a circlip came loose, but it was in place when I removed the cylinders. I don't know what work PO had done, but the shop where the seller got the bike does Harleys.
0.030 boring got rid of it.
New rings are now gapped at 11-12 thou top and 13 thou second.

Maybe a combination of tight ring and 4 corner seizing where the ring ends caught first.

Looks like damage from a circlip or a pin with no circlip, that the repair man has ignored.