Fitting Webley MKII Service Rifle piston rings

[plumbgun]

Hi all, I am doing some research on the Webley MKII Service Rifle, in my own small way, and will publish anything I find that is thought to be accurate and useful. Have just replaced a piston ring (one from Chambers) and wonder if there is a technique to doing this. Do you, for exanple just put the ring into the groove, or do you open up the ring a bit first, so that it has to be gently compressed before putting into the rifle? The ring I ordered was closed tight, but the (worn?) one that I took off was sprung so it opened up on removal. Which, if any is correct? Would be grateful to hear from people who have actually "been there" Thanks for reading.

Paul M.

[wonky donky]

The one in my MK2 Service is sprung & everything else I have replaced rings in including target rifles & pistols have been slightly sprung too.

[plumbgun]

I appreciate your comment. Let's see what more people say.

[Garvin]

I appreciate your comment. Let's see what more people say.

Paul, just so you know, what wonky donky reports will be based on many, many times the experience of your ordinary airgunner. Maybe x300? Just FYI.

[plumbgun]

Now that is what I call an endorsment!

[deejayuu]

My knowledge of piston ring sealing is limited with air guns but considerable with other applications, machinery/engines/pumps etc.
Interesting to me is the designer's view that radial spring force is useful to provide initial sealing on start up, certainly in engine applications, but side play in the grooves is more critical in running conditions.
At high speed/pressure conditions the pressure trying to pass the ring gets behind it and greatly increases the outward radial pressure to improve sealing. Spring force alone can result in the ring "floating" in the cylinder so not sealing effectively.

Many years ago Harry Ricardo the diesel engine guru was involved in a tussle with noted engine manufacturer regarding severe "blow by" in new tank engines causing excess crankcase compression and power loss etc.
After much heated debate he demonstrated by running the engines with the sump pan removed. One with manufacturer's tolerances the other with increased side play to allow for expansion etc
The flaming results spoke for themselves. There were photo's as I remember may even have been filmed. After all he produced film of the flame spread inside a combustion chamber so should have been a dawdle.

Sorry for the ramble but was reliving the past, again!

[plumbgun]

You are clearly a very knowledgeable person, and I thank you for your comments. I wonder if you think the rings would give a more reliable seal if they were opened ever so slightly so that they had to be manually closed just on inserting into the compession chamber. Does your experience allow you to help me here?

Thanks,

Paul M.

[Fronteria]

Hi. Paul
Have you tried the ring in the bore?
If not I suggest you do, as if it has no ring gap and the cylinder has a slight taper due to wear it will either jam the piston or break the ring we are only talking a couple of thou. ring gap at the smallest point of the bore that the ring passes through during during the stroke of the piston.
A mate of mine replaced the rings on a Webley MK11 Target pistol and got the piston jammed at the end of it's stroke because the bore had worn tapered by about three thou. the rings had no gap and the spring jammed the piston and rings down into the tapered bore, in trying to get the piston back out he used the barrel and cocking linkage and bent the barrel in doing so.

[deejayuu]

Good advice from Fronteria. The ring gap is also critical when temperature variation is a factor so not a problem with single action spread over time but repeated cycles in short time produce a big change in temperature at breech end of the cylinder. Try using a bike pump to inflate a tyre and you notice the pump body gets very hot at the outlet end. That's compression at work not friction 'cos that would heat all along the body. Remmber to check the ring gap when square in the bore. So push the ring gently with the bare piston or close fitting socket on an extension. Check at several points along the bore
To answer your original question it's my opinion that the ring should be slightly larger than the bore so sprung in to place on assembling. This will ensure good contact with the bore in use.
The Mkll has variations, one ring, two narrow rings, leather washer, even leather washer and ring have been seen.
A drop of light oil on the ring/groove. If it's two rings set the gaps 180 degrees apart.
Good luck.

[plumbgun]

Points well made, and taken. I had not thought about the thermal effect (surprisingly) and the irregular bore issue is important too. I see a small gap in the ring is essential now. My new (Chambers) ring when slightly opened (amout 1/16") went in well, and I am delighted at how powerful the weapon has become, for comparatively easy cocking effort. The phrase "Shoots like blazes" comes to mind when pellets are utterly destroyed against a steel target!! I really appreciate the comments, and will keep experimenting.

Paul M.

[deejayuu]

Don't quote me but I have read somewhere that the Mkll cylinder was built to stand some dieseling sdue to the compression ring needing some frequent lubrication at that time since obviously the modern products where not available Must service the Services soon

[Phil Russell]

This may or may not help..... a few years ago I serviced/rebuilt a couple of MkIIs with rings. I assembled them with 'modern' lubricants. Performance was pretty poor. I then cleaned them out and relubed with car engine oil as piston ring lubricant. Normal service was resumed ... and there was no visible or audible violent dieseling or excessive smoking. Now I cannot claim there was no dieseling at all, just that performance was better with what I believe was the recommended lubricant at the time they were made.
Cheers, Phil

[plumbgun]

Hi Phil - Interesting,which "modern lubricant" did you use btw?