Where do I go, where do I go, where do I go now?

[spookefoote1956]

I've ordered some new gaskets and looking at a rebore, primarily to remove the scoring, but also to fit new rings with the correct gap 0.006". The engine's in bits now so it would be daft not to address the scoring. I'm not happy with the JP but it's not like there's a multitude of options. Perhaps use a different brand of rings?

[Greybeard]

If youre having it rebored, you'll not be able to reuse the old piston (unless Ive misunderstood what youve said, in which case my apologies) A new piston should come with appropriate rings and more often than not will be gapped properly. I wouldnt get too hung up on the gap size unless theyre too small of course. An oversized gap will have very little effect on this type of engine in my experience.
I have JP pistons in both my B31 and Ariel NH and theyve been fine. I think most problems arise when engineers with no experience of air cooled barrels bore to tighter water cooled clearances - and that can affect pretty well any make.
Is there an oversize marking or dimension stamped on the piston you have?

Steve

[SPRIDDLER]

I wouldnt get too hung up on the gap size unless theyre too small of course. An oversized gap will have very little effect on this type of engine in my experience.
I have JP pistons in both my B31 and Ariel NH and theyve been fine. I think most problems arise when engineers with no experience of air cooled barrels bore to tighter water cooled clearances - and that can affect pretty well any make.

My thoughts entirely.
These long stroke low compression single engines are pretty agricultural and will run happily with relatively oversized ring gaps.
I fitted a JP piston to my G3LS which ran fine as my daily and camping rally transport, covering around 25,000 miles in the 5 years before I had to unwillingly put it into hibernation in the shed.
For the rebore I used the clearance rule of thumb of 1.5 thou inches per inch of cylinder bore plus half a thou. It didn't seize nor have any piston slap.

[dave16mct]

If it was me I'd clean that piston up. Hone the bore and see how it goes. Won't cost you much if anything. Worth a try.
Dave.

[spookefoote1956]

Morning everyone . My engine is a 56 which apparently was a change over year for pistons. As a point of interest what are the differences between the design of that piston and the previous one?
Cheers, Chris

[dave16mct]

If you look at the '55 parts list and manual (hint No1 ) you'll find 1955 18S 6.3:1 pt no 016858. Looking at the 1956 parts list and manual (hint no 2!! ) you'll find 1956 18S 7.3:1 part np 018927. So it's the domed 1956 piston which is higher ratio than the '55 flat topped one. (Only guessing!) I think the '56 exhaust cam was slightly different as well.
See you at Farmyard Ales tonight.
Cheers Dave.

[spookefoote1956]

I thought it was just compression. Cheers Dave. I think it's going to be wet tonight.

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[spookefoote1956]

Morning everyone. Can anyone tell me where I can source some unused +20 hepolite rings for a 1956 piston please.

I've seen these on fleabite https://www.ebay.co.uk/itm/153544385879 but 86mm seems a bit big for +20

Cheers, Chris

[Greybeard]

https://www.coxandturner.co.uk/

Very helpful and quick service. They found me a set for my '26 AJS 500 and supplied within a couple of days. Don't risk getting the next oversize and hoping they'd 'do' - they won't seal properly and the engine will smoke like an old mill chimney. Ask me how I know Though in my defence the rings were wrongly boxed NOS for a 16MS.

Steve

[dave16mct]

Funny you should say that as some people recommend getting the next oversize and filing the gap to suit (saying the gap is often too big with exactly the correct ring size). I did that years ago when I couldn't get the correct size (+20, so I fitted +30) and had no problems.
Dave.