Help needed -cylinder bore problems

[pete ardron]

I've nearly finished restoring a 1923 New Imp powered by a JAP V Twin. One cylinder is perfect but the other has a damaged bore. I've tried everywhere I can think of to find an oversized piston so that I can give it a rebore but none exist anywhere. I've tried also to find non-JAP pistons that would fit but I've drawn a blank there too.  I've been told by a company specialising in JAP's that the casting in the cylinder isn't strong enough to have a lining fitted.
 So... what are my alternatives? I guess I could have an oversized piston made, or I could have the bore ground out and then hard-chromed back to size. Has anyone out there overcome similar problems? All suggestions welcome.
Pete

[R]

What JAP engine is this - a KT/U ?.  Blind bore, presumeably ?
What size is your existing piston, and is it iron or alloy ?
It has an oil ring, or no ?
And what size are the bores at present ?
Got a pic of your piston ?

A moments reflection reveals that if the bad bore was sleeved as is, with a light cleanup, back to possibly slightly undersize if the sleeve was going to be too thin, then it is no weaker than it presently is. A few cc's here or there make no difference, if you can make a piston fit it..

Don't know about hardchrome or ceramic bores enough to answer that, leave that for someone else. Tricky in blind bores ?

Have heard of bedford truck pistons being used, out of the packet. May have to adjust the gudgeon pin size.  Briggs&Stratton make a range of engines, some pistons of which are quite close, ditto. And several firms can make any size of piston required, from a pattern or even just dimensions. Alloy though, not the unseizable iron pistons.  Cheers.

[pete ardron]

Thanks for your speedy reply. It's a 1923 KT series, so a sidevalve with a blind bore. It's on standard sized iron pistons with three (I think) rings above the gudgeon pin and one in the skirt. The piston is absolutely perfect, with not a mark on it. I'd heard that Bedford pistons would fit but the vintage piston co says that they will fit the post 1926 models, not these earlier ones.
Pete

[chaterlea25]

Hi Pete,
How badly damaged is the bore?
Any chance of a couple of pics?
I have heard of "tram tracks" caused by gudgeon pin caps worn away or taper pins coming loose
(make sure there are holes in the caps)
The tracks were sucessfully filled with Silver solder 
I havnt tried this myself but have had excellent results with cast fin repairs using sllver solder

Moss engineering in Ledbury fitted a very thin sleeve to my brothers 1910 Triumph, its pegged at the base flange, This has been running great for several years, plenty miles on it 

I have a friend who has a model H Triumph, this has been running away happily with tramtracks in the bore for years (its now awaiting its turn for rebuild with a newly aquired cylinder)

I have also heard of the bedford pistons being used, I havnt heard that they wont do in pre24 engines tho??
I know someone who has them lined up to fit to a 1920 engine, (one of his many projects???)

Cheers
John

[pete ardron]

I  can't send any pics because I put it all back together in the hope that I'd get away with it! As far as we can tell the bike was taken off the road in 1928 and hasn't been used since. The rear piston had seized in the bore just below TDC. The bore became corroded but the piston remained incredibly pristine. There are no tramlines - just a pitted area over an area of the bore. The result is that a nice compression starts to build up until the piston reaches the damaged area - at which point virtually all compression is lost, just when it's needed most. The engine will run but it runs more like a badly out of balance single than a V twin. I'll give Moss engineering a ring tomorrow - thanks for mentioning them, It was Cameron Racing who told me that JAP sidevalves could not have liners fitted but since then several people in both the New Imperial Association and in the VMCC have told me that their advice isn't always either unbiased or of the best!
Many thanks,
Pete

[pete ardron]

A big thanks for all the advice I've received. Moss Engineering say they've relined these bores in the past and metal thickness isn't a problem. So the barrel is currently winging its way to them for restoration.
Peter

[chaterlea25]

Hi Peter,
Good to hear a solution has been found
Let us know how you get on when you have the bike running
Glad I could help, and its nice to get some feed back

Best Regards
John