Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board 5T .080" pistons?

I have a set of damaged 5T barrels on +.060". A friend needs early barrels but they're getting hard to find these days. Are +.080" pistons to be found anywhere? A search reveals that +.060" are available through several vendors but so far none bigger. 65mm pistons from another engine may be the answer, if the other dimensions are reasonably close. I've looked at C25 pistons but at 67mm I think that may be a step too far for reliability.

SR

Another option to consider would be having the barrels re sleeved.

Absolutely, we might do that, but sleeves are £60-70 a piece and fitting them is costly as it requires two boring operations, as the sleeves need boring or at least honing to final size. We have pistons though, which helps.
Simply boring it out to 65mm would be cheaper, always a concern... And I think the barrels could take it.

SR

I read recently about someone using nicasil on a cast iron barrel. I have only ever used it on a Gilardoni alloy barre, but they were able to put on quite a lot! I used Langcourt in the UK.

I've had plus 80 pistons go through my hands. They were the Daytona type. I've heard/read of 500 Triumphs in hillclimb competition that are at 540 cc. don't know what size pistons one would need to get to 540cc but......

Cheers, Wilf

Just to clarify, I think Stein is talking of pre-unit 5T barrels (standard bore 63mm).

Folk often confuse pre-unit 500's with unit 500's. They are entirely different (whereas the 650's are largely similar).

The unit 500 has a wider bore (69mm) so the Daytona pistons won't do for Stein.

Oops.....my mistake. Gordo emailed and the plus 80 pistons were squish band pistons.

Cheers, Wilf

Now that's interesting! Something to consider for other projects I think. However, my barrels are damaged by a gudgeon pin adrift and the score is so deep I doubt plating would do.
A friend called last night and said he'd found a pair of liners in his stash (in his case it rhymes with trash for a reason) that he thought might fit. He hasn't named a price yet but he knows their worth and needs money, so I'm still looking for suitable pistons...

SR

I guess this is a pre1956 engine, the '56 on can use 650 barrels. I would contact Langcourt just to see what can be done (I'm curious myself), they do deposit quite a lot, dont really know the process.

The Nikasil platers here will weld up gouges and machine first before plating

I seem to recall Hughie Hancox saying over boring the 5t and 6t barrels beyond what the factory recommended, was a bad idea, the barrels got very hot or something similar.

Sadly there aren't a lot of pre unit 500 cylinders that aren't at least .060" by now! They haven't made the 5T small base cylinders in 66 years! Anyway my friend recently sleeved one of these and put photos of the process on his instagram.
https://www.instagram.com/p/CWkRIyULRGT/
Anyway I'm sure the work was not cheap but if you are actually going to ride it you may want to look into sleeving. Robbins pistons made some .080" and .100" high compression 63mm pistons though if you are looking for high domes. There may be some floating around. If not check out Leif's instagram to see what is involved in the sleeving and bringing a cylinder back from the dead!

With the transport costs, taxes and fees incurred, I don't think it's a viable option for us, a set of liners would probably be more cost effective. Besides, Nikasil requires rings to suit, so I doubt this is the way to go for a humble 5T.

The story is this, a friend's youngest (20) is restoring a 54 Speed Twin, but it came with later cylinder barrels. They had been crudely adapted by grinding out the outer stud holes, which will sort of work. It's an eye sore though, and he would like to have them changed out for proper small base ones. Now I've just got hold of two, one with internal drains. Both are scored by a gudgeon pin adrift. One set is on +60 and the other on +40, but the latter is sleeved already and can't take a +60 rebore.
The funny thing is, or sad thing perhaps, is that I'm currently working on a 57 Speed Twin that came with small base barrels. The sad part is the outer stud holes. You can imagine the bodgery they'd been subjected to to make them fit the big base! The owner had the correct barrels on the shelf, but the butchered ones were on nice +20 bores. I wonder if the flange could be welded up and drilled?

They really made those old Speed Twins earn their keep, didn't they.

SR

There's that, reliability may suffer. I do think +80 might work though, the barrels are quite substantial. I wouldn't race them for sure, but for the gentle use it's going to see, I think it may just work. I don't think they were meant to take more than +30 back in the day, but new barrrels were available then, at a reasonable cost even.
Fitting liners isn't always safe either, there's little structural integrity left in the barrels, "a stack of big washers" as they say. Sleeved barrels have been known to crack near the flange, where they are thinnest. The sleeves in one of my small base barrels are 67mm in OD which means a +.160" over bore.

SR

Leif does nice work for sure. Leif is a proper Viking name by the way, very common here. I have a friend who can fit them for me, and sleeves are available, so we will probably go that route, if +.080" low comp pistons can't be found.
I've been looking at 67mm B25 pistons but that would probably be stretching it, as it's about the same size as a liner.

SR

Hello SR,
I need to have a look at my stash of bits, I have a post '56 set of barrels @ + 60 but good bores, all stove enamelled, but it may be part of a complete engine (in bits), I need to check. I have been using late crankcases in 750 engines, I think I tried to keep this as a complete engine, but can't be sure. I'll look again at what I have, but that'll be tomorrow. Have you checked the piston list on F W Thornton ?
Mick.

Hi Mick,
Thanks, but pre-56 is what I'm looking for... that's possibly what you meant?
A friend says he's got liners for me, will check them out and see how much he wants for them. It all depends on how much my customer/friend wants the barrels in the end.
If it was my bike I'd stick an iron T110 top end (which I have) on it, but then I was never very keen on slow bikes...

SR

If that was true, the all alloy pre-unit T100 and the GP couldn’t been successful in use and even racing, but they were
40bhp or more is quite common on them…(if proper set-up)

Ofcourse when removed too much cast iron it can be true… , bit the alloy ones aren’t very thick either, just had my alloy T100 re limered ;-)