Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Unit 500 parts interchangeability

Hi there.

I'm embarking on a project to build a Greeves - Triumph (Grumph). I have the donor Greeves and a job lot of engine parts including 2 cranks, 2 crankcases, 3 cylinder blocks, 2 heads etc etc etc. One of the cylinder blocks and a head is for a 350, the others 500. Both crankcases are marked as 500s. I intend to build the engine as a 500.

My first question is: is the crankshaft for the 350 and 500 the same and if not how can I tell the difference? I will also no doubt be coming across lots of other compatibility questions and look forward to engaging in this forum.

As backround I've owned and ridden British bikes for more than 50 years and rebuilt many. But I'm new to Triumphs, having been a dedicated Norton owner for decades - and still am.

"My first question is: is the crankshaft for the 350 and 500 the same and if not how can I tell the difference? I will also no doubt be coming across lots of other compatibility questions and look forward to engaging in this forum."


Racing 350's, I can say that the 500 crank is the same

I haven't found any differences

In fact, I'm using a 500 crank in my 350

Many thanks, that makes life easier.

Also, another thing to keep in mind

Early Triumph 350 (and maybe 500) bushing cranks are different from later bushing cranks

I had a crank from a 1958 Triumph T21 and the crank was shorter in length when compared to a later bushing crank

The cheeks on the early crank is similar to an A50 / A65 design

I used a T21 crank in a set of 1963 cases and I had to shim the crank to prevent end float and to center the roads since the crank is shorter...

You can use an early bushing crank in any bushing motor crank case, however you cannot use a later bushing crank (which is longer) in a set of early cases

The chances of you having a early crank is slim, I would assume the "early" crank was used only for a few years (1957-1958 or so?)

Sorry about that!

Thanks, all helps. The parts I have are a fairly motley collection. One of the cranks is in good condition - it has the rods on it and there is no perceptible play in the big ends although I will of course remove them to check. The other has surface rust and has no rods. The threads are good and I think the rust will clean off OK. I have no idea whether they were all collected at different times or whether they started life as assemblies.

Do you have any dimensions I need to check? The crankcase I intend to use is numbered H15902 which I think dates it to 1960 - I don't know whether you would class this as "early"?

This is just some of the parts: [Linked Image]. This is where it's all going in the fullness of time: [Linked Image]

I don't have an engine # cut off

My early crank was from H3078

1960 might be a later type

Very possible it could have only been the T21 cranks / cases NOT the 3TA crank or cases

Thanks again, crossed post while I edited.

https://www.abebooks.co.uk/Triumph-...Ikp4UN5L-qsIACGVe1GOCPATfooaAno2EALw_wcB

I have this book (somewhere!)

Might be worth getting a copy
Without finding it I can’t say if it would help

Thanks, I'll have a look for that. Without delving too deeply yet I don't think the Triumph engine is particularly strange but of course there are always traps lurking for the unwary.

This is my garage with the Greeves and some of the Triumph parts:

[Linked Image]

Bear in mind that the balance factor will change when swapping cranks/top ends, though what the balance factor should be for a Grumph, goodness knows!

Different parts 350 to 500 are conrods, barrel, pistons, head. Your case should be OK. there is a lot of info here:
https://triumph-tiger-90.com/

Thanks, that site is indeed very useful - as is CBS's for manuals etc. My conrods are marked E3703/4 - which doesn't correspond to the parts book for either 500 (E4001) or 350 (E3702). Most of the good bits are for a 500 - will these conrods work in that?

As for balance factor, I can stand a bit of vibration, having once owned an Atlas.......

The number you have E3703/4 is just the bare rod (a steel stamping?) The 500's had alloy rods with steel caps (as did the later 350's), probably a better bet, though the steel rods would work.

The steel rods feature a smaller wrist pin I believe. Not sure about the later 350 alloy rods.

yes, you will need to check the piston pin diameter (wrist pin is called gudgeon pin here). 350 probably different

Yes, need to check these out. The rods are steel. I do have a 350 top end including pistons but it's not as good as the 500 bits. I've test fitted the crankshaft in the cases and there is just perceptible play on the t/s bush. I'd really prefer not to have to rebush if avoidable. The mainshaft reads a thou or so under nominal size with no scuffs or scores.

Thanks for all help!

Just measured and you're absolutely right - they're 350 rods. Fortunately I have a decent set of barrels, pistons and head to go with the. In truth perhaps a 350 is getter suited to the Greeves frame......