Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Will Tri Unit 500 fit easily into B25/44 frame?

Hello All,
Sometime this summer I will be taking possesion of a cashe of Tri/BSA Unit Single stuff that I swapped some other goodies for. Anyway, I will be suddenly rich in T25 frames and I'm going to convert one to a hardtail and build a small bobber for fun. My question is, has anyone had experience fitting a Triumph unit 500 engine into one of these frames (1968-70 version)? I recall seeing a very small picture in a classified ad of this arrangement but have no idea what had to be done to accomplish it. I'm looking ahead to the future a wee bit in my usual fashion but may try to up-motor this machine one day. Thanks

I've considered doing something like that myself. I also have some T25/B25 frames laying around.
A guy I know who used to work for Eric Cheny, and later for Bud Ekins (he's got his share of "special" building experience) says it shouldn't be a difficult conversion.
The trickiest part of the job would be getting the sprockets on the frame and engine to line up.

Actually, the trickiest part of fitting a Triumph 500 motor into a B25/B50(alright, or a T25) frame is getting the motor to sit low enough in the frame so that it doesn't look silly. If you get a good look at a TR5T Trophy Trail/Adventurer frame, you'll notice that the bottom rails are quite a bit wider than the unit single variety; the front motor mount is also higher. The engine also needs to be moved to one side (can't remember which) to line up the sprockets.

It can be done: I've seen conversions done with both B25/B50 and B44 frames.

Cheers,

Costa

Two reasons not to do it:

1) The TR5T frame is almost the same as the B50 frame, but was widened at the factory to fit the 500cc Triumph engine. (no cutting needed).

2) It is my understanding that even if you can get the engine into the B25/TR25 frame it will shake it to bits once you run it for a while.

Stick to the TR5T frame for the 500 engine, or better yet, buy a Rickman kit for it!!!

LTR

If a 441 doesn't shake it to bits, I don't think a triumph 500 will.

Hello all

I am aware this thread is really old - but I did exactly this in approx 1989, this picture is from when it was first used on the road - it wasn't quite finished..

It fitted without too many frame mods, I sold it due to lack of funds and space to keep it.

I am in the UK so it is unlikely to be anywhere else but I would really like it back

Looks like a VERY nice job! (except maybe that oil filter)

Any more pix?

unit 500 single? (Tr version of the B50)... that fits in the dry frames pretty easy with some adapter plates. did it a couple times long ago and as I remember it was the rear mount that was different. if you mean the twin... I don't know

The filter does look exposed, but it is quite tucked away, the B25/T25 oil in frame bikes had quite good ground clearance.

It's been a long time but I am pretty sure the oil filter used to be in the front downtube - this was one of the areas that needed modification to give enough clearance for the engine.

I have a dozen or so pictures of various points in the construction - I could post them if it would be of interest ?

This frame is from the 250 oil in frame singles - the B25 or T25, the front brake puts it as the T25SS (in the UK, not sure if they got to the US). I rode the bike when it had the 250 engine and it was surprisingly good - virtually no vibration through the footrests at all, then the bloke who owned it crashed it, bent the forks, dented the tank, and finally sold the engine !

I bought it as a rolling chassis that needed an engine, which I happened to have just kicking around.....

The frame is much tighter around the engine than a B50 type, there was no way the unit twin would fit directly, I am trying to remember but possibly the rear mount was in the right place to start with - which would suggest the distance from the centre line to sprocket was the same, this makes sense as the gearbox internals/clutch would be similar.

Frame drawing, cover the Unit OIF 250 and 500 engines as the mounting points are common. Pre OIF 250,350,441 engines have a narrower rear engine mount.

The thread title is deceiving IMO.

More pictures have arrived - it took me a while to get them scanned from the original photographs, they just show stages in the build process.

This group are of the process of fitting the engine to the frame and deciding what mods were needed.

This second batch were taken some time later (in 1987) after the engine brackets were made, the oil tank modified and fitted, and nothing done to the tank as I was looking around for a better looking one.

The final batch are when it was finished enough to be ridden, hope they are of some interest.

Why in the world did you sell this? I certainly understand why you would want it back!

Were you able to ride it much? Have you ever ridden a TR5T for comparison?

Man, I do like this bike... it kinda says "find me a desert and flog me" (sorry!).

I had to sell it for a couple of reasons, one was lack of money (as usual !), the second was I had started a new job that was going to take me all around the UK, finally it was in a rented garage.

I used to ride it to work - it really used to annoy the stuffy types in govt dept I worked in (which is/was good !) - the main reason it annoyed them was just how loud it was :D, I have ridden many Triumph twins (not a TR5T) without silencers and they had nothing on this - no idea why !

Glad you like it - as you should - Triumph themselves did something similar I believe (but mine was better - all the engine mounts were S/Steel).

Looking back it makes no sense....

Why did you have to use an external oil tank (Sorry if you already mentioned)

Several reasons, firstly the OIF capacity is quite low IIRC, I wanted to fit a proper oil filter, also wanted to fit an oil separator - this is the lump on the top of the A50 oil tank.

But, the most practical reason was because I had to cut the front frame tube a bit to get the engine to sit right in the frame, I hope I am remembering correctly that this was where the drain plug was.

Do they have deserts in Oregon ?

That's where it is now :0)

Edit: This post makes more sense if you read this thread

https://www.britbike.com/forums/ubbthreads.php/topics/905247/re-trying-to-locate#Post905247

24,000 square miles of it... I'll bet that bike is having fun!

Good job on locating it, but doesn't sound like it's coming home.

Wonder what it looks like today...?

Well, he says it now black, hopefully he will post a pic or two, I think the band are touring right now so he could be a bit busy.

It would cost a bit to ship it home, but as he's had it over 30 years he might want to keep it !

yes ,
it is considerably drier on the eastern side
of Oregon's Cascade Mt. range . and Geographicaly ,
the neighboring state to the south ... of Eastern Oregon , is Nevada .