Should I build a TriBSA?

[Tjwood]

Hi. Like a lot of people I have a large stash of parts from various other classic bike projects - but I’ve never owned a ‘fully functioning’ BSA framed bike. So I now find myself with a conundrum: I have a really tidy 1970 A65 frame/swing arm (but no engine) and a complete 1969 Triumph TR6 unit engine (but no frame). I thought, ‘Easy, I’ll build a TriBSA by marrying up my TR6 engine with the A65 frame’. However, the TR6 engine is a bit too long to fit in the space available between the A65 frame’s front down tube and the swing arm cross-tube. I’d (foolishly) assumed that there would be plenty of room as both the A65 and TR6 engines were 650s. So now I’m not sure what (if any) Triumph engine would fit into the A65 space. I was wondering if there are other TriBSA builders or owners out there who have an late 60s A65 framed bike who could offer any advice on what ‘alternative’ engine would fit into my frame. My other option is to sell the frame or engine and either build a complete A65 or a complete TR6 (depending on whether it’s the frame or engine that I sell). The only problem with that ‘solution’ is that A65 engines out there for sale (even quite ratty ones) seem extremely expensive and TR6/T120 frames are as rare as hens teeth. Any advice gratefully accepted. Thanks very much
Tony

[John Dynostar]

well this is my project Tribsa in bits which should be been built shortly
if I get time.
I could drop the engine plates in for you to see if you like
also there is useful link here
https://classicbikepartsuk.uk/product/triumph-engine-to-bsa-frame-tribsa-conversion-plate-brackets/
not sure how relevant it is but you can read the text to help.

[Tjwood]

Hi. Thanks for your reply. I see that you are using a pre-unit engine - I think that’s where my problem lies. I can’t be sure, but I’m guessing that the pre-unit Triumph engine and gearbox require less space than a unit 650 engine. I can’t think of any other reason why I’ve never seen a TriBSA using a unit Triumph 650 in an A65 frame. Maybe a unit 500 engine is shorter - I don’t know.
Tony

[John Dynostar]

here you go 
T140 into A65
https://www.triumphrat.net/threads/tribsa-t140-rebuild-completed.863442/

google is your friend 

[Tjwood]

Hi. Thanks for the link to that T140 TriBSA. Unfortunately, the guy (don’t know his name) said that he has used an A10 frame, not an A65.

[John Dynostar]

not sure this will help then 

https://cybermotorcycle.com/gallery/bsa-frames/

[DAVE BRADY]

Hi,

Subject to clarification I would say that the 500 Triumph is slightly smaller as it is based on the 350 whereas the 650 had its own cases that then became the 750.  If you have ever seen a 500cc Triton you will how small the 500 engine looks in the Norton frame.
Why not try and swap the Triumph engine for an A65 one and keep life simple?  I would think that it is easier to find/build an engine than to find a good rolling chassis or gather bits to make one.

Dave.

[Tjwood]

Thanks Dave. Good advice - cheers. I guess it’s just a waiting game now until a decent A65 engine turns up (at a ‘sensible’ price!). Shame, I was really hoping to do the TriBSA thing, but maybe that’s going to have to be for another project further down the line.
Regards
Tony

[ferretjuggler]

A few years ago I had the misfortune to purchase a late A65 OIF type frame that some misguided individual had decided to fit a LH shift T140 engine into.
What a disgusting mess it was !
The lower engine mount is a couple of inches different between the two engines, but there was no sign of any modification there, so I assume that the bottom mounting was just ignored and left hanging there.
All put back to standard now but lots of PITA welding etc.
If you really want to build a TriBsa (and why not ?) I'd suggest using a pre unit Triumph engine in a late A10 type frame.
Just a case of engine plates and spacers etc.
I think you'd need quite deep pockets though

[Mike Farmer]

 

PM Sent

Mike

 

[Tjwood]

A few years ago I had the misfortune to purchase a late A65 OIF type frame that some misguided individual had decided to fit a LH shift T140 engine into.
What a disgusting mess it was !
The lower engine mount is a couple of inches different between the two engines, but there was no sign of any modification there, so I assume that the bottom mounting was just ignored and left hanging there.
All put back to standard now but lots of PITA welding etc.
If you really want to build a TriBsa (and why not ?) I'd suggest using a pre unit Triumph engine in a late A10 type frame.
Just a case of engine plates and spacers etc.
I think you'd need quite deep pockets though

Thanks for your thoughts and advice. I know what you mean about costs - I’ve already spent around £900 just getting the frame and forks and they’re all still in an unrestored state, so there’s plenty more financial pain to come yet. I had looked at using a pre-unit Triumph engine but the costs of getting one put me off. Interesting that you have suggested a late A10 frame. Do you know if that frame has a larger space for the engine/gearbox than a 1970 A65 frame or is the pre-unit Triumph engine and gearbox a shorter ‘lump’? I now understand the term seen in so many eBay sales listings - ‘stalled project’! Mine hasn’t even taken off yet!!
Thanks again
Regards
Tony

[ferretjuggler]

Hi Tony.
I'm no great expert on pre-unit bikes or building hybrids.
All I can suggest is that you search the images you can find for TriBsa hybrids.
I'm pretty sure that both the pre-unit Triumph power train or the large unit Triumph engine will fit comfortably in a swing arm A10 frame.
Back in the day various tuning specialists had a profitable line in selling conversion engine and gearbox plates to people wanting to build specials, usually Tritons.
You can still track them down if you have enough patience.
Now for the bit that will probably upset folk !
Having a great pile of parts for a certain unspeakable Japanese twin (Yamaha XS650), I've tried fitting the XS engine in a selection of British frames, just for the hell of it.
The XS lump is deceptively large, Yamaha did a brilliant job of hiding it's bulk by clever arrangement of the cycle parts and exhaust.
Only when you try to shoehorn it into another twins frame does the size become apparent.
The only British frames that I've ever seen one in are BSA A10, and Norton Featherbed.
Just be aware that a unit Triumph engine fitted in either of the above will probably look a bit lost, with a big gap in front and behind the power unit.
I hope that this is of some help

[Tjwood]

That’s really useful information - thanks for sharing it. I made the classic mistake of looking at the engine and looking at the frame and thinking, “ Yeah, they’ll fit, no problem”. I’m amazed that the A10 is so much larger - maybe I’ll just drop the TriBSA plan and just look for an A65 engine to rebuild.
Regards
Tony

[chaz]

ahh the XS650 engine... hens teeth. rocking horse droppings etc.
I bought a Wasp scrambles sidecar rolling chassis, with the intention of rebuilding for my boys to race.
The sting was, I couldnt get an engine! Seems like those classic boys will buy any XS650 motor they can get their hands on.
As far as I know they are still running today, there was a guy in the midlands Puma, was going to build the best motor he could as he had hear tales also there was a Southern builder also using them but I think he died.

as an option, we were told to try a Honda Dominator NX650 motor as easier to get. Also on the XS saga, I had to service a XS500 last year, only made them for 3 years, no oem oil or air filters (and probably most other parts) left available. The oil filter I found in Holland and cost €80. didnt fit , but only if I took generator cover off, no gaskets..