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Discussion Starter · #1 ·
Hi Folks-
I'm about 1/2 way through a project-a '72 BSA Thunderbolt. WAIT! -------Before you flame me for BSA spam-------- I've had 2-72 Bonnies in my time, and was wondering the difference between the frames?? Looks as though the rear engine mounts and head steadies are the only different pieces to interchange the engines. Am I all wet here? If this Beezer motor goes south on me I might want to bolt a 650 Triumph engine into the frame rather than going through the Beezer mill. I've got an extra 71 Triumph tank and seat and a head steady, you see... Just tossing thoughts around..
Any thoughts from the gurus would be appreciated.
(Humm, if it would work, would it be a Beezumph, a TRISA or a Bastumph????) :-D

Thanks-
Mike
Kansas, America
50 MPH sustained wind tomorrow---I'm driving the pickup!
 

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The only first-hand advice i can give you is to try it and see if it fits, I've never tried it.

However, I have a BSA OI frame, and a set of blown Triumph cases, so I could attempt a test-fit. Only problem is I'm headed to California tommorrow and won't be back in till the day before the turkey hits the table.
 

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It would be a TriBSA. You are not the first to put a Bonnie eng.into
a BSA frame. The Ton Up boys did it all the time. :chug:
 

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Discussion Starter · #4 ·
Hi Folks-
Thanks for the replies. This isn't a pressing issue, the old T-Bolt engine does run pretty well so far, just looking at a "plan b". Never know when you'll shell the bottom of a BSA, you know. Had a perfectly good(?) 67 Hornet a decade or so ago that got to playing the hammer symphony for me. Had a crank key shear on a 441 Shooting Star at about the same time in history, my first 5 mile push home. Strike 2 for Small Heath! Been wary of the Beezers since, but I'm a sucker for a Brit bike sitting forlornly outside of a Harley guy's shed.

Mike
Kansas, America
"If you're gonna beat the rust, you have to think like the rust. It never stops, it never sleeps. It's like the Viet Cong----The Rust Cong."
 

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The front and bottom center stud mounting locations are also not the same as Triumph frames....in other words, it would be easier to get some BSA cases and parts than to put a Triumph engine in a BSA frame.
 

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Discussion Starter · #7 ·
Hi folks-
Thanks for the replies----

Rats! So much for "Plan B" Better treat the old Beezer really nice!

Mike
Kansas, America
 

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Or take an OIF Triumph frame, common item and not spendy, and attach all the running gear. Then get an engine, also pretty common.
 

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I never noticed that. My A10 weighed 450 pounds, My '69 A65L weighed 415 pounds, my Triumph (after some modifications), was 350 pounds. The A65s don't run long enough to find out which is faster. The A65s have shorter stroke and bigger bore, which should argue for more top end power, but the weak rods, iffy oil feed to the crank, and poor head flow limited THAT. BSA did make one that came close...the 72 750....which was a stroked 650, with a better oil pump rods. And that made it almost identical to the Triumph T140.
 

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BSA's are faster than Triumphs.
doing the british thing, my 71 lightning has more go than my 72 tiger.2 carbys lots of interchange parts, I would rebuild the beeza rather than try and fit a trumpy motor in the lightning frame.Both are oif but different engine mounts, different seat mounts, taco and speedo are on different sides.Save yourself a headache and keep them seperate. A very interesting part of history the early seventys for british bike entusiasts. I think about same throwing a bottom end ouch!! I try not to punish the old girls nowadays, always keep an eye on my oil and change it every 500 miles.Oil is a cheap commodity versus engine parts ha ha. well good luck..
 
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