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Posted By: 70BSABobby M21 in a B Frame - 06/12/19 11:40 pm
Hey guys, I'm torn on whether or not I should pull the trigger on purchasing this bike as my next project. It's a bit odd, it's a 1952 M-21 engine in a 1952 or 53 B series plunger frame. I'll just list the good and bad (that I know) and see what you guys think.

The good

1. All new paint
2. New wheels
3. New headlamp
4. New mag
5. Rebuilt carb
6. New tires
7. All parts are there except for speedo and exhaust/silencer.

The bad

1. Owner has never had it running (owner never tried to get it running though)
2. Mismatched engine and frame
3. Needs a title.

The owner is firm at $2,600 USD. If this was a matching frame/engine it would be a no brainer. The other thing that bothers me is it's a weaker engine from a different series in a frame that had a more powerful engine. I'm about ready to just do it, have him title it as a 1952 B33 as he still needs to title it (I won't buy until I see one) and either ride it as is or try and source a B33 engine.

What do you guys think, is this a good deal or should I pass? These bikes are extremely rare in the states as far as I can tell so I'm worried I won't find a more original bike for close to this price.

Thanks in advance for any advice/feedback!





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Posted By: Don P. Re: M21 in a B Frame - 06/13/19 1:13 am
https://www.ebay.com/itm/1949-BSA-B34/254257096536 Take a look at this one.At least it runs and has a title
Posted By: BSA_WM20 Re: M21 in a B Frame - 06/13/19 8:45 am
The B frame is a LIGHTWEIGHT version of the M frame so there is no problems frame wise other than the tabs for muffler & exhaust will not line up.
Posted By: Ginge Re: M21 in a B Frame - 06/13/19 10:46 am
It’ll never break any speed records but it’ll be simple to work on, easy to find parts for and it’s a ‘50’s BSA.

Pull the trigger on it when you see a title.
Posted By: 70BSABobby Re: M21 in a B Frame - 06/13/19 9:16 pm
Originally Posted by BSA_WM20
The B frame is a LIGHTWEIGHT version of the M frame so there is no problems frame wise other than the tabs for muffler & exhaust will not line up.


How would I remedy the exhaust not lining up? Would I buy a different part or would I need to do some cutting/fabricating? Thanks!
Posted By: Andy Higham Re: M21 in a B Frame - 06/14/19 9:34 am
If you are asking questions like that maybe a special is not for you
Posted By: Ginge Re: M21 in a B Frame - 06/14/19 10:49 am
Quote
How would I remedy the exhaust not lining up? Would I buy a different part or would I need to do some cutting/fabricating? Thanks!


Well, you could cut the frame tabs off and shift them, or you could cut the exhaust tabs off and shift them. Both would require a mock up with the original parts.

You could leave everything standard and build a custom exhaust.

If you’re lucky and the tabs aren’t too far off each other you could fabricate spacers or linking brackets.

Nothing difficult. Just might need to have it all there in the flesh to measure and nut out.
Posted By: 70BSABobby Re: M21 in a B Frame - 06/14/19 11:23 am
Originally Posted by Ginge
Quote
How would I remedy the exhaust not lining up? Would I buy a different part or would I need to do some cutting/fabricating? Thanks!


Well, you could cut the frame tabs off and shift them, or you could cut the exhaust tabs off and shift them. Both would require a mock up with the original parts.

You could leave everything standard and build a custom exhaust.

If you’re lucky and the tabs aren’t too far off each other you could fabricate spacers or linking brackets.

Nothing difficult. Just might need to have it all there in the flesh to measure and nut out.


Thanks, I appreciate it. This will be a winter project so any snags/learning will be welcomed and enjoyed. I’m waiting on the owner to show a title and if/when he does I’m going to buy it. Again, I appreciate all the feedback. There will be a learning curve with this bike just like my A65 but I appreciate these old bikes and want to learn.

Thanks again everyone.
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