1950? 500cc BSA project

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harry76

harry76

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Apr 16, 2011
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I was checking EBay as i usually do when i saw a vintage BSA engine near the end of the auction and the price seemed too good to pass up and i could just see it at home in a boardtracker. So without much time for planning or to see if it was going to be usable i bought it. Its not like i dont have enough projects but seeing as its illegal here in OZ to ride an ICE bike i may as well build something with a little bite, and i just miss building bikes.

This will be a long project, and at this stage im just more worried about getting the engine going, and if i can get that far ill look at buiding a frame and getting an albion or similar separate gearbox. I dont plan on registering it, just a bike for my man room and car shows etc.

But for now im concentrating on the engine, and any help to get it going will be greatly appreciated.

As far as i can tell its a ZM20 engine number ZM20 4913. And if my research is correct that would make it a 1950 500cc model.

I only got the engine today but i will have a better look tommorrow.







 
harry76

harry76

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Apr 16, 2011
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Thats what i thought, so i had to buy it. Question is, is it too much engine? Its heavy, damn heavy. Should i get it going there will be little to no bicycle parts on this bike im guessing.

I really like the roundish shape of the bottom of the engine, i think it should fit nicely in a drop loop. And seeing as it would have a separate gearbox the profile of the engine is quite skinny. It is quite tall. Ill have to get out the tape tommorrow
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
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Harry, whatever you stuff that engine in it will tell you soon enough if it is strong enough! Proper engine mounts can make a lighter frame survive. Inadequete mounts and you can destroy just about any frame.
 
harry76

harry76

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I think i will definitely need to beef things up like you said. Ill have to make a frame, do you advise a certain sizing of tube and wall thickness for something like this? My brother races cars and builds rollcages for cars on the side so i can access his bender, and ill just tack it and get the guy he knows to tig it (i wouldnt trust my welds)

Would i need to go to a motorcycle steering tube rather then a bicycle one? I wonder if bicycle hubs/axles would be up to it (motocepane hub rear and sturmey archer or scooter hub up front)?

Also ill definitely need worksman rims/simplex tyres for this. I may have to get a set of Worksman rims, you sell them dont you Sportscarpat? I may need to get a set off you soon. I may get a few sets (if i can afford it) to keep shipping costs down
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
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harry76 said:
I think i will definitely need to beef things up like you said. Ill have to make a frame, do you advise a certain sizing of tube and wall thickness for something like this? My brother races cars and builds rollcages for cars on the side so i can access his bender, and ill just tack it and get the guy he knows to tig it (i wouldnt trust my welds)

Would i need to go to a motorcycle steering tube rather then a bicycle one? I wonder if bicycle hubs/axles would be up to it (motocepane hub rear and sturmey archer or scooter hub up front)?

Also ill definitely need worksman rims/simplex tyres for this. I may have to get a set of Worksman rims, you sell them dont you Sportscarpat? I may need to get a set off you soon. I may get a few sets (if i can afford it) to keep shipping costs down
Click to expand...
And the fun begins!!!!!
 
J

Jim C

Member
Jul 11, 2010
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It could be a 350 or 500 side valve single - you will be supprised at the power - it will tear up a bicycle frame and a bicyle rear hub. I would look for a older Champion flat track frame. It is going to be an exciting build and ride
 
Mr.B.

Mr.B.

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Oct 21, 2008
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I think you ought build it as a true motorcycle, wheels & all.

If Australia is anything like the States you can build a entire bike around the vin number on the head tube.

Find a junker parts donor frame & title and go for it.

-It will safer

-It should be able to be legal

-It would be a shame to invest blood, sweat, tears, and treasure into something you can’t even ride outside a parade.

I think this may actually be the natural evolution of some of the other talented builders on the Forum anyway.

My 2 cents.

What ever you decide, I’m looking forward to see what you come up with!

-Kirk
 
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harry76

harry76

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Thanks JimC, after picking it up i wouldnt be surprised at the power LOL

I know what you are talking about Mr.B, i had previously thought about doing what you said about a donor bike/VIN number, maybe i still will. It probably wasnt my smartest purchase but im fairly impulsive and now i have to live with the consequences.... then again if i can get this running im sure the engine would be worth a LOT more then what i paid for it....... I know a road registered bike would probably be the smarter direction to move but ive always loved board trackers, i am never going to afford one, why not build my own?

My initial plan was to have a bike with pedals, still a real MB but that all went out the window the minute i picked it up, my back is still sore :)

Ive still got a lot of thinking to do, but i dont wanna hurt myself so if the general consensus is this is dangerous ill happily change my plans or unload the engine. We will see
 
harry76

harry76

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Apr 16, 2011
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I also thought maybe its a waste to build a bike i cant ride on the road, but plenty of people build show quality bikes or cars (not suggesting mine will be show quality) that never see life outside of carshows and trailers...... the difference would be mine would have a price tag of a couple thousand (hopefully less) while the others are $50,000+

And providing i built it strong enough i may get a chance to use it at events our car club (monster car club) put on at a local racetrack and open up the circuit, or see if they have vintage speedway events and get involved in that.
 
wayne z

wayne z

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Dec 5, 2010
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Your engine is a lot older than the ones in the pic above. The above pics have standard carburators with intake valve operated by camshaft.
Your engine appears to have an atmospheric operated intake valve( no intake camshaft) and a mixer carburator common to older type engines.
Not nearly as much power and rpm to deal with as the newer versions.
.
The little pully was prolly to run a small generator for lights on the motorcycle.

I don't know what you paid, but with some info and the right listing might get you couple thousand bucks for it.
 
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Mr.B.

Mr.B.

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Oct 21, 2008
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No reason you couldn’t build your own BTR style bike.

Just Google image search “modern boardtracker” for hundreds of inspirations.

A while back I picked up a literarily barn fresh ‘73 Yamaha XS (XT) 650. I intend to use it for the basis a of retro racer.

You can get old 21” dirt bike wheels cheap, fronts with healthily brakes and just rims to lace a rear ‘tall wheel”

This could be the start of your best ever creation!

-Kirk
 
harry76

harry76

Well-Known Member
Apr 16, 2011
2,557
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48
Brisbane, Australia
wayne z said:
Your engine is a lot older than the ones in the pic above. The above pics have standard carburators with intake valve operated by camshaft.
Your engine appears to have an atmospheric operated intake valve( no intake camshaft) and a mixer carburator common to older type engines.
Not nearly as much power and rpm to deal with as the newer versions.
.
The little pully was prolly to run a small generator for lights on the motorcycle.

I don't know what you paid, but with some info and the right listing might get you couple thousand bucks for it.
Click to expand...
Thanks for the heads up. The lower engine HP and RPM suit me, im not after a rocketship. And if the engines older thats a bonus too, unless it means i cant get it going for lack of parts or other reasons
 
harry76

harry76

Well-Known Member
Apr 16, 2011
2,557
47
48
Brisbane, Australia
Mr.B. said:
No reason you couldn’t build your own BTR style bike.

Just Google image search “modern boardtracker” for hundreds of inspirations.

A while back I picked up a literarily barn fresh ‘73 Yamaha XS (XT) 650. I intend to use it for the basis a of retro racer.

You can get old 21” dirt bike wheels cheap, fronts with healthily brakes and just rims to lace a rear ‘tall wheel”

This could be the start of your best ever creation!

-Kirk
Click to expand...
I love XS650's and if and whn i do a street bike i plan on using that base and making a bobber..... there is actually a really nice XS650 board tracker, you may have seen it

http://www.google.com.au/imgres?q=x...1&tbnw=174&start=0&ndsp=18&ved=1t:429,r:0,s:0

If they are strong enough id prefer worksman rims/simplex tyres..... ive seen boardtrackers (like the one above) that have smaller diam wheels and they never look as good IMO. Id lace the worksman rims to motorcycle drum brakes if needed.
 
Mr.B.

Mr.B.

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Oct 21, 2008
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Oh yeah, I’ve seen that one!

I especially like the aluminumness of it, in fact like it I bought 21” aluminum DID rims for my project. The front drum has 148 x 25mm brake shoes.

btw: 21” motorcycle rims are actually 22” across compared to 26” bicycle’s 21.5” Not to mention the quality and quantity of available tires.

-Kirk
 
harry76

harry76

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Apr 16, 2011
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Brisbane, Australia
Are you saying that the 21" motorcycle rim is actually a larger diam then the 26" bike rims? I did not know that , thanks.

Well im sold on that, and itll definitely be cheaper as i would have had to pay for freight from the U.S for the worksman rims, and that alone would likely have been more expensive then my engine.

Are you referring to the 21" rims they use on the front wheel of MX bikes?

Thanks again, this information will help a lot.... off to the motorcycle wreckers i think :)
 
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