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Discussion Starter · #1 ·
Can anyone give me a definitive answer on whether or not a BSA A50 500 single Carb head can be used on an A65 650 cylinder without any other changes? I know it will bolt on,but I've heard its not that easy. AND I've head its no problem at all. I've run into three different opinions,but I figure this is where the experts are.
 

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Man that one doesn't sound good, but I never tried. Pistons have a pretty good dome, seems like they wouldn't fit up in there. Barrel AND head would work if same era, can't remember if rods are the same, crank is same except for flywheels, pushrods are shorter. No definitive answer answers here.
 

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I know that the 650 cylinder is taller than the 500 cylinder by 1 fin I believe. The stroke between both motors is the same.

I changed my A50 to a 650 by replacing the cylinder and head (and pushrods and cam) because the 650 parts were just cheeper to find. And really... who doesnt need more displacement. I also had to have the crank reballanced for the heavier 650 pistons.

But I agree that if the bore isnt the same between that the chamber of the 500 head might not be big enough to accept the 650 piston and major interferance will ensue. Would want to check that out 1st.

I have a 500 single carb head if you need one. And a single amal also.



 

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Discussion Starter · #4 ·
Ok,so its not a bolt on and go deal then..got it. The reason I was asking is because I have a complete A65,and an A50 for parts,and I was trying to cheap out and run a single Carb,since I have one that's pretty good shape. I guess it would be wiser,and cheaper in the end to just spend the money and get my amals rebuilt,or switch over to brand new keihins. I'm not known for my patience (or skills,or large wallet for that matter) Sometimes I don't think things through,and its guys like you who make me step back and think of the bigger picture. Thanks!
 

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yeah the dome will not fit up in the a50 head. it is noticably smaller.
 

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When I priced out 500 piston vs 650 pistons the 500 pistons were more than 2x more expensive than the 650 pistons. That was all I needed to hear.

Yea by the time I got done tracking down a used 650 head and cylinder, having the head rebuilt, cylinder bored, crank ballanced and new 650 pistons, pushrods and cam...I probably would of been better off just buying the 500 pistons...

but what fun would that of been :D

I went with the Keihn carb route also from Lowbrow.
 

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Can anyone give me a definitive answer on whether or not a BSA A50 500 single Carb head can be used on an A65 650 cylinder without any other changes? I know it will bolt on,but I've heard its not that easy. AND I've head its no problem at all. I've run into three different opinions,but I figure this is where the experts are.
I suspect that even if it would fit the compression ratio would be all to hell

better to sell the a a50 head and buy a a65 there are loads of them around

and go for a thunderbolt head, single carb bikes are less hassle than twin carbs with better mid and bottom end and better gas mileage
 
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