AJS/Matchless 350 to 500 conversion

[bulldog]

Sorry to upset the purists, but I am asking this question for my brother - honest!  

Could anyone tell me how easy/difficult it is to convert a 1955 350 AJS to 500cc's?

Many thanks

[willse]

Not difficult , but you'll need a barrel and piston , head , carb and exhaust , you may find that the crank balance factor is different too , so vibes might be a problem . Best of luck !!

[33d6]

Not quite as simple as it appears. The 350 flywheel is lighter than the 500. The balance factor of both motors is 65% so technically you need to have it rebalanced. The converted engine is rougher unless you do.
All this assumes both motors are 1955, it gets messier if the conversion parts are from a different year as these motors were continually updated in various ways and there are lots of minor variations to drive you nuts.
Its usually much easier to find a complete engine and change the lot. That way it doesn't matter if you have a later or earlier engine and you don't have to fiddle around having it rebalanced.
I've had two mates do the conversion but after the honeymoon period was over they both said it wasn't really worth the bother and next time they'd do a complete engine change.
Cheers, Bob