BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: Mike Farmer on 25 September, 2017, 15:16:55

Title: A65 Cylinder Head
Post by: Mike Farmer on 25 September, 2017, 15:16:55
Hi.

I have purchased an A65 Cylinder Head minus the inlet manifold and my thoughts are that the A50 and A65 are probably different

I am confused about this because although the A50 carb bores are different I cant find a definitive answer about the manifolds.
In one book they appear to be the same, another book says they are different and a further book doesn't even mention them.

So any light on this one would really be appreciated. I would also like to hear from any one who has one or has a cream crackered head they might part with

Mike :o :o :o
 
Title: Re: A65 Cylinder Head
Post by: JulianS on 25 September, 2017, 15:25:03
Parts books show A50 manifold part 68 223 and A65 manifold 68 224.
Title: Re: A65 Cylinder Head
Post by: Editor on 25 September, 2017, 17:02:32
Back in the mists of time, I had to replace the manifold on my Triumph 5TA as a stud had pulled out. The carb on these is a 7/8" instrument and found a 1.1/16" manifold at my local breakers (it was 1971). I duly fitted it and the bike would not run properly at all. Moral is, the manifold should fit the carb size or near as damn it as, if it is significantly larger, the space beyond the carb upsets the mixture and the fuel condenses out before it gets to the cylinder creating a damp squib type of bang apparently.
The Royal Star is 26mm the Thunderbolt is 28mm. Whether this is a large enough difference to create the same experience as the 5TA you never know, until you try it.
Chris
Title: Re: A65 Cylinder Head
Post by: Mike Farmer on 25 September, 2017, 19:21:35
Hi again. Thanks for your extremely useful replies. Really appreciated.

Mike :) :) :)