Print Page - A65 versus A50 cilinder

Title: A65 versus A50 cilinder
Post by: Gup holland on 23 Oct, 2023, 21:48

Due to shortes of A65 cilinders over here, is it possible to rebore an A50 cilinder block with liners in it to a capacity of 650cc ? I have A 1963 engine with 5/16 studs. I should say that all the bolts are in the same place, am I right?
Someone done this already, if possible?

Gr gup

Title: Re: A65 versus A50 cilinder
Post by: Allan G on 24 Oct, 2023, 14:39

short answer is no, the barrel castings are very different.

Title: Re: A65 versus A50 cilinder
Post by: Gup holland on 24 Oct, 2023, 21:54

Thanks for the short answer, I've never had a A50 barrel in hand to see the diverance.

Greetz gup

Title: Re: A65 versus A50 cilinder
Post by: Allan G on 25 Oct, 2023, 19:16

:) No problem

Title: Re: A65 versus A50 cilinder
Post by: DAVE BRADY on 27 Oct, 2023, 16:11

Hi,

You may get an extra bit of life from your A65 cylinders by boring them to take T140 pistons. STD T140 are 76mm with A65 being 75mm. So the T140 at STD is roughly A65 + 80 thou. The Triumph piston is 8.6:1 but as the crown height is shorter by about 2mm the piston sits a bit lower in the bore so the compression is less.

Dave

Title: Re: A65 versus A50 cilinder
Post by: Allan G on 28 Oct, 2023, 10:33

Hi Dave, 76mm is 40 thou on a A65 piston, but I'm pretty sure you can get +80 A65 pistons, as mentioned before you can try MAP Cycle.

http://www.mapcycle.com/categories/engine-top-bottom-end/pistons-rings/bsa-pistons-rings/bsa-pistons/19233-e-grp-bsa-a65-piston-set.html

Title: Re: A65 versus A50 cilinder
Post by: DAVE BRADY on 28 Oct, 2023, 10:40

Hi,

Yes, 1mm is 39.37 thou. It is the +80 A10 pistons I am getting confused with which seem to be a T120 +40 piston.

Dave.

BSA Owners' Club Workshop Discussions

The BSA Workshop => Twins => Topic started by: Gup holland on 23 Oct, 2023, 21:48