Piston Size

[aero]

Hi, does anyone know the size of standard piston on BS 90 Trail?
I know bore is 50mm. Trying to decide oversize or no. Will be getting
cyl measured today or tomorrow. Thanks again

[Mike Anderson]

Hi,
The service manual says bore to be 1.97 in. stock. I have never had one apart so can't say from experience, but that is what the manual states. Hope that helps.
Good Luck Mike

[Bikenstein]

Download a service manual here. Welcome to the site

http://bridgestonemotorcycleparts.com/index.php?action=downloads;sa=view;down=2

[Bikenstein]

Richard, owner of the site, has lots of nos parts in case you didn't know.

http://bridgestonemotorcycleparts.com/index.php?action=page;id=1

[aero]

Thanks, I have emailed Richard for prices. The 1.97 or 50mm is standard bore the piston must be
1.967 or so since clearance should be .0025 – .004 per the manual on this site.
Just trying to get idea of what I am going to need, std or .25 over. Will get head measured tomorrow.
Thanks again.

[Bikenstein]

Glad to help. Enjoy the site. There is an endless amount of knowledge on BS stuff here.

[disc_valve]

Hi,

The oversizes are +0.25mm and +0.50 mm. Measure the bore size witrh calipers and you should be able to tell from that if it's standard or re-bored.As an additional check, the piston crown was always stamped with the oversize (either "0.25" or "0.50"). Clean the carbon off the piston as the size stamping is quite light. No marking indicates a standard piston.

Graham