Re: B31 400cc

[Bess]

Hi,
    Has anyone converted the 350 into a 400cc,  if so what parts did you use and was it worth it?

Many thanks...

[paulm]

yes i have you need a T140 piston and a standard b31 compression plate

[Bess]

Hi,
     Thanks, is it a standard piston and what compression ratio?

Best wishes...

[Pete C]

use the low compression T140 with shallow dome. In the Bonnie CR is about 7.5-1 however, it is a lot higher when fitted in the B31. I initially used a standard T140 piston and it pinked horribly, even with a decompression plate.

You can also modify the piston a little if you have a lathe. I can send you the details if you want to go that way.
I am currently running mine with a 5mm deco plate and it is very easy to start and runs well. I may try a thinner one next time the barrel is off for any reason.

I did fit goldstar type valve guides and GS touring  cams which made it a bit livelier (and louder) but I'm back to standard now.

I think the conversion is worth it and it doesn't cost much, B31 barrels are not that costly.

have fun
Pete

[Bess]

Hi Pete,

           Many thanks for the information, most helpful. If you could send me as much as you can I intend to go the 400ccmso I value peoples advice and help.


Thanks again...

[Pete C]

sent you a PM