B31 and B33 Differences

[Nicky Burgess]

Hi,

I am currently stripping the engine on my B31 but it turns out it has a B33 barrel and cylinder head.  Does anyone know what ALL the differences were between the B31 and B33 ? Were there any differences in the cranks such as weight and balance factor ? Just as while its apart I would like to make all the necessary changes to turn it into a B33.   

Thanks,

[Pete C]

The cranks are different, cams, bearings, etc are the same.

Personally I would stay with the B31 crank as it is lighter and makes the motor a bit more sporty that a standard B33 thumper.

Finding a B33 crank might be a challenge as well.

[JulianS]

There were 2 different types of B33 crank, up to about 1953 with conrod marked part 66 483 (same marking on B31 rod) After then the B33 used a shorter rod marked 66 1614 and took a different piston as a result. The B31 rod did not change.

[Nicky Burgess]

So it shouldn't be an issue to run a B33 barrel and top end with a B31 crank ? providing I use the correct size conrod for my setup.   

I did read the flywheels are different between B31 and B33 with the B33 having heavier flywheels is this the only difference in the cranks between B31 and B33 ?