[G.Walker]

Hi Peter,

the twinport heads are the same. The only differents between the heads were the valve guides and the valve springs.
The valves had the same size but the valves of the M90 were alleged from a better quality.

I also believe that the racing models had a greater inlet valve as the TT90 models of the years before.

It seems to be that all M90 models had the 1 3/4 inch inlet valves. The 1 7/8 inch inlet valves were fitted in the racing TT90 models only.

Maybe can anyone confirm another well.

Best regards

C.

[peter wright]

I was wondering whether there were any physical differences between the model 9 and 90 cylinder heads for the period 1929-31.
I recently obtained a head from the estate of a friend who had owned a 1931 model 90. It would have been acquired as a spare for the 90 but I wonder whether this is indeed what it is.
I have compared it with a 1929 model 9 head that I have and can't pick any obvious difference.

Regards,
Peter