primary cases

[wilko]

Anyone here have a set of swinging arm primary cases for a single and a set for twins for comparison? A friend needs a set for a B33 but the twin ones are more common. Just want to see if a sleeve arrangement could be made up to suit the single engine cases?

[Beezageezauk]

Hi Wilko,

One of the main differences is that the alloy inner primary case for the "B" series has a cut-out cast into the top of it.  This cut-out gives clearance to fit the magneto end cap.

Because of this your friend wouldn't be able to substitute a "B" series case with an "A" series one without some serious reconstruction.

Beezageezauk.

[wilko]

So I guess the chain line sits out further on a twin ?

[chaterlea25]

Hi Wilko,
The singles have a boss at the crank endas part of the inner case to space it out further than a twin case
but the twin case has a spacer to do much the same job
The single models have the chain 1/8 - 3/16ths further in than a twin
The reason for the cut out on the singles is to access the points on the magdyno
The outer covers are the same, thats why theres a thick section at the top of the outer case

HTH
John

[Topdad]

thats really interesting ,abit of info to be stored away, cheers john, BobH

[wilko]

I'm not giving up on the idea until I have one in my hand. Seems like a machined alloy sleeve could be made after all to make up for the raised boss at the back. 

[chaterlea25]

Hi Wilko,
Yes I have seen that done, Its a bit more difficult to incorporate the cut away portion for the magdyno
A set sold like that recently on fleabay

John