Cylinder machining
 

If you want to fit 90mm (or is it 89mm) RS cylinders in an early case to make a 2.5ss, it's said you have to machine the spigots. Though that's not recommended for the mag cases- bad from a strength and originality standpoint. So that being said, can one machine the cylinders instead to be a slip fit?

JMHO, but you can safely machine the 90mm spigots to 92mm for the 89mm-90mm cylinders.

You do NOT want to make the cylinders into slip-fits due to cracking issues.

Thanks for the response, Steve. This is a 2.2 case, however. Are nickies (89mm slip fit) a better option or do they experience cracks as well? Or is it a pick your poison, kind of deal?

I've not used those Nickies, but my experience with thin-walled cylinders isn't good so tend to avoid them.

Having done quite a number of these types of engines over the past 35+ years, I've not seen any issues specifically related to opening these spigots from 90mm to 92mm. There are other problems with the pre-5R cases, however it has nothing to do with spigot diameters,...:) :)

Ultimately, it depends on the engine's configuration and type of use.