cylinder fitment question

[twist]

cylinder fitment question: what has to be done in order to fit a set of nickesil cylinders to a '77 R100/7? I am assuming it is not a direct bolt on conversion.

[Kurt in S.A.]

Beyond getting the sizing right, it should be direct bolt-on. If you want to buy new cylinders these days from BMW for a '77-on bike, it will be Nikasil. They don't make the iron cylinders anymore.

Kurt in S.A.

[Garnet]

Isn't there an issue with the cylinder base O ring?

To groove or not to groove?

[ME 109]

Isn't there an issue with the cylinder base O ring?

Yes.
They don't work.

That's why we always use a sealer on o ring type barrels.

[vanzen]

Bolt on ? NO.
More than just an O-ring ...
The openings of late engine cases are beveled to accept matching late cylinders.
Early cases do not have this machined bevel.
Late cylinders have a machined surface designed to help "contain" that O-ring.
This surface will not mate to an early case.
Machining of one or the other will be necessary
in order to properly fit late cyls to an early case.

[Kurt in S.A.]

Interesting...it's hard to keep all this stuff straight! I wonder why the slight change in the cylinder base...maybe it was to help with preventing oil leaks at the base??

Kurt in S.A.

[ME 109]

Isn't the bevel on the case just a lead in for the O ring?

[vanzen]

The cylinder also has a "ledge".
It is located on the base of the cyl.
below the bottom of the groove for the O-ring cut into the machined surface
which slips into the case opening.
And at the "corner" where this surface
and the machined flange which mates to the case meet.

i.e.
Machining of one or the other
(either the "ledge" removed from the cyl. bases, or a bevel added into the case openings)
will be necessary in order to properly fit late cyls to an early case.

[John Falconer]

Exactly!