Pushrod Tube Rubbers

[Nourish]

I'm not sure if my stainless push rod tubes have been installed in far enough or perhaps I've used the wrong rubbers as they look like they are too compressed. My engine was a 90S but now with a '79 R80 crankcase so my gasket set was a mixture of parts - so how do you identify the 3 different type of push rod tube rubbers? - as I've got to lift the head again!

[Kurt in S.A.]

Snowbum writes there are two seals for the Airheads -

1970-1975 have 16 mm pushrod tubes, and the seal is 11-32-1-250-267
After 1975 they are 18 mm tubes, and the seal is 11-32-1-262-995

R65 had completely different seals as did the /2 era. Oak Okleshen sent me a figure which illustrates where the stop ring has to be placed for proper pressure on the seal. I kind of redrew it...hopefully you'll get the idea.

Hmmm...I can't upload the picture....it says "Sorry, the board attachment quota has been reached." If you can see things on the MOA forum, here was my post with the picture:

http://www.bmwmoa.org/forum/showpost.ph ... ostcount=8

Kurt in S.A.

[Nourish]

Thank You

[pkboxer]

I would think that you'd know if you fit the wrong ones as in pre/post '75 as the ID of the seal is 2mm different.

As for R65 seals IDK.

[Nourish]

When installing the rubbers do you fit them first to the pushrod tubes or into the crankcase?

[dougie]

When installing the rubbers do you fit them first to the pushrod tubes or into the crankcase?

If I recall correctly, on my R100 engine I put them on the tubes.
Tightening the head bolts compressed them into their place in the crankcase.
They had to be oriented the correct way with the line (moulded in the rubber) at 6 o'clock.

[Nourish]

Yes that's what I've been doing but they never fit in neatly - bits of them sticking out and not all of the rubber fitting in - it is better since I knocked the tubes back into the barrels a little.

[Duane Ausherman]

We started with the tubes inserted a bit too far into the cylinders. Then put the donuts on the tubes and installed the cylinders. Sort of guide the donuts in place as the cylinder gets closer. When the cylinder is tightened in place, then use the tool to tap the tube further into the case just far enough to compress the donut the right amount.

If it isn't far enough in, then it won't seal. If it is too far in, then the donut will be much too compressed and fail by splitting very quickly.