BMW R80/7 rear crankshaft oil seal replacement

I could use some advice on this subject. I followed Moto-Binns (very
helpful UK company), suggestion to pull back the crankshaft before removing
the flywheel. (Removing the alternator stator and pulling a strap around the
front end of the crankshaft). This I think, is to stop the rear thrust
bearing from coming loose. However, after removing the flywheel, I found
that the thrust bearing had fallen backwards off its two pegs! It replaced
quite easily, I carefully pulled out the old seal and tapped the new one in
to the same position (flush to the crankcase), as advised because it's the
same length as the old one. This means of course that there would still be
space for the thrust bearing to dislodge, until the flywheel is bolted up,
and you can't see if this happens when you re-fit the flywheel. Re-fitting
is awkward with hardly any clearance to the clutch housing.
The flywheel felt and appeared to locate squarely and firmly on the end of
the crankshaft and the bolts seemed to tighten up evenly and solid, if you
know what I mean, and I seem to have the same very small amount of end
float. Should I still be concerned?
John

 

How much is a "very small amount"? 1mm? .1mm? There is always a little
bit of end play, or things would bind up.


--

Later,

Charlie

fix the e-mail address and it will get to me

 

Got no means to measure it. I would say that you can only just feel it. The
Haynes manual states 0.08 to 0.15mm. I would guess mine to be about right.
John

 

Don't have the manual handy, but it sounds OK to me. There must be
clearance for the heat expansion of the crank, and remember, it's
about as long as the pushrods.
Pragmatist - "R75/5 Forever!"

 

Do you think my thrust bearing is still in place?
John

 

That will be determined by the end play measurement. The function of the
thrust bearing is to control the end play, so it would stand to reason that
if you have the correct end play measurement, the thrust bearing is in the
right place.


--

Later,

Charlie

fix the e-mail address and it will get to me

 

Many thanks
John

 

I haven't tried this myself but you should be able to see/fix this
by removing the rearmost cylinder. I've never tried this myself.

http://members.rogers.com/sniderj/RearShim.jpg

When I recently replaced a flywheel I secured the crank by running
a piece of strap iron between the crank bolt and a couple of casing
screws. I did take a rough measurement of runout using a bracket, bolt
and feeler gauges. I really have to treat myself to a dial gauge. I
did not spend a lot of time agonizing about the spacer.

If you think you had the spacer in place and the crank securely
fixed then I wouldn't mess with it further.

On the BMW airhead list, there was a suggested method of measuring
end play with only the front cover removed.

"Ride the bike till it's hot. Remove the front engine cover, and fit
the dial indicator to read right off the front of the crank. Put a 6mm allen
socket into the rotor bolt and push back (toward the flywheel) as hard as you
can, while someone zeros the indicator. Now stop pushing, and stand up and
pull in the clutch. Read the indicator. You'll see a change of about 0.03 to
0.15 mm (I don't do inches so don't ask...)

"Add 0.03 to the reading if the motor is hot to the touch. Add 0.05mm
if it's just warm. This is a very reasonable approximation of the end-float
if the crank and flywheel were dry and oil-free.

"You want .10mm dry, which will be 0.05-0.07mm depending on engine
temp. On R100 motors I like it 0.02mm tighter, as it helps the clutch hook up
better. On smaller motors this isn't such an issue, and a touch looser makes
the motor a little freer."