balancing carbs on R90/6

First, I'd check in the genuine workshop manual (or with
someone with access to one) if this is a fault. I know that
there has been BMW bikes where this was how things
were meant to be.
If it should need correcting, there is a minute possible
adjustment by tightening the swing arm bearing on one
side and loosening on the other. This is of course limited
by the need to have the driveshaft line up with its
tunnel in the swing arm.
Any other correction would be by truing the frame and
you need a real specialist to tackle that job.

Generally, you don't do wheel alignment checks on
shaft drive bikes unless they have been crashed. There
are no adjustments so normally alignment does not
change. And if it's wrong, there is nothing a mere
mortal can do to correct it.

 

There are a couple of things which could be going on.

As you point out, there's the alignment of the swingarm in
the frame. At a guess, you might find 1/4 " clearance on each
side between the arm and frame with the spacing providied by
the swingarm pivots. I wouldn't touch these unlessI had
the torque specs to set the bearing correctly.

On the R90, the rear wheel is (I think) splined and slips
into the final drive. Not sure what spacers might be involved
here, but another potential source of misalingment.

Finally, the OP speaks of play and wiggle in the wheel
and/or swingarm. This is something I'd really worry about
until I really understood it. Any kind of failing bearing could
make for a really scary situation, and if it's failing it can
fail quickly.

 

The bearings are not the problem, they are conical roller
type and you just snug them up. The Herr Doktor Diplom-
ingeniör who wrote the manual might make it complicated
enough to be rocket science but in reality you just need a
little bit of feel for what you do.
The problem is the clearance for the driveshaft.
And, like both you and I said, there is no chance to find
half an inch here.

I'm speculating too and I would be very surprised if there
was a spacer. And at least to me a hub that was in the
wrong position relative to the final drive housing would
look very obviously wrong. The rear axle would be very
short on one side as well. But some people don't seem
to notice such things so I guess it could happen.

I totally agree!

 

On the single sided swing arms, there's a preload torque
and a final torque, both farly small. The two sided swingarm
may be a little less fussy, but I'd be careful there, again because
of a concern about failure. On my paralever, you could probably
find 1/4 " there if it were pushed all the way to one side instead of
cenetered. (about 1/2" total space).

At the BMW 49er rally, I happened to wander into
the repair facility and catch part of a rant on this subject.
The bike had a two leg swingarm and had apparantly
been put back together slightly wrong, such that the
wheel was a little off and the brakes weren't quite centered
in the drum. Part of the rant included spacers, possibly
homemade.

If it were me, I'd seek a good local mechanic to inspect and
advise. An inspection would be money well spent.

 

Online parts fiche:

http://www.ascycles.com/Illustrated_catalog/R90_slash6(74-76)/catalog_frameset.html

Hope this helps.

 

Thanks for all the advice guys. I may take it in to a shop. I just
got that shock bushing in today so I am gonna put that in and I'll tell
you how it goes. But meanwhile, I have another problem. The clutch
wont disengage. There is hardly any resistance. The clutch hand lever
does activate the lever down near the gearbox. I looked in the manual
and it there is a rod connecting the lever to the clutch plate and
spring. I think that may be the problem. Any ideas? I looked in my
clymer manual and it doesn't seam to hard to get the gearbox out. I
might try it this weekend. Thanks.

 

To completely remove the tranny I think you'll have to either
remove the swingarm or slide the whole engine forward.
Not 100% sure on your R90 but true on mine.

Besides the throwout rod, there's a bearing in there.
My first bet would be a problem in the throwout bearing.
There could also be some problem where the rod pushes
against the diaphragm spring. The R90 clutch and
and flywheel are different than mine, so I'm a little
fuzzy on details here.

If you decide to go after the clutch, a couple of suggestions.

1) Do not hold the flywheel gear teeth with a screwdriver. Bad shit
happens. DAMHIK. Use a hunk of scrap metal to bolt the
flywheel and clutch housing to the engine casing and hold
it steady.

2) Be careful how you remove the clutch bolts. You need some
longer bolts to hold the clutch in place so it doesn't spit parts
at you when you loosen the last bolt.

3) Per the manual, clutch bolts and driveshaft bolts should be
replaced and torqued carefully to spec.

4) Get some long bolts or threaded rod to thread into the
boltholes for the bolts holding the tranny to the engine.
Makes it easier to slide the tranny away from the engine
using the bolts or rod as guides.

Good luck. RTFM and go slow and carefully.

 

Hey guys. Well, i've been working on it for a couple days, going slow
and I have the transmission out. I guess now is the hard part. Have a
few unrelated questions though. I'm trying to get the rubber bushing
out from the right shock to replace it. It consists of an inner metal
bushing, rubber, and an outer metal bushing. The outer metal bushing
is really stuck in the shock. I suppose i might need a press to get it
out. Any other ideas? Also, when I removed the rear wheel, one of the
bearings fell on the floor and got some dirt on it. Think it will be
ok to clean it and brush it off in kerosene? Thanks

 

I'd check a BMW-specific resource (e.g. the iBMWR list or a BMW
mechanic) for information before I tried anything, but then I'm cautious
that way.

What sort of bearing is this? A needle or roller bearing? Generally,
cleaning in kerosene or similar solvent is the recommended course of
action for non-sealed bearings. If it's a sealed bearing, then solvents
shouldn't be necessary.

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

Have you got the replacement part in hand already ?
I wouldn't try to remove the old one until I had the new one
there to examine and to install.

Lots of times you can use a socket wrench or a ground to
size washer to remove a stuck part. You can often use
a hammer and drift, a nut and bolt or a clamp in place of
a press. If a press is needed, any shop can do this
cheaply.

To cut a washer down to size, I've spun it on a bolt chucked
in an electric drill and ground or filed it down. You should be
wearing goggles if you try this. When the washer is the
same diameter as the part you're trying to remove, a
nut and bolt can be used to pull the part. I've used this
trick on paralever bearings.

It's also OK to do a destructive removal as long as
you confine the damage to the part you're removing
and you're sure you have the replacement.

If you clean it, you have to re-grease it. Mobil 1
synthetic grease is a good bet for most applications.
As others have pointed out, if it's sealed, you shouldn't
have to clean it.