Is this swingarm and tire placement correct?
By - mostlynotsketchy
Airhead swingarms and subframes have strange offsets to them by design. I mean, only Germans could justify having staggered footpegs...lol. From the rear of the bike, look straight over the top of the rear wheel at the backbone tube of the main frame - is it centered there?
That said, the swingarm can be adjusted side to side for center in the frame. If you're close to even on both sides at the pivot, you ought to be good. It takes some fiddling, but the exhaust can be tweaked so they look the same at both sides. Also, rear wheels have a few different spacers that were used over the years; make sure your spacer combo lets the brake drum/hub sit around 1/8" away from the flange on the rear drive housing. That way the rear shoes are fully on the brake drum surface, and you have maximum spline engagement.
EDIT: When you're reassembling things, use the string or straightedge method to check wheel alignment. Adjust swingarm position and spacers accordingly.
> only Germans could justify having staggered footpegs...
It's because of the cylinders.
I'm pretty sure they could've figured out a way to have the pegs even, if they wanted. Plenty of other bikes with longitudinal motors that don't need to have staggered pegs. Guzzis, Gold Wings, Honda CXs and STs, etc. It's just BMW being German about things.
Old triumphs have staggard pegs with a vertical twin engine. The engineering principal is based on, ' who gives a shit'?
Make sure to read carefully what is explained above.
The order is dissassembly (you will need to make/buy a thin-wall 27mm socket to get the lock nuts off the swingarm pivot pins); cleaning; inspection, re-grease, reassembly.
1st the swingarm is centered in the frame. This aligns the drive shaft correctly. It was fairly easy to get mine equal within .010" of each other using a dial caliper.
Then wheel is installed and the gap between the wheel hub and the final drive unit is checked. I don't have a value for the gap, but I can check my bike later.
There is no adjustment for centering the wheel to the sides of the swingarm (outside of re-lacing the hub to the rim), so if everything else is correct then your offset is, what it is.
frame is a 1974 R90/6
This is how I bought it. The wheel seems of center in the swing arm and too the exhaust. But, everything fits and drives fine.
This is my first airhead, not first restoration, and am working on an every-single-bolt restoration right now. This is the tear down. Powdercoating and restoring everything. Not a cafe project.
I have the exact same bike and others very similar to it. Yes, this is normal. One of the weird attributes of the shaft drive and drum brake on a double sided swing arm is that weird gap on the left. I love it and think it gives the bike unique character. Most people hate it or think it looks “unsafe.”
However…it still needs to be aligned to make sure the bike is stable, doesn’t drift, and doesn’t wear tires strangely. You can’t do this by eyeballing it. Multiple resources are out there. If you’re patient and prefer words over pictures like I do, Snowbum ( bmwmotorcycletech.info ) is awesome. Snowbum is batshit crazy, but he knows what he’s talking about unlike your favorite YouTube “specialist.”
Hit me up for more info. I love these bikes and have been working on them for a long time.
Has Snowbum gone nuts? Haven't needed to read his VERY long technical articles in years.
Also...we have to align our tear wheels? How!? It's all solid........a link to an article would put me in your debt forever. And I mean it.
Not the wheel itself, but rather the swing arm alignment in the frame.
If you look at where the swingarm pivots on its bushings on the inside face of the frame mounting point, you’ll see a small gap on each side. This gap should be measured with a caliper and adjusted so that it’s the same on both sides. You loosen the swingarm pivot bolts by popping off the black plastic cap, loosening the nut, and then turning the hex screw in or out. When you’re even on both sides you then cinch the hex screws snug (there is a torque spec, I do not remember it now) then retightening the lock nut (also has a torque spec) and replacing the covers. Wheel should be unloaded for all of this obviously.
This isn’t difficult, but it is time consuming and can greatly improve the way the bike tracks on the road. Done wrong, it can make the bike wander and drift so be careful.
Gotcha! Yeah, I've always been all over that.
The wheel is offset so you it mates with the drive system and you also can easily get it out if you’re on the side of the road while it’s on center stand. That’s why there’s a big gap on the side. That’s also why it’s important to get the correct tire size width wise, so it can actually come out without having to remove the rear fender.