Rear shock geometry

[bruce_launceston]

I recently had my YSS shock absorbers rebuilt because one had a leaking seal. The technician that rebuilt them said I should check all the alighnments because one shocker shaft had wear marks (he replaced both shafts).
As I have the rear wheel out at the moment I took the opportunity to measure the spacing of the shock absorbers. The top shock mounts are 240mm apart and the bottom mounts are 248mm apart, that's 5/16th of an inch for those not metric minded.

I wonder why BMW designed the R65 like this, is there an advantage or is this the only way they could fit them on. The rubber bushes allow for the slight splay but could this contribute to shock absorber wear?

There's something for you to exercise the grey matter on.

Cheers Bruce

[Barry]

So what you are saying is;

a is 240mm and b is 248mm

so that the shocks are splayed out at the bottom. I'll have to try and measure mine.

[bruce_launceston]

Hi Barry, your drawing shows it exactly.

There's no room for adjustment, it must be how it came from the factory.

I tried to measure it when I reinstalled the shocks but the mudguard is in the way. It can be done with my calipers once the wheel is removed.

[tvrla]

Would it be possible to spread the subframe 8mm so it matches the swingarm?

[bruce_launceston]

The seat probably wouldn't latch? but it's a thought.

At first I thought the wear on the shock shaft probably happened after one of the seals leaked.

[Barry]

I've been occupied to day replacing a broken spring on the car. Wouldn't wish this on anyone it's a struggle.

Anyway didn't get much chance to try and measure if the rear shocks are out of parallel.  What I did do is put a vertical spirit level on both shocks . Not very accurate perhaps but I think an 8mm error would be noticeable and I'm not seeing it.

I'll have another go when I get this damn spring in place.

[georgesgiralt]

Could the 4 mm each side to accommodate from the difference in position of the bushing ? Maybe the top one is thinner than the bottom one ?
My Fournales have spherical things to be able to mount the damper vertically even if the screw is not horizontal...

[bruce_launceston]

I had another look. There is no room for adjustment as 3 of the 4 shocker eye locations are a set width that just fits the shocker bush and sleeve. The 4th is the stud on the rear drive and the only possible adjustment would be outwards, exacerbating the difference.
The frame can't be spread as there is a substantial cross member just ahead of the top shock mounts.

Therefore I'm assuming this is the geometry they came out of the factory with.

Car shocks never seem to be vertical, they can be at much more extreme angles than this.

[Barry]

I guess as long is there is enough give in the bushes it shouldn't put too much side load on the damper.  Maybe you could take the shocks off and exercise them a little.