Sherpa 175 Model 221 Swing Arm and Rear Wheel Issues

[gjscott]

Sherpa 175 Model 221 Swing Arm and Rear Wheel Issues

My rear wheel is offset about 17mm to the right in the swing arm.

The wheel spindle is parallel to the S/A spindle.

Maybe the  whole swing-arm is bent to the right?

Maybe the rear wheel has been re-laced and the offsets are not correct. 
Left wheel offset 40mm from sprocket mounting face.
Right Wheel offset 35mm from hub edge. 

What's going on?????

 

Edited November 27, 2019 by gjscott
typo

[trialsrfun]

Is the chain lining up correctly over both sprockets, place a straight edge across the side of the rear sprocket towards the gear box sprocket also.

[gjscott]

24 minutes ago, trialsrfun said:

Is the chain lining up correctly over both sprockets, place a straight edge across the side of the rear sprocket towards the gear box sprocket also.

I can’t check as the bike is stripped, but the rear sprocket has noticeably more wear on the inside suggesting that it is offset to the right of the front sprocket. 
This supports the swing-arm being twisted to the right. 
 

So how do I straighten a swing-arm?

Edited November 27, 2019 by gjscott
Typi

[b40rt]

15 hours ago, gjscott said:

I can’t check as the bike is stripped, but the rear sprocket has noticeably more wear on the inside suggesting that it is offset to the right of the front sprocket. 
This supports the swing-arm being twisted to the right. 
 

So how do I straighten a swing-arm?

If its only a small twist, adjust the snailcams until the sprockets align, ride and enjoy.

[gjscott]

6 minutes ago, b40rt said:

If its only a small twist, adjust the snailcams until the sprockets align, ride and enjoy.

Problem is that the swing arm bush housing aren't aligned either.

 

[b40rt]

Have you spoken to in motion, they maybe have a spare one for sale. I think you would need a jig and Oxy acetylene to straighten your current one.

[trialsrfun]

4 hours ago, gjscott said:

Problem is that the swing arm bush housing aren't aligned either.

 

The sketch makes it clear.

If you could take the swing arm with its spindle and wheel spindle to someone with a workshop who understands motorcycles they should be able to realign it for you. Roll both spindles across a flat surface to check that they are both straight.

What area are you in? 

Edited November 28, 2019 by trialsrfun

[gjscott]

My swing arm is bent in quite a complex manner, simply put it's like a parallelogram when it should be a rectangle. As I don't know what most of the dimensions should be, and as it will need to be jigged and pulled the repair is beyond the resources I have available. 
So, I need to replace it. 

Question, do I try to get another 221 swing arm, which required modifications to both the swing arm and bushes to fit replacement brass bushes, or do I use a swing arm from another model?

Next question, which other models will be compatible?
 

Edited November 29, 2019 by gjscott

[feetupfun]

What you are looking for is any model Alpina or Sherpa T after the time when they changed to using the rear engine mount as the middle support for the swingarm axle.

 

[scot taco]

i would guess that in the way that it is bent you also need to check the rear engine mount were the swing arm bolt goes through it. the I.D. could be worn out of round and sloppy. also the width of the bushing in that engine mount could be worn making it a loose fit in between the swing arm. I believe Inmotion has new rear engine mounts. Also have a look at the holes in the frame for the swing arm bolt to see if they are sloppy.

[sherpa325]

I would check the wheel spacer as these are not standard and were used to replace the speedo. Mine are 33mm but I have seen quite a few variations, smaller and bigger, and yours does look a little small to me, but difficult to tell. Any reasonable fabrication shop should be able to straighten it, after all its just steel, which can be heated straightened, welded all quite easily. They did bend back in the day and we used to straighten them in the bike.

Cheers Greg