You are here:

Motorcycle Repair/Honda SL100 Swingarm

Advertisement


Question
Swingarm bolt left side
Swingarm bolt left sid  

Swingarm bolt right side
Swingarm bolt right si  
I am restoring a 1972 Honda SL100. While attaching the swingarm I noticed that it does not swing freely, which I am told it is supposed to do. However, upon examining the way it is (and is apparently designed to be) assembled, I understand why it binds. I have attached pictures showing the mounting of the swingarm to the frame and the connection points at each end.

I have had the frame and swingarm powder coated, but the powdercoat was masked and is not interfering with the swingarm rotation. I also removed the swingarm bushings prior to powder coat and replaced them with new bushings. I am quite sure the Swingarm is assembled to the frame properly since I took pictures before I removed the swingarm and it also conforms to the exploded view of the swingarm assembly from the various motorcycle parts websites.

As shown in the pictures (and the parts exploded view drawings), the swingarm axle is held on to the frame by a locknut on the left side and a exhaust pipe bracket spacer held with a cap nut on the right side. Both attachment points make direct contact with the inner metal sleeve of the swingarm bushing. When the nuts are torqued to 35 ft-lbs (the spec) it is easy to see why the swingarm will not swing freely since it is being pressed against axle with some force (not sure how the nut torque translates to force on the bearing sleeve, but it certainly is enough to to prevent the axle from rotating freely). BTW, when I loosen the nuts on both sides of the swingarm, it does swing freely.

My question is: is the swingarm NOT supposed to swing freely? Or am I missing something?

Answer
Byron, I understand your concerns, however the design of the swing arm bushings in these installations don't really allow for free floating movement at the pivot points. The swing arm bushings are rubber, not bronze or steel bushing types, so they just twist when the suspension goes through its travel. You do want to tighten up the nuts when the suspension is all installed otherwise, you might not be able to get the shocks back on afterwards.

If you want full suspension movement without the bushing interference, then I would buy a fresh swing arm lock nut and only tighten it up enough to prevent side-thrust and call it good. It was a design that is cheap and easy to manufacture and works on small bikes which have limited wheel travel. Ideally you wouldn't want a rubber bushing at the suspension pivot point as the can deflect to a certain degree on angle as well as fore-aft when the suspension is loaded by impacts from various directions.

Bill Silver

Motorcycle Repair

All Answers


Answers by Expert:


Ask Experts

Volunteer


Bill Silver

Expertise

Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.

Experience

I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

Organizations
VJMC (Vintage Japanese Motorcycle Club) of North America

Publications
VJMC newsletter, as editor for two years and as contributing editor currently.

Education/Credentials
3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

©2016 About.com. All rights reserved.