norsa1 wrote:The 850 Commando has eaten it's third rear wheel axle. Something is wrong but I am stumped. The rear wheel is an Atlas which does not have the rubber shock absorbers but I don't think thats the problem. The primary drive is still using the chain. The swingarm appears to be straight the axle assemby seems to be correct. IThe axle breaks right at the end of the thread where the axle bolts into the dummyh axle. Suggestions greatly appreciated.

KickStarter wrote:I am intrigued ...
How would I put in a one piece axle ?

Scott

comnoz wrote:
Common mod for racing or heavy loads. Basically you drill through the stub axle and use it as a spacer or make a spacer from bar stock. Then you go to the MC breaker and find an axle the right diameter and length. A lot of old dirt bike axles will work. You need to widen the slot in the left side of the swingarm and make it the same width as the slot on the right side. It makes tire changing a little tougher as you then remove the sprocket with the wheel. I have made up spacer sets in the past for people but I don't have the measurements anymore. Jim

As Mike and Frank, and others in the past have pointed out, it is a fairly
staightforward job to convert a Commando to a one-piece axle of same (9/16")
or slightly larger (17 mm) size. I used to race a Norton Production Racer,
and after breaking two-piece axles twice, did the same. I would warn
against going to a much larger diameter, however, unless you plan to modify
the swinging arm. As the bike progressed from a 750 production class racer
to a 920 Pro-Twins bike, I switched to 18" mag wheels from a TZ-250, and in
the process went to a larger 20 mm rear axle. To do so, I had to enlarge
the adjustment slots in the swinging arm to match. No problem, and it
seemed to work fine, until the swinging arm broke right through the
adjustment slot. It was kind of exciting, but at least I didn't crash. I
ended up makeing a new swinging arm out of rectangular tube, and all was
well from then on. I think it should be fine at 9/16" or 17 mm, but if the
urge to go larger strikes, think about beefing up the swinging arm. And
just to prove that you can never eliminate all risk, I also managed to break
one of the one-piece 9/16" axles during a race at Willow Springs. That's
actually what prompted me to go to the 20 mm axle. Didn't crash that time
either, but it was a wild ride off the track and across the dirt.

Ken Canaga

The axles tend to break where the threads begin. This is a stress riser
because of a fundamental design problem, so changing the manner of making
the threads (or the material) won't solve it. A threaded bolt simply is not
suited to take sideways stress at the the place where the threads begin,
and this is what happens in the axle, especially the cush drive version.
Best practices in aviation and other mechanical fields always have bolted
joints so any bending stress is on the unthreaded portion of the bolt.

Before I decided to convert to a one-piece axle, I mentally tried redesign
the two piece. The best solution would probably be matched tapers in the
axle and dummy axle, with threads only at the end of the axle to hold the
tapers together (some milling machine are designed to hold tools this way).
Steve Shiver's idea of redesigning the parts so the threaded section is
completely inside the dummy axle would also work, especially if the
unthreaded parts of the axle and dummy axle were a light press fit.

But it would be almost impossible to keep tapers or close-fitted
shafts clean enough in the environment of a motorcycle wheel axle.
Changing to a one-piece axle is the easiest solution, but there's not much
interest in it because people who ride sedately seldom have the problem,
and people who ride like hobot eventually tend to put on a different rear
wheel anyway, (as hobot did) because the stock one is so heavy.

Mike Taglieri miket_nyc@verizon.net

hobot wrote:About most tricky part is to retain speedo drive by drilling out its thin load baring spacer.