Drive chain scraping inner primary

Hobot · Aug 15, 2011

1/16" is plenty of side room for a chain run, if the run is straight and sprockets not on loose supports, as is too common in C-do's gear boxes and swing arm bushes. I've read the tales of others for over a decade now, so when I fit 530 X-ring chain on Peel, if it rubs cases I'll let it till it eats a channel at least 1/16" to silent running. I will no longer run 520 width teeth on a cycle that makes over 45 lb ft at crank as not cost-effort effective for long.

DogT · Aug 15, 2011

Here's a pic of the gap between the swing arm and the inner primary, I flipped the image so it is right side around in the mirror. Like I say appears to be about 1/16" but the chain is pretty well centered between the gearbox and the primary with maybe 1/8" on each side. Really difficult to get a picture in there, that's the best out of maybe 15.

edit: got a better pic with the wife's cooppix, I could get it right in on the chain.

Dave
69S

Mark F · Aug 16, 2011

Nice shot Dave. That's incredibly clean in there.
Thanks.

DogT · Aug 16, 2011

I hope I can keep it that way. It's only got 250 miles on the rebuild yet. It used to be caked with inches of muddy oil. Just some slight oozes yet.

Dave
69S

Hobot · Aug 16, 2011

I more than gave up on chain lube I activity remove any not so much for the mess, which is a side benefit but mainly to slow the faster wear in our area of the grinding paste grit. It took me about 300 miles on Trixie to realize the leaky mess was d/t me over filling primary so chain was sitting fully in ATF instead of just barely touching it at rest. The Coolpix is really a handy camera/video and what I use last few years. Broke 1st one trying to get a shot after dark of the points in action, but found rebuilt one for $60 on ebay and worked at treat on the Gone Ridding post.

Pjr1440 · Aug 17, 2011

Hi guys, I had a look at my bike today, my problem is not the chain hitting the primary so much (although its a bit close for comfort). But if you are interested in a strange noise that sounded like the chain against the chainguard then have a read on a my new post on a slightly different topic!

post118808.html?hilit=scraping%20noise#p118808

thanks

Brithit · Aug 17, 2011

I've had std chains hit the inner primary, and others that didn't. On one (a '74 I don't have anymore) all it took was flipping the master link to the inside. I saw that tip in an ancient Norton News many years ago, and in this case it did the trick.

moorejm · Aug 17, 2011

I had this problem as well but the cause was a bent frame. The PO of my 72 Combat had neglected to tell me it had been in an accident. He had done the old trick of rotating a bent fork tube so the bike would go down the road straight. When I pulled the engine to put in vernier isolastics it was obvious that there was a problem. Whoever had straightened the frame had gone too far and had wienered it. The frame was bent enough that the isolastics were flattened on one side and the drive chain was hitting the primary cover.

Mick
72 Combat
73 850 Roadster
75 Triumph T160

john robert bould · Aug 19, 2011

maylar said:
Kinda like this?

Chain chewing into the chaincase, chips of aluminum in the links, a donut worn into it from the swingarm? Yup, BTDT.

In my case it was loose engine mount bolts allowing the engine to twist to one side and push the chaincase inward. Further investigation revealed oblonged and cracked crankcase mounting holes...

.. requiring a rather drastic solution...

I hope you're luckier than I was.

I have bought a Commando in bits, the back side of the inner cover is worn [chain rub] right through!
Is this a result of a badly worn swing arm bush? allowing the chain to slew over to the left.

Mark F · Aug 19, 2011

I have since heard that it could be 40 year old iso rubbers. After years of sitting on the center stand with the iso's carrying the full weight of the bike they tend to get a bit out of shape. This allows the motor and primary to do pretty much what it wants.
I think I am going to change to Mk3 iso's.
It's like opening a can of worms isn't it!

Drive chain scraping inner primary

Similar threads