Rear Sprocket

pbmw · Feb 6, 2011

It would seem that my 850 Interstate rear sprocket is, um, how shall I say...knackerd.
It would also seem that the original designers thought it best that I should have to replace the rear drum brake every time I needed to change a sprocket.
Not quite sure what to think about that....except that it is a bit silly.
So, where to get one.
And...seeings as I have machine tools, has anyone thought of machining one to accept a bolt on sprocket?

britbike220 · Feb 6, 2011

This was discussed a short time ago and I believe it was quite an undertaking to drill and make a rear hub fit a removable sprocket, chain alignment and stuff. I also think it was determined buying a new one was/is cheaper. I don't know who makes the best one as I've not ordered a new one, but imagine all of the regular suppliers have them old Britts, AN, etc. I'm sure someone will post the details or a link to the thread.

Rohan · Feb 6, 2011

Since brake drums and sprockets have been integrated in Nortons almost since the 1920s, its also quite common to see the old sprocket machined off and new sprocket teeth brazed back on.

While this is quite the job for an expert, and getting the alignment correct is obviously important, it is quite possible.

If the chain is kept cleaned and well lubed though, the brake drum usualy wears out before the teeth, being good for several chains...

Hobot · Feb 6, 2011

I vote trash the drum and get new one. I also vote tame power use and start shopping for chain with can lift out valleys 1/3rd. As chain wears loose it rises on where it bares on teeth which too soon fan over or just turn to nubbins the chain passes over with noise but no tire turning : (

this is before I leaned about chain lift and switched out before just nubbins.

pbmw · Feb 7, 2011

Odd...
That's about what mine looks like.

Ron L · Feb 7, 2011

There were some poor quality Indian made drum/sprockets making the rounds several years ago, so I would recommend buying from a reputable dealer. It should still be cheap enough to not be worth the hassle fo trying to cut off the teeth and fit a new sprocket ring.

As Rohan says, the sprocket should last through several chains if maintained properly. Maybe a little less for pre-'71 with no cush-drive.

slimslowslider · Feb 7, 2011

The rear sprocket of my Mk3 is at the end of life.
I am in the process of fitting an alloy sprocket ring to the main body, a bit like on a BSA A65.
Have the alloy 520 sprocket.
Have the teeth off. The rear sprocket was already trimmed before for a 520 chain.
Have an idea how to do it but not final yet.
Have to fit some kind of back-up ring or bits where the bolts go.
Anyone done this before and how to do this in the best/lightest way?

Jeandr · Feb 7, 2011

Why not face that big iron piece and bolt the alloy sprocket right on without any modifications :?: By doing so, the next replacement will be faster (no machining)

Jean

swooshdave · Feb 7, 2011

It's been discussed here several times. I highly suggest you search and find the information. It will save you a lot of time.

Short version: Stock setup isn't that bad. Rear sprocket takes a long time to wear out with proper lube. Trying to graft on sprocket has been done but you have to up the teeth to make it fit. Old Britts has done it too.

Hobot · Feb 7, 2011

Norvil sells a large sprocket designed to be machine fit to drums. I had it done just to see how it worked out, terrible if not a hill climber need. I had drum teeth milled off with enough lip to seat the big sprocket ring on then had seam drill for half a dozen set screws to be able to switch sprockets and keep same machine drum w/o more welding etc. Here's a view of it and offer it up for anyone to play with on more reasonable sized sprocket, which would leave very little meat to tolerate the torque loads for long term.

britbike220 · Feb 7, 2011

Email Comnoz I believe he had the most info on the process last time and I think he's done this a number of times.

slimslowslider · Feb 7, 2011

swooshdave,
alas, I (again) did a search on "rear sprocket", went through all the 28 pages, but no new leads found.
Some on Mk1 and 2's but not on Mk3, apart from what Jim (comnoz) showed in a post in april 2009, but the photobucket pictures were removed.
I knew about the Oldbritts one, but for one thing would be expensive if only for freight costs, and than there is the fun of doing / messing-it-up ... yourself.
Also, although Oldbritts have used it with success on their racer, I prefer to have the bolts in some more meat than in the inner part of the sprocket body which is less than 6 mm thick over there.
But than again I do not know how the extra carrier is fixed to the sprocket body in the Oldbritts version.
Oh, and I prefer to retain a 42T sprocket.

highdesert · Feb 7, 2011

Generally speaking, anyway care to give a mileage estimate on the usable life of a Commando rear sprocket?

Some have said a couple of chain lives, but don't chains need replacing around 4000 miles or so, so a sprocket good for maybe 10K?

Assuming everything kept well lubed, normal street riding, no abnormal stresses.

britbike220 · Feb 7, 2011

I have used mine for 10 , almost eleven years and 24,000 miles and it is not in bad shape. I don't hot rod the bike at all and maintain it regularly.

Hobot · Feb 7, 2011

Well over 4 decades and 50,000 miles as my buddy Wes got out of his on non lubed plain chain but not wringing its neck out. I gave him a spare this fall because his teeth were getting thinned and almost fanned over. So ~ 5 - 10,ooo miles each chain change. Maybe 6-8 chains if changed when can lift links out rear valleys 1/3.

highdesert · Feb 7, 2011

Brittbike and Hobot, thank you!

Rear Sprocket

Similar threads