Front sprocket replacement...and other ?'s

Hello!

I've searched the forum archives looking for some advice on changing the front sprocket but haven't really been able to key the right thread if one exists. I'd like to go from a 19T to a 20T. The only manual I have is the factory manual and it is pretty ambiguous. How do I go about replacing the front sprocket??

Do I take the gearbox out and replace it from there, or does the primary case somehow come off and I go at it that way? The book doesn't really explain. This probably seems like a stupid question, but I'm really not sure what to do. Aside from the obvious gearing difference, is there any adverse affect on the bike by changing the gearing this way?

Also, my bike has the original Isolastics that I really don't know how to set up correctly. The bike is squirming all over the place so I'm pretty sure something is out of whack. Assuming money is a BIG object, is it better to swap the headsteady for something modern, or switch to the adjustible MKIII mounts?? I could only do one of those this time around. Or is it possible (and likely) to get it handling well with the stock engine mounting system?

Thanks in advance from a newbie!

You will need to take the inner and outer covers off. Be sure to have all of the seals and gaskets first.

I recommend that you fit the new adjustable isolastics as a first step to improving the handling and more importantly subsequent ease of adjustment, for this job you will need to remove the primary drive system and inner cover - do make sure you have the correct tool for dismantling the clutch, or else serious injury can occur! You will also have to remove the gearbox and gearbox mounting/isolastic mounting. This will be an ideal opportunity to change the gearbox sprocket. While you have this apart check for play in the swingarm, often it is not the bronze bushes that wear, but the shaft itself wears the bore hole in the mounting slightly oval, there are a couple of fixes for this including boring the hole bigger and fitting an oversize shaft, fitting the Heinz Kegler clamp fittings, or welding some nuts onto the outer part of the shaft and fitting bolts to support the shaft. You can check where any play might be by grabbing the outermost extremity of the rear wheel and moving it back and forth while looking for any play (there is a slight natural amount of play in the isolastics, but there should not be any 'clunking'. You can leave the engine in place for these operations, but you will have to support the bike on something under the frame as the centre-stand comes off together with the gearbox/isolastic mounting. I would agree with Hortons Norton and order all of the relevant parts prior to dismantling. The front isolastic mount should be changed at the same time and is quite straightforward.

Hi Southplains,

You didn't state the year of your bike, but since you'e talking about upgrading isos, I'm assuming it is pre Mk3. i don't recall such a problem on my Combat, and I don't believe a squirrilly front end is something you should expect from a well-set-up Commando regardless of age or model; these bikes are smooth rides. First, check the date code on the tires. If they are more than 7 years old, or, even worse, have NO date code, put on some new rubber ($85 per tire from many online suppliers). This is an essential safety issue, but will also settle down the front end. I understand the budget constraints, but old rubber is DANGEROUS. While the wheels are off, replace the bearings (cheap insurance and easy to do). True the wheels (you can do this in place with an indicator) and balance them (you can do a very rough balancing in place if your bearings are good, otherwise use a balancing jig). The idea here is to remove the more obvious front wheel deficiencies before having to address the hard stuff.

Horton is correct, removing the sprocket requires the removal of the entire drive train, including the inner cover. It's a full day's job. And then you've got to put it back together.

I don't believe that you have to upgrade your bike to get it to track well. Just work through it and replace the bum components.

Handling issues as you describe can be due to worn swing arm spindle and bushes. With the bike on the center stand, grab the rear tire and push side to side. If you feel a lot of movement it's the spindle. These parts wear if the bushes run dry or someone has lubed with grease instead of recommended gear lube (140wt is specified). Very common with Commandos.

Pre MkIII isolastic adjusters (shims) work just as well as vernier adjusters (MkIII). Shims are a bit more difficult to adjust however. Adjustment is for either is very well described in the factory workshop manual.

If you are doing a sprocket look on oldbritts.com under technical section.
Fred shows the ratio's for each sprocket.
I have a 72 combat 750. I'm leaving the 19 tooth until I need to remove the clutch.
For the efforts involved I'd opt for a 21 tooth minimal if goin to that trouble.
I'm also passing on the 520 chain conversion just don't think it's worth the $ to me for whats involved.
The guys on here are right. When I got my bike w/ 8,000 orig miles the pfte washers were gone?
Opened up the gaiters and dust came out. I guess they rotted off?
I knew something was wrong as the motor moved to and fro on the centerstand as I turned the handle bars
left and right.
You can replace these washers shim up to .010 on opposite sides as manual shows. This will improve handling
immediately.
Next get the front rim balanced and trued and a new tire. My 37 y/o Dunlop's are hanging in my garage for posterior
reasons. Old tires are a death trap. A litlte drizzle and right down you go. My front tire looked new but nearly had to be
saw zalled off the front rim it was so hard. Old tires = no traction when wet = crash
A later 850 box head steady is a nice driver improvement. If your not lookin to get sparks off your foot pegs
the stock 850 head steady is fine. I replaced my cracked 750 one w/ a new 750 one w/ new buffers.
It lets me get frisky w/ her but I'm not riding like a formula 1 jockey.
I guess you should brain storm the bike. Are you going to enjoy it like I do and keep it a facsimile of Wolverhampton
English thinking or are you going balls to the walls as some have and recreate the Norton.
They were soaked in racing history so you have a promising platform to go where ever your heart leads.
Ask lotsa questions I do :mrgreen:
Marshal Norton
72 combat, 95 E-Glide, 70's beach bike, when all else fails 10R black Cadillacs

southplainsdrifter said:

Hello!

I've searched the forum archives looking for some advice on changing the front sprocket but haven't really been able to key the right thread if one exists. I'd like to go from a 19T to a 20T. The only manual I have is the factory manual and it is pretty ambiguous. How do I go about replacing the front sprocket??

Click to expand...

First of all, where do you live? People on the list are all over and would be more than happy to guide you through the first stages of Commando learning. Google INOA and find the chapter near you and send out a shout for help.
Manuals a nice but parts diagrams make everything much easier. Click the little diagram at the top of each parts group at Old Britts and it gives you an exploded view of it all, with parts numbers, you'll need'em, along with the proper names for things. You'll never notice the difference in one tooth on the front sprocket. To be honest, this'll cost you some dough and it sounds like the handling issue is probably more important. Besides, you're not going see the ton and live to tell about it till you get the handling squared away anyhow.
http://www.oldbritts.com/ob_start.html

southplainsdrifter said:

Also, my bike has the original Isolastics that I really don't know how to set up correctly. The bike is squirming all over the place so I'm pretty sure something is out of whack. Assuming money is a BIG object, is it better to swap the headsteady for something modern, or switch to the adjustible MKIII mounts?? I could only do one of those this time around. Or is it possible (and likely) to get it handling well with the stock engine mounting system?

Thanks in advance from a newbie!

Click to expand...

Ill fated is right. MkIII adjusters aren't any better than the shims. I hate MkIII iso adjusters. They're a lousy design and the materials are junk. (Whew! I feel so much better!) Mick Hemmings has a set that has the threaded male part of the adjuster as a stationary spacer on the mounting bolt with the threaded adjustable collar free to adjust with no loading. You don't have to have the front Iso machined and if you have OCD you can get a set for both sides and actually move the cradle around get things just so. But first of all find your local Commando mullas, bring good beer and the knowledge will flow.

Thanks for all the great replies! I really do appreciate your taking the time to respond.

I live in Lubbock TX so if anyone here is nearby let me know! I'd love to meet a few more people who ride Norton's (or any old bike for that matter.) Seems like this city is lacking what San Diego (my last hometown) certainly has.

I don't ride like a wild man so I guess I'll stick with the stock headsteady. I can't believe that I completely have overlooked the tires!!!
You guys are totally right, mine have been on there since I bought the bike (5 years ago) and have been on there god knows how long! I'll get some new ones before I ride again.

My bike is a mix of years. The frame is a '71 with all the '74 guts. Disc brake and dual Amal's. Engine runs pretty good as I've done quite a bit of work there already. Still tons of issues with the bike and I really am not all that sure of myself with getting this thing on the right track. This site is awesome though.

I'll make absolutely certain that the shims in my bike are correct and then see where that gets me. Thanks for the help with the sprocket, that will be a winter project.

southplainsdrifter said:

I live in Lubbock TX so if anyone here is nearby let me know!

Click to expand...

Be sure to update your profile so your location is apparent in every thread. >>>>>
:mrgreen:

This is a pretty good explanation of the process, tools required, and some tips:

http://www.nocnsw.org.au/sprocket.html

Thanks, that website is perfect.

You're certainly welcome; yes, I've used their instructions a couple times now. BTW, during one of them I replaced the 19T that was on there with a 20T, and I haven't noticed any difference.

There's a thread here someplace that describes building a clutch spring compressor tool out of an electrical junction box, a bolt, and a couple of nuts.