Primary Chain Adjustment

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Dogscout

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Oct 18, 2009
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Please tell me if I am understanding this correctly. Is the primary chain to be adjusted so there is slack of 3/8" movement with little to no force? Not that It can be moved only 3/8" by forcing it up or down.

I bought my 73 commando in 2000 and it has been an on and off again affair. It seemed to break one thing or another and eventually got stuck in the back of the garage. I never learned much about it other than taking it apart, replacing the offending part and then bolting it back together only to have trouble after the next ride. The last repair was a lifter loosing the stelite pad and I put it back together three years ago and let it sit. I am determined that this winter it is going to get sorted and one thing I need to do is get all of the adjustments sorted out.

So is my assumption on the primary chain correct? Is the slack determined like a drive chain? Only light to no pressure to achieve the 3/8"?

Yes its a simple question but this is the only bike that I have ever owned that has a primary chain.
 
I used to press up and down to check the slack,but found the clutch seems to bind slightly and I was told it was hard on your gearbox final drive bushings. I now just look and see the chain sagging about 3/8" without touching it. Works much better and no clutch problems.Better a little loose than too tight.
Bruce
 
Completely agree there, mine is just slack enough as not to hit the casing. Too tight & it is straining the bearings.
These chains never seem to stretch, it would start losing rollers first, but after many years.
 
Dogscout said:
I bought my 73 commando in 2000 and it has been an on and off again affair. It seemed to break one thing or another and eventually got stuck in the back of the garage. I never learned much about it other than taking it apart, replacing the offending part and then bolting it back together only to have trouble after the next ride. The last repair was a lifter loosing the stelite pad and I put it back together three years ago and let it sit. I am determined that this winter it is going to get sorted and one thing I need to do is get all of the adjustments sorted out.
Yes its a simple question but this is the only bike that I have ever owned that has a primary chain.
Click to expand...

I had a lot of issues when I first put mine back together (It was a basket case that had been apart 20+ years). It was frustrating, at first, to run it and have five things go wrong, then repair, restart, and have four different things go wrong. It took about three months to get everything sorted and learn the idiosyncrasies of the bike. It is worth it, IMO, to get through this period and get a chance to enjoy this machine.

As to the primary chain, 3/8" is the slack in the chain. This means you should see a slight droop in the chain on one side when the other side is taut.
 
Thank-you with a capital T.

I should start another thread with more questions, so after I fiddle with it this weekend expect more questions from this novice/noob.

Thanks again.
 
Fire away.There a lot of people on this site with loads of knowledge who would be more than happy to help you.
Bruce
 
If my rear wheel turns while idling in neutral on the center stand, I will loosen the primary slightly until the rear wheel no longer turns. This of course is dependent on good bushings on the transmission mainshaft.
 
If my rear wheel turns while idling in neutral on the center stand, I will loosen the primary slightly until the rear wheel no longer turns.
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This has nothing to do with primary chain tension, it's just oil dragging the gears in the gearbox, what makes you think slackening the primary chain would stop this happening?
 
This has nothing to do with primary chain tension, it's just oil dragging the gears in the gearbox, what makes you think slackening the primary chain would stop this happening?
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Because the primary chain pulls the mainshaft tighter against the bushes in the sleeve gear. Try it. If you slacken the primary, the wheel will stop turning. If it were simply the oil causing drag, it would not matter how much you slacken the primary chain, the wheel would continue to turn.
 
A couple things about primary adjustments. Whatever you think you've set the primary to, it won't stay that way for long if the trans isn't pushed back against the adjuster(s) and mounting bolts before you tighten things up. The trans is going to shift backward due to the higher tension of the drive chain, not matter how much you tighten the mounts. Set up the primay chain first.
Ron wrote:
Because the primary chain pulls the mainshaft tighter against the bushes in the sleeve gear. Try it. If you slacken the primary, the wheel will stop turning. If it were simply the oil causing drag, it would not matter how much you slacken the primary chain, the wheel would continue to turn.

This is how I know if I've got an over tight belt when it's hot. It works.
Ron, it's acting almost like a like a syncromesh ring.
 
If the primary is two tight, the when it goes in gear,the drive chain will snap. They are non- unit motors. Meaning separate motor and tranny. 50-65 hp is a lot. Revving a triplex with Norton torque1200-900 to put in gear .then going to a renold drive chain(510-520) it's c common thing who don't realize the unapproachable norton. Got my 1984-850 new in 74. Rebuilt everything,just finishing the carbs,14 yrs,second kick. Bike of the year five tears straight in Britain is no easy thing.
Lots of old smart,brilliant engineers. Keep at it. I have had 30 plus years and look forward to another 30 plus. The new 961 Nortons are 22,000$ with Harley trannys that suck. My two buds in England keep me up to speed .good luck,I'll help anyway I can. Bonesr@ iCloud .com Happy Holidays
 
bpatton said:
A couple things about primary adjustments. Whatever you think you've set the primary to, it won't stay that way for long if the trans isn't pushed back against the adjuster(s) and mounting bolts before you tighten things up. The trans is going to shift backward due to the higher tension of the drive chain, not matter how much you tighten the mounts. Set up the primay chain first.
Ron wrote:
Because the primary chain pulls the mainshaft tighter against the bushes in the sleeve gear. Try it. If you slacken the primary, the wheel will stop turning. If it were simply the oil causing drag, it would not matter how much you slacken the primary chain, the wheel would continue to turn.

This is how I know if I've got an over tight belt when it's hot. It works.
Ron, it's acting almost like a like a syncromesh ring.
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Hi Bob

I'm running a belt primary too and have it tensioned so that I can twist the top run through 90 deg. My back wheel also turns in neutral while on the main stand, how much slack to you have on your belt?
 
All adjustments are not very accurate if the trans sleeve gear bushes are worn out. :shock:
 
What ever you end up setting cold triplex too its very worth while to peek in at full temp to either confrim or refine your cold slack setting. Only takes one good heated over tension to bother shafts and tranny guts. Belts tight up with heat too and should be set cold for fairly easy 90' twist which is loose enough to put or and remove belt cold w/o touching adjusters. I verified my above trial-error finidins by quizing a world class drag bike builder with all sizes lenghts runs of belts, he adjusted all of em like above.
Belts don't stretch or take up shocks they transmit it and they need some decent tension not to jump teeth on a SNorton. Its another thread on whether to run oil or not and if so what of course. Ugh you are not going to hurt anything tugging by hand on triplex chain but sure can running in lower gears and enjoying much engine drag joys.
 
I just re bushed the gear box, installing a new mainshaft and adding a Maney out rigger. Not only was it necessary to slacken the belt, it also required trueing.

Chains are cake.
 
pete.v said:
I just re bushed the gear box, installing a new mainshaft and adding a Maney out rigger. Not only was it necessary to slacken the belt, it also required trueing.

Chains are cake.
Click to expand...

Was the work on your gearbox part of a refurb on the whole bike or was it because of a gearbox problem?
How could you tell the bushes were worn?
What were the symptoms?

My 73 750 runs fine with no signs of any problems until I read the thread about the back wheel going round with it in neutral and on the main stand now I'm thinking I may have an issue!

Cheers

Mac
 
Clutch wobble is the main issue with worn sleeve bushes, till shifting is bothered and damage to shaft rubbed raw occurs. Its no big deal if wheel turns some in N even if primary tension correct, just as long as so slight clutch plate drag a light hand on tire stops it.
 
willy mac said:
pete.v said:
I just re bushed the gear box, installing a new mainshaft and adding a Maney out rigger. Not only was it necessary to slacken the belt, it also required trueing.

Chains are cake.
Click to expand...

Was the work on your gearbox part of a refurb on the whole bike or was it because of a gearbox problem?
How could you tell the bushes were worn?
What were the symptoms?

My 73 750 runs fine with no signs of any problems until I read the thread about the back wheel going round with it in neutral and on the main stand now I'm thinking I may have an issue!

Cheers

Mac
Click to expand...
I have added a bit of power to the bike over the years and the only weak link was the gearbox. I had it apart a few years ago, add the longer sleeve gear bushes and knew then that i would need to do this work again, along with the mainshaft replacement.

Although the clutch hub did wobble a bit, it was still functionable. My main concern is the drivetrain integrity throughout.

My gearing was a little high and I have a desire to run the bike a bit harder. Adding a 19t sprocket from a 20t will get me to where I want to be. As long as there are no weak links in the powertrain, next riding season looks to be a good one.

I plan on a dyno test and maybe a track day at Grattan.

All that being said, if you are not sure of the condition of the internals of the gearbox, you're gambling. I don't mean to be hard but as easy as it is to get in and out of these things, there's really no excuse.
 
All that being said, if you are not sure of the condition of the internals of the gearbox, you're gambling. I don't mean to be hard but as easy as it is to get in and out of these things, there's really no excuse.


Hi Pete

No offense taken fella, I had the gearbox apart to check what layshaft bearing was in there a few months ago but never went as far as replacing bushes, the bearing got replaced and it's done around 750-1000miles since. The clutch drum has a wee bit of wobble but I've never really measured it till this thread came up so I might just have a wee looky again. I suppose the only way to see if the bushes are worn is to have it apart or is there another method or symptom.

Mac.
 
If not fitting a belt then clutch wobble ain't mush an issue to the chain nor tranny sweet function till bushes get so slack or broken up it tips cogs enough to smeer wear the shifter dog contact faces and shifting suffers. When able check shaft offset as they can sort of candy cane twist which beats snot out of bushes too soon again. 3rd gear teeth have been my weakest to let go and 1st gear bush worth keeping a spare on hand with pawl spring. If ya really think about-examine how oil can or can not get into the sleeve bushes it my change your style of routine operation.
 
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