Low knocking/clonk coming from primary chaincase area?

I've noticed a knocking/clonking noise along with a little vibration that I'm almost certain is coming from the primary chain case area. It's actually difficult to pinpoint the source as it isn't loud and as it's only when I'm riding, wind noise etc drowns it out somewhat, but I'm fairly sure it's the primary. It doesn't happen when I'm accelerating, but only when I'm deccelerating or off the throttle and slowing down.

It's really only since swapping a 2mm clutch plate for an RGM 3mm (at the same time I did the clutch pushrod seal install), that I have noticed the knocking. I mention this because I didn't have enough thread to allow a gap for the seal with the washer, so ommited it and only used the tab washer - also only torqued it up to 40/45 ft/lb. I'll check that nothing is loose.

Perhaps the rotor could be loose too?

Perhaps the primary chain is a touch slack as it feels like a transmission snatch?



*This photo is from a few weeks ago, when swapping the clutch plate, and probably won't give any clues to the tightness of the chain, but I didn't adjust the chain at all. If I get chance today, I'll get the primary cover off and have a peruse.

Anything else I should be looking for/at?

'74 850 Mk2 and I'm using ATF in the chain case.

...at the same time I did the clutch pushrod seal install), that I have noticed the knocking. I mention this because I didn't have enough thread to allow a gap for the seal with the washer, so ommited it and only used the tab washer

Click to expand...

Clutch Rod Seal for Norton Commando
Part 1 - Installation

2. Measure the depth of your seal holder. Rev E depth = .130", identified by 3/4"hex across flats. Earlier Revs were 7/8".

3. Measure the length of the transmission main shaft that extends beyond the clutch center nut. (Also, inspect the end of the shaft for an irregular surface that may prevent sealing by the O-ring.)

4. The clutch rod seal holder must not bottom out against the clutch center nut. If measurement 2 is more than measurement 3 than see “fettling” below, otherwise continue...


Part 2 - Fettling
Frequently there is insufficient exposed main shaft length to allow the clutch rod seal to simply screw on without interfering with the clutch center nut. A variety of areas can be looked at to achieve the required clearance.

1. Check the alignment of the clutch basket sprocket with the engine sprocket, if to far out, correct IAW shop manual. (removal of shims 06-0894 .036” or 06-0895 .048”) DO NOT PUSH THE CLUTCH BASKET IN (out of proper alignment) FOR THE SAKE OF THE SEAL!!!

2. Use only one locking method to hold the clutch center nut. The tab washer 063459 is .043” thick and the genuine Norton split washer 063447 (040374) is .142” thick. The tab washer and loctite on the nut appears to work OK. NOTE, Earlier bikes (pre 73) did not originally come with the tab washer.

3. You may reduce the depth of the clutch seal down to .120” by grinding or filing.
Typically .140” is actually exactly two threads of engagement.


4. Last, you can grind down the thickness of the clutch center nut 060895 (04373) which is .375/.383” thick. Thinner than .350" would not be typical.

5. If by this time the clearance has not been obtained, I would recommend an in-depth investigation as to why the gearbox and engine shafts are so far out of alignment..."

Well you won't know till you open it up and look see, guessing is not much help, could be a few things as you have already mentioned not a major job pulling the cover off as you know.
Just get into it and open it up instead of guessing.

Two times i've heard rattles in there were from an inner primary bolt coming adrift despite new tab locking washer and proper torque (now using red locktite as well seems to keep 'em tight) and then the rotor & nut coming loose b/c the "pro" shop I paid good money to had left out the lock washer. Rotor was machining into the timing scale.

Bonzo said:

I've noticed a knocking/clonking noise along with a little vibration that I'm almost certain is coming from the primary chain case area. It's actually difficult to pinpoint the source as it isn't loud and as it's only when I'm riding, wind noise etc drowns it out somewhat, but I'm fairly sure it's the primary. It doesn't happen when I'm accelerating, but only when I'm deccelerating or off the throttle and slowing down.

It's really only since swapping a 2mm clutch plate for an RGM 3mm (at the same time I did the clutch pushrod seal install), that I have noticed the knocking. I mention this because I didn't have enough thread to allow a gap for the seal with the washer, so ommited it and only used the tab washer - also only torqued it up to 40/45 ft/lb. I'll check that nothing is loose.

Perhaps the rotor could be loose too?

Perhaps the primary chain is a touch slack as it feels like a transmission snatch?



*This photo is from a few weeks ago, when swapping the clutch plate, and probably won't give any clues to the tightness of the chain, but I didn't adjust the chain at all. If I get chance today, I'll get the primary cover off and have a peruse.

Anything else I should be looking for/at?

'74 850 Mk2 and I'm using ATF in the chain case.

Click to expand...

Have you had re- adjust your clutch since doing the clutch hub work ?
As in having a loose clutch lever that needed re- adjustment ?

Your clutch adjuster looks a long way out, is this a sign something is wrong? And / or could it be fouling the cover?

And, perhaps it’s just the angle of the photo, but are you sure the clutch diaphragm retaining spring is fully and correctly located in its groove?

The clutch diaphragm retaining spring does look like its not fully set in the groove, the whole spring has to sit in the groove on mine I always use a drift and lightly tap the last bit of retainer spring into the groove and the slot end of the spring looks like its level with the edge of the clutch drum.
Open the cover up and make sure it's completely set in the groove, could be your problem there and as you have said its made the noise since you put it back together.

I agree
It looks like the clutch circlip is out of the groove

I would not attempt to fit the spring while under pressure. Get the tool on it and then set the spring correctly. If you've never cleaned the basket groove, take a scribe and clean the groove especially the edges. Hope this is the issue!

Thanks for your input gents - and sorry no update, bit of a mad weekend.

I'll chime in later

Bonzo said:

Thanks for your input gents - and sorry no update, bit of a mad weekend.

I'll chime in later

Click to expand...

Don‘t talk to me about mad weekends.

Box of frogs here…

Use loctite on the clutch hub to shaft spline and the nut as well., The tab washer is too soft to stop the nut loosening off, stops it falling off but the tightness disappears after use if put on without loctite. The slight play between the hub and shaft plays havoc with this fastener causing it to come loose. Using loctite means that you have to use a puller to get the clutch hub off the spline when taking apart.

I took the above pic when I first took the chaincase cover off, but I snuck home for an hour and half lunch today and whipped the cover off for a peek.



I made sure the clutch spring was in the groove when I did the seal mod/plate swap.



The chain is definitely slack and I can get an 0.008mm around the rotor, but at around the 3 o'clock position it's tight.

I also spotted a bit of chain rub on the inside cover.



I haven't time to get stuck in now, but this looks like the source of the issue.

Yes, chain looks very slack and there’s a witness mark at the top of the chaincase.

The chain is definitely slack and I can get an 0.008mm around the rotor, but at around the 3 o'clock position it's tight.

Click to expand...

"Lucas call for a minimum air gap of 0.008″ to 0.010″ (0.2032 to 0.254mm) evenly all around between rotor and stator..."

I had thee same knocking sound. It was the rotor coming loose from the hub. I would check that also.

Please come back and share what you believe/find to be the problem...a lot of good guidance above.

I haven't had a chance tonight. The 'lawn' looks like the set from Honey I Shrunk The Kids and I've got something on tomorrow too.

I did order some rotor studs just in case one (or all) of these are bent.

Much to dissect here, a similar thread is found here: https://www.accessnorton.com/Norton...ing-inside-primary-drive-case-backfire.36259/ (you've probably already seen this...).

Knowing you got the spacers right for the backside of the inner primary cover, the sprocket lined up to the clutch basket teeth with correct spacing behind the thick spacer, and used a fresh circlip, right way in, firmly seated in the gearbox mainshaft groove, then we are probably not talking about a failed/failing circlip or misalignment causing the chain rub. From here, a proper check is to adjust the primary chain, then the final chain, and drop the bike for a test on both chains with full weight. Finally, have you checked the backside of the primary chaincase, rear, for scraping? Another indication of possible misalignment.

Hope it is the simple fix!