cNw #101 Norton Commando 850

Yeah, all silencers are pretty much aftermarket now for Commandos. A little interesting in that the left side seems to have more stress due to vibration on Commandos. Keeping the exhaust pipe rose nuts, muffler clamps tight and silencer mounts tight and rubbers fresh is part of the maintenance. The engine vibrates about in the ISO's, but the silencer mounts are solid mounted on the Z plates.
 
Deckard said:
Yeah, all silencers are pretty much aftermarket now for Commandos. A little interesting in that the left side seems to have more stress due to vibration on Commandos. Keeping the exhaust pipe rose nuts, muffler clamps tight and silencer mounts tight and rubbers fresh is part of the maintenance. The engine vibrates about in the ISO's, but the silencer mounts are solid mounted on the Z plates.
Click to expand...
It was the right that went on mine. Everything else is as it should be including the rubbers which are still nice a flexible. These were fitted on the build in 2013, 12500 miles ago. Matt no longer uses this supplier but he didn’t say why; he now makes his own which have his logo on one side so reversible to show or not show. Don’t know when the change occurred, I wonder which are on @robs ss bike?
 
Deckard said:
Yeah, all silencers are pretty much aftermarket now for Commandos. A little interesting in that the left side seems to have more stress due to vibration on Commandos. Keeping the exhaust pipe rose nuts, muffler clamps tight and silencer mounts tight and rubbers fresh is part of the maintenance. The engine vibrates about in the ISO's, but the silencer mounts are solid mounted on the Z plates.
Click to expand...
they should be rubber mounted to the Z plates as standard.
 
Just when I thought I could relax and enjoy the ride…

Okay, so yesterday I decided to brave the cold and enjoy the sun on nice salt free dry roads. 2nd kick and within a mile perfect idle without adjusting the FCR idle speed, perfect.

20 minutes later, 10 miles down range, one of my favourite local roads was clear time to scoot on a bit. Then accelerating half throttle in 3rd at approx 4k rpm and loudish ‘chirrrp’ from underneath me, or at least that’s my perception with custom earplugs with an open face helmet, WTF? Beyond and below 4k nothing. At no point is there any loss of power or any change in acceleration rate and no accompanying vibration above the norm. No smoke.
This continued for a few miles, in any gear bar top (too fast for these roads) somewhere between 3.75-4k rpm, chirrrrp. On route back it stopped and then I hit traffic the rest of the way so those rpms weren’t appropriate. Riding below these revs accelerating as hard as I like all is normal. This was the 3rd ride in the last week so it’s not been standing, no issues before just suddenly yesterday.

This morning I’ve checked for anything loose, especially header nuts and my recent silencer swap that the clamps were tight, all good. I did wonder if it was somehow a sloppy chain but that’s 25mm on side stand so no.

Very odd but obviously keen to find the cause here before it’s more of an issue
 
Café au Lait said:
Just when I thought I could relax and enjoy the ride…

Okay, so yesterday I decided to brave the cold and enjoy the sun on nice salt free dry roads. 2nd kick and within a mile perfect idle without adjusting the FCR idle speed, perfect.

20 minutes later, 10 miles down range, one of my favourite local roads was clear time to scoot on a bit. Then accelerating half throttle in 3rd at approx 4k rpm and loudish ‘chirrrp’ from underneath me, or at least that’s my perception with custom earplugs with an open face helmet, WTF? Beyond and below 4k nothing. At no point is there any loss of power or any change in acceleration rate and no accompanying vibration above the norm. No smoke.
This continued for a few miles, in any gear bar top (too fast for these roads) somewhere between 3.75-4k rpm, chirrrrp. On route back it stopped and then I hit traffic the rest of the way so those rpms weren’t appropriate. Riding below these revs accelerating as hard as I like all is normal. This was the 3rd ride in the last week so it’s not been standing, no issues before just suddenly yesterday.

This morning I’ve checked for anything loose, especially header nuts and my recent silencer swap that the clamps were tight, all good. I did wonder if it was somehow a sloppy chain but that’s 25mm on side stand so no.

Very odd but obviously keen to find the cause here before it’s more of an issue
Click to expand...
Head gasket leak.

Try retorquing the head.
 
Sadly ‘chirrrrp’ is kinda difficult to translate.

But a chirrrp or squeeele is often omitted by a slipping clutch.

Your rpm could perhaps correspond with max torque, and consequently, max load on the clutch.

Just a thought.
 
Last edited:
Fast Eddie said:
Sadly ‘chirrrrp’ is kinda difficult to translate.

But a chirrrp or squeeele is often omitted by a slipping clutch.
Click to expand...
I’m confident that’s not it. My clutch when warm can chirup/squeel a bit when pulling away from a standstill but there’s no slippage, loss of pull, raised revs etc. No it sounds more metallic than that. Out on the ride pull the clutch and when I got home I revved the engine to 4k in neutral, nothing, all good, only under acceleration. Next time I’m out, I’ll put my phone on the bike and try and record it.
 
With my stock primary case set up, between the clutch plates getting a little fluid on them, and the noisy sound of the primary chain I didn't get a sense of what noise the clutch makes when it engages. (or slips) After I switched to the CNW belt drive, I could hear the clutch plates make this sound that I describe somewhere between a chirp and a squeal. It only really happens when I launch from a stand still because I think my shifts are well timed so the engagement of successive gears happens without much slipping...

I would bet your clutch is slipping. I would imagine you have a hydraulic clutch so I don't know about adjusting that, but the amount of "grab" that your clutch has is determined by the clutch plate stack height. If you replace a thicker plate with a thinner plate (or numerous thinner plates) your clutch will grab much more aggressively... and with the hydraulic clutch, you may not even feel the difference. (but how would I know, I have a clutch cable) The relationship also exists between the plate stack height and how heavy the clutch lever feels and setting the stack height is a compromise to get a balance of solid plate grip when engaged and lightness of lever pull.
 
o0norton0o said:
With my stock primary case set up, between the clutch plates getting a little fluid on them, and the noisy sound of the primary chain I didn't get a sense of what noise the clutch makes when it engages. (or slips) After I switched to the CNW belt drive, I could hear the clutch plates make this sound that I describe somewhere between a chirp and a squeal. It only really happens when I launch from a stand still because I think my shifts are well timed so the engagement of successive gears happens without much slipping...

I would bet your clutch is slipping. I would imagine you have a hydraulic clutch so I don't know about adjusting that, but the amount of "grab" that your clutch has is determined by the clutch plate stack height. If you replace a thicker plate with a thinner plate (or numerous thinner plates) your clutch will grab much more aggressively... and with the hydraulic clutch, you may not even feel the difference. (but how would I know, I have a clutch cable) The relationship also exists between the plate stack height and how heavy the clutch lever feels and setting the stack height is a compromise to get a balance of solid plate grip when engaged and lightness of lever pull.
Click to expand...
Again, I’m used to that sound from my cNw clutch setup, it sounds nothing like that. The bike runs 100% as I’m used to bar this sound at that rpm although it did stop doing it on the return run, 6 miles or so. I’ll take it out when the roads dry again and see if it persists and try and record it.

As Nigel said, it’s hard to translate ‘chirrp’ but this sound is distinctly different and louder frankly but most notably only at that rpm in any gear beyond 4k it pulls as usual, hard but I only went to a little over 5k just in case.
 
This is very unlikely to be your issue, but one of the weirdest problems I've ever fix on a motorcycle was a Triumph T140 with a chirp.

On each exhaust stroke the drive side would chirp like a bird but at first, I didn't know that it was the exhaust stroke. I thought it might be the muffler and swapped them side for side - no change. After listening a lot and trying lots of things I took off the exhaust header and looked inside. The main part of the pipe was too far inside of the flange part. Ground that away and the chirp was gone. Later, on two Commandos I found the same thing!

These all happened at idle and sped up with the engine until about 2k RPM and then stopped. I suppose it's possible only in a narrow RPM range.

If it just happens once in a while, it could be the connection between the exhaust and muffler shifting as it gets hot.
 
Nothing at idle or any rpm when bike is stationary. I had recently my silencer welded as a crack had appeared but no such sound emanated before that or since until yesterday; obviously took me by surprise!

I’ve double checked the clamping of both silencers as I swapped them over to hide the repair (which is 80% perfect anyway) underneath so out of view and again no issues until yesterday so doubt it’s connected.

My initial thought when it first happened was something like the chain rubbing momentarily against the chain case but I can’t see how a specific rpm could fit with that; it only lasts a split second then not again as the revs climb higher but also never on deceleration; so only under load/power.
 

Similar threads

Robert_Norton
Notice About Bring A Trailer Auction, TITLED: 30-Years-Owned 1975 Norton Commando 850
Replies
4
Views
737
mean gene
mean gene
F
  • Locked
A Norton Commando History
Replies
16
Views
6,229
L.A.B.
L.A.B.
Back
Top