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.

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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.

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they should be rubber mounted to the Z plates as standard.

jan nelder said:

they should be rubber mounted to the Z plates as standard.

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Matt’s earlier builds used fancy coil springs but found them troublesome I believe so yes, mounted with rubbers on the Zs.

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

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Head gasket leak.

Try retorquing the head.

I will certainly check that, thank you. FWIW, no leaks though.

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.

Fast Eddie said:

Sadly ‘chirrrrp’ is kinda difficult to translate.

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

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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.

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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.

Sheet metal vibration?

on reflection, somewhere between chirrrp and graunch

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.

Maybe the tube inside the ’repaired’ muffler is cracked, and ressonates at a certain rpm.

ludwig said:

Maybe the tube inside the ’repaired’ muffler is cracked, and ressonates at a certain rpm.

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Worth I look but wouldn’t resonate at that rpm when parked up or on deceleration?

It appears I’ve finally got to the bottom of the ‘odd noise’ issue on my bike. Fingers crossed. Turns out it’s what I initially suspected, the chain!

This chain is the original D.I.D. 520VX2 from the build back in 2013 and some 12.5k miles but only 2.5k since Matt replaced the swing arm before being shipped. Never ridden in the wet, always dried after a wash and immediately lubued.

Looking really closely I wiped away some lube build up from the forward chain guard lug and saw this:


This being a brand new swing arm it’s clear the chain has been making contact. To test this I applied Tipex and went for a ride. Yep, when I heard the noise I dismounted and the Tipex had been partially removed, bingo. I also Tipexed the Master Link tips and they were getting rubbed too, on the inner primary case I found by crawling under the bike with a torch.

Removing the chain revealed that although it had only stretched less than 1mm its ability to flex sideways was more that 1cm at the ends and worse of all, 3 links were seized and 5 others were fairly tight, totally bolloxed in other words.

Yesterday I replaced with a new VX3 but decided to rivet this time as I found that the Master Link pins on the new one were slightly longer than the old and that they immediately fouled the chain guard.

Last nights 30 mile ride went brilliantly until the very last mile when a small recourance of the noise happened but new Tipex was unmarked. I realigned the wheel and corrected a slightly too tight chain and no all seems well, fingers crossed. Regardless, I’m pretty confident this was the issue all along and any return if most infrequent at least suggests nothing nasty is lurking. But then again…

The saga continues. Despite all my efforts and emails with Matt the noise is still intermittently present.

I classic bike builder neighbour over a beer immediately thought it sounded like a misfire from my description, running a bit rich. With that in mind I set to by checking my service notes and when I’d replaced the worn needles I retained my previous adjustment of lowest clip position. I thus put it back to spec, 2nd from bottom and the test ride went very well until, again towards the end and it did it!

Still like the chain replacement (shiny new chain with no seized links) there is an upside, 62mpg up from 55 even with all that throttle testing action.

Yesterday I thought back to what changes I’d performed since this noise showed in mid February and the last was the exhaust repair which for cosmetic reasons to hide the welding I swapped the silencers so swapped them back. Again, the test ride seemed like I’d found the culprit but alas towards the end of my ride, bugger.

So effectively I’m back to square one. A bike the performs as well as ever but sometimes makes a bloody odd noise @ 3/4 throttle or above between 3-4rpm which I’m convinced emits from the right silencer.

Matt agrees with me, I need a pair of Commando experienced ears on this one. I’ve a NOC rally in France coming up mid June and I’m in need of some reassurance or remedy by then if I can.

Café au Lait said:

The saga continues. Despite all my efforts and emails with Matt the noise is still intermittently present.

I classic bike builder neighbour over a beer immediately thought it sounded like a misfire from my description, running a bit rich. With that in mind I set to by checking my service notes and when I’d replaced the worn needles I retained my previous adjustment of lowest clip position. I thus put it back to spec, 2nd from bottom and the test ride went very well until, again towards the end and it did it!

Still like the chain replacement (shiny new chain with no seized links) there is an upside, 62mpg up from 55 even with all that throttle testing action.

Yesterday I thought back to what changes I’d performed since this noise showed in mid February and the last was the exhaust repair which for cosmetic reasons to hide the welding I swapped the silencers so swapped them back. Again, the test ride seemed like I’d found the culprit but alas towards the end of my ride, bugger.

So effectively I’m back to square one. A bike the performs as well as ever but sometimes makes a bloody odd noise @ 3/4 throttle or above between 3-4rpm which I’m convinced emits from the right silencer.

Matt agrees with me, I need a pair of Commando experienced ears on this one. I’ve a NOC rally in France coming up mid June and I’m in need of some reassurance or remedy by then if I can.

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Let’s try for a meet at the H this weekend shall we ?

However, if I come on the 961 I will most likely not even be able to hear your tiny intermittent noise above the clatter and clanging of mine !

I do have an initial diagnosis for you though… don’t ride below 4k rpm… duh…