cNw #101 Norton Commando 850

concours said:
Yes.

There is a saying, about Commando: "a 30hp transmission mounted behind a 60hp engine"

It pokes fun at the evolution of things.

Very awesome of Matt to have acted upon a subtle whisper heard by a trained ear.
A solid move.
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Obviously I asked Matt his thoughts;

“Its of course hard to say exactly what happened but I think its because of a weak gear. In other words, a gear that was not as strong as it needed to be and it just broke off. I say this because of the clean break and if it was due to a load, more teeth would have sheared. I have seen this gears missing 3 or 4 teeth when taking gear boxes down.

Also, teeth broken due to running the bike hard is typically happening in first or second gears. In 4th, you are already at speed and not accelerating much any longer.”

I wonder, purely as a layman, that ‘using all the torque available’ in top would have put undue stress upon the box?
 
On a more positive note. It looks like I have a shipping date. End of March or 1st week of April. Naturally the choice is down to Matt be fully happy with the bike; his shipper can do either. This could potentially be a stressful time but I’m determined to chill and take things as they come. Hopefully all will be plain sailing and I’ll get to ride in the forthcoming 6-8 weeks.
 
Café au Lait said:
Obviously I asked Matt his thoughts;

“Its of course hard to say exactly what happened but I think its because of a weak gear. In other words, a gear that was not as strong as it needed to be and it just broke off. I say this because of the clean break and if it was due to a load, more teeth would have sheared. I have seen this gears missing 3 or 4 teeth when taking gear boxes down.

Also, teeth broken due to running the bike hard is typically happening in first or second gears. In 4th, you are already at speed and not accelerating much any longer.”

I wonder, purely as a layman, that ‘using all the torque available’ in top would have put undue stress upon the box?
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Matt is spot-on, as usual.🏁

First, understand torque multiplication theory of a transmission.💡


As for practical application of said theory, I run my 850 WFO for sometimes 20-30 miles in top gear. 🏁💨
 
Café au Lait said:
On a more positive note. It looks like I have a shipping date. End of March or 1st week of April. Naturally the choice is down to Matt be fully happy with the bike; his shipper can do either. This could potentially be a stressful time but I’m determined to chill and take things as they come. Hopefully all will be plain sailing and I’ll get to ride in the forthcoming 6-8 weeks.
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Lookin’ forward to meeting up at the H !
 
Fast Eddie said:
Lookin’ forward to meeting up at the H !
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Yeah me too, thanks. The Six Bells at Warborough is probably more appropriate for these machines though don’t you think?

I’ve not spoken about my new sled to my mates, thought I’d just pitch up on a yellow cNw and blow their minds:eek:

Thanks to all here for your kind support.
 
Hey guys,

From a sunny and warm, then snowy and cold and some hail to top it off, Dolores Colorado (7K feet), in other words typical early spring weather in the Rockies.

The broken gear in #101 was certainly a bit of a surprise. Having taken down and built a few hundred of these gear boxes, I have seen quite a few broken gears, so not necessarily something that could never happen.

Sure, there is plenty of torque applied in 4th but a rapid shift (little or no clutch use) in a low gear would apply more shock and that could break a gear. If the sleeve gear bushings were all worn down so that there was a sideways load on the gear could also cause problems but the bushings in #101 are still really nice and tight so the gears are running true.

Of course, I don't know when it may have happened. Could have been miles ago or recently. Probably recently since the gear box oil really moves around in there and if that tooth would have been tossed in the mix, I think I would have found more problems. Bottom line, other than the broken gear and some relatively sharp edges on the sleeve gear, everything else internally looked very nice.

Maybe someone with a better understand on metallurgy could look at the surface where the tooth broke off and determine if it is as intended or maybe a weak or compromised area.

Chinese parts. I am trying my best to never use anything made in China. That said, quality and my customers come first and if there is a part that is of a high quality and it happens to be made in China, I have and is still using some. The main shaft bearing is the only Chinese bearing used on a cNw build. I have never seen one fail or at least never been made aware that one did in case it happened. If that was the case, I would have promptly sourced something different. I have been working with a bearing house for 20+ years that helps me find high spec bearings that are stronger than the originals and often by a big margin. Not an area where I think cost should be a determining factor.

Oil changes. My recommendation for frequent oil changes is one that I have pushed for years (1,000-1,500 miles). Air cooled engines are hard on oil and while what type of oil could be argued until the end of time, I don't think anyone disagrees that dirty oil is bad. Doing oil change on a Commando is relatively inexpensive, easily and quickly done and one thing that can ensure that the internal parts, bushings and and bearings are treated with clean lubrication. It can also show that something bad is going on inside, like a lot of metal traces or even bits and pieces, and you can catch it before it gets really ugly....

Cheers to all......back to wrenching !

Matt
 

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<My recommendation for frequent oil changes is one that I have pushed for years (1,000-1,500 miles)>

I started doing that 50 years ago and have often been told Im wasting my money. But I worked for an
old racer who said the oil should never get dirty on a brit bike. The oil is compromised by an air cooled
engine and the various substances that come from wear should be removed. Maybe it is over the top
but how much did your overhaul cost and how much is oil? Even in the UK where oil is not cheap it is still
a cost effective move. IMO.
 
Looking at the chicom main bearing pix, it appears to me Matt installs a 2RS
bearing. Wondering if it is better to pull the inner rubber seal or not.
Comments?
 
Onder said:
<My recommendation for frequent oil changes is one that I have pushed for years (1,000-1,500 miles)>

I started doing that 50 years ago and have often been told Im wasting my money. But I worked for an
old racer who said the oil should never get dirty on a brit bike. The oil is compromised by an air cooled
engine and the various substances that come from wear should be removed. Maybe it is over the top
but how much did your overhaul cost and how much is oil? Even in the UK where oil is not cheap it is still
a cost effective move. IMO.
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Considering the bikes cost it’s nothing to change the oil more regularly but my query had nothing to do with cost anyway, just curiosity over why; I’m naturally totally confident with all of Matt’s recommendations a big part of the decision believe me.
 
Café au Lait said:
Considering the bikes cost it’s nothing to change the oil more regularly but my query had nothing to do with cost anyway, just curiosity over why; I’m naturally totally confident with all of Matt’s recommendations a big part of the decision believe me.
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Basically, these old engines allow more blow-by than modern engines, thus they suffer increased oil pollution.

But worse, they run hot, especially the cylinder head on a Norton, thus they really give the oil a hard time temperature wise (amongst other things, this breaks down the viscosity of the oil).

So, in summary, old Brit bikes pollute and cook the oil. Thus more frequent changes make good sense.

Case study: I had a BSA R3 track bike once that cooked its oil in less than one weekend, to the extent the oil light came on! And that was using top drawer Silkoline comp synthetic too.

Simon, find the oil test thread done by Comnoz in order to choose your oil.
 
My take is it is extra important to do the low milage oil changes on a bike with the K&N conical filters on the back of Keihin FCRs as is the case with the cNw bikes. Also important to clean and re-oil those K&N filters on a street bike.

I don't use a Comnoz recommended engine oil or a motorcycle oil, I use Lucas high zinc hot rod oil, but I change both the engine oil and gearbox oil frequently. Never a puff of smoke out of my engine. AMC gearbox is another story. One too many rides home in my youth with a busted clutch cable is hard on a gearbox. I'm lucky it still shifts at all. It has been apart, no broken gears, but a finicky shifting box. Not looking for gearbox advice. I'm replacing it.
 
Fast Eddie said:
Basically, these old engines allow more blow-by than modern engines, thus they suffer increased oil pollution.

But worse, they run hot, especially the cylinder head on a Norton, thus they really give the oil a hard time temperature wise (amongst other things, this breaks down the viscosity of the oil).

So, in summary, old Brit bikes pollute and cook the oil. Thus more frequent changes make good sense.

Case study: I had a BSA R3 track bike once that cooked its oil in less than one weekend, to the extent the oil light came on! And that was using top drawer Silkoline comp synthetic too.

Simon, find the oil test thread done by Comnoz in order to choose your oil.
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Thanks but I thought I’d start with Matt’s recommendation, seems logical. I do understand he’s at 7k ft though
 
TAKE COVER!!! Threat of derailment to another Oil thread risk!!

I did read the article under ‘Technical’ last week (if that is what is being referred to) and it seemed to me, for road bike use, Mobile 1 and Royal Purple HPS were solid choices. Regardless I’ll defer to Matt in the first instance.
 
gear breakage: that Fourth gear pair are used in 1st, 2nd and 3rd gears, but not in fourth, interestingly.
 
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