Noisy third gear

kerinorton · Sep 5, 2014

When I did up the g/box on my 850 about 4 years ago, I renewed all the bearings and worn bushes. I found the hardening had started to wear off the third gear, so when I asked, I was told if I put a new pair of gears in, they would be the same in a very short time as the gears available here are not up to it.
Any comments on this would be welcome.

BTW, we have just had the second wettest winter on record up here in Northland [ NZ ]. I still haven't been able to really test these 3 LED lamps I have mounted on the 850

ashman · Sep 5, 2014

If the hardening has worn the gear will make a lot more noise and the only way to stop it is to replace it or put up with the noise, anyway you only be in that gear for a short time till you put it in top gear.

Ashley

kerinorton · Sep 5, 2014

That's what I figured. It pissed me off at the time because I prefer a quite box. The whole repair was done because a P O 's stupid repairs.
It it rue though that the newer gears are not up to the job?

toppy · Sep 5, 2014

Second gear seem to wear most for some reason. One thing to consider is as the gears wear the metal particles get carried by the oil (which is not filted) to the other gears bearings etc. of the box so they will wear faster than they might otherwise do. So using worn gears will only accelerate the general wearing of the box an lead to larger repairs in future.

B.Rad · Sep 6, 2014

Gidday Kerinorton. a few comments as u asked.
when u say hard case coming off, what form does this take. it is unlikely that it is just wearing smoothly off. so there will either be pitting or scoring. these are 2 seperate modes of failure with different root causes. it is also unlikely that big chunks of hard case just fall off either. if the overload is that bad the teeth will break. I have not seen much scoring on these boxes, but they pit far too early than they should.

in cases of bad tooth spacing, it is the stress overload that causes pitting.severe overload stress will also cause plastic deformation and this may show as a ledge rising a few thou at about half the tooth height. above this there will be destructive pitting and the hard case will be going.so if pitting is present it is vital to determine if it is initial or macro or destructive pitting. gears can be run reasonably well FOR A WHILE with macro pitting IF IT IS WELL MONITORED. all pitting will lead to failure eventually.

There is only 20 to 30 thou hard case. the case will be 60 rockwell C. u cant file this. the core will be 34/36RC and a file eats this like butter. so carefully apply a file to the tooth contact area and check hardness. if there is no hardness, this will be accompanied by a truly awful tooth shape that says throw me away.

the basic problem of these boxes is tooth design. the teeth are bloody awful. there is a lot that can be done to just fix the profile but u still have the same box. a simple thing thing like a 2 degree change in pressure angle gives huge increase in tooth load capacity. RE TTI boxes. even the old gears, while being well made suffered from the inherent problem of bad teeth for the increased power..

As for Andover Norton gears. they are an example of a well made gear. made of correct grade of steel, heat treated to give the right metal structure and made to reasonable accuracy. case 60/62RC, core 32/34 RC. a good example of a commercial quality vehicle gear. however they still suffer from bloody awful teeth.

when buying gears from anyone, ask lots of questions about metal grades, heat treatment dimensional accuracy.tooth shape modifications can be benificial.this information is not secret and anyone reluctant to provide this has something to hide. good gears are unlikely to come from an amatuer in his shed using a milling machine. or even a hob. This has turned into Gearing 101. I have tried to keep the language simple to infrom some readers who may have an interest in this. it is too easy to drift into technical jargon.

But the maker of any Norton commando gears will still suffer from the inherent bad teeth design, no matter how well the gears are made.and gears are made to a price. a profile ground gear will cost a lot more than a gear finished by machining, but take higher contact stress therefore carrying a bigger load for longer.

over the years, vehicle gear HP has increased considerably. but the gears have not got much bigger. they have got better design and accuracy. nothing magic at all.
Is anyone interested in continuing this subject in a gearbox tooth thread. not the box,thats been done to death, just the teeth design. any other gearcutters out there. have to be.
anyway kerinorton, hope this informs. best wishes Bradley

Hobot · Sep 7, 2014

Even though 2nd gear may show more wear as its the best passing gear and Mt. twistie drag racing gear up to almost 90 mph, its 3rd gear that clutch slips most in and my Peel sheared teeth off both cogs. i'm sold on cryo tempering anything with known or suspected weaknesses and hope for the best. I'd also think about the impregnated dry friction coatings, though expect to replace that after a time too. My sense of the 3rd gear factor is the shafts bowing to cause the few degree mis alignment that spikes weak or shearing load higher. Every drag racer I quized said AMC spills guts out once 100 hp torque approached and exceeded, by ancient Norton components long before our specialty items now available. Its good idea to change new tranny build lube like break in engine oil too. i'm sold on thinnest oil like ATF for protection in lower 3 gears but tired of explaining why its also opinion of Manx racers.

kerinorton · Sep 7, 2014

B.Rad said:
Gidday Kerinorton. a few comments as u asked.
when u say hard case coming off, what form does this take. it is unlikely that it is just wearing smoothly off. so there will either be pitting or scoring. these are 2 seperate modes of failure with different root causes. it is also unlikely that big chunks of hard case just fall off either. if the overload is that bad the teeth will break. I have not seen much scoring on these boxes, but they pit far too early than they should.

in cases of bad tooth spacing, it is the stress overload that causes pitting.severe overload stress will also cause plastic deformation and this may show as a ledge rising a few thou at about half the tooth height. above this there will be destructive pitting and the hard case will be going.so if pitting is present it is vital to determine if it is initial or macro or destructive pitting. gears can be run reasonably well FOR A WHILE with macro pitting IF IT IS WELL MONITORED. all pitting will lead to failure eventually.

There is only 20 to 30 thou hard case. the case will be 60 rockwell C. u cant file this. the core will be 34/36RC and a file eats this like butter. so carefully apply a file to the tooth contact area and check hardness. if there is no hardness, this will be accompanied by a truly awful tooth shape that says throw me away.

the basic problem of these boxes is tooth design. the teeth are bloody awful. there is a lot that can be done to just fix the profile but u still have the same box. a simple thing thing like a 2 degree change in pressure angle gives huge increase in tooth load capacity. RE TTI boxes. even the old gears, while being well made suffered from the inherent problem of bad teeth for the increased power..

As for Andover Norton gears. they are an example of a well made gear. made of correct grade of steel, heat treated to give the right metal structure and made to reasonable accuracy. case 60/62RC, core 32/34 RC. a good example of a commercial quality vehicle gear. however they still suffer from bloody awful teeth.

when buying gears from anyone, ask lots of questions about metal grades, heat treatment dimensional accuracy.tooth shape modifications can be benificial.this information is not secret and anyone reluctant to provide this has something to hide. good gears are unlikely to come from an amatuer in his shed using a milling machine. or even a hob. This has turned into Gearing 101. I have tried to keep the language simple to infrom some readers who may have an interest in this. it is too easy to drift into technical jargon.

But the maker of any Norton commando gears will still suffer from the inherent bad teeth design, no matter how well the gears are made.and gears are made to a price. a profile ground gear will cost a lot more than a gear finished by machining, but take higher contact stress therefore carrying a bigger load for longer.

over the years, vehicle gear HP has increased considerably. but the gears have not got much bigger. they have got better design and accuracy. nothing magic at all.
Is anyone interested in continuing this subject in a gearbox tooth thread. not the box,thats been done to death, just the teeth design. any other gearcutters out there. have to be.
anyway kerinorton, hope this informs. best wishes Bradley

Yes please do keep this thread going. I agree with you. Straight cut teeth are dinosaurs but still used on earlier gearboxes on first gear, where they lost the hardening off the middle or their trust faces. When I was told the new gears would wear their hardening of after a short time, and that my existing gear would probably be ok, I reused them. Still, it is an easy job to change them. I think you implied that Andover may have had the best gears??????. I am going to have to change them soon so am keen to know which ones are the better ones.

Another question, do you know what causes the kick starter to rotate backwards under harder acceleration. Someone told me it was because of a worn bush in the kick shaft, another said it probably was a bent shaft. When I rebuilt the gearbox, I replaced all worn bushes, but the kick starter bush did not appear worn enough to replace.
regards, Dereck

kerinorton · Sep 7, 2014

hobot said:
Even though 2nd gear may show more wear as its the best passing gear and Mt. twistie drag racing gear up to almost 90 mph, its 3rd gear that clutch slips most in and my Peel sheared teeth off both cogs. i'm sold on cryo tempering anything with known or suspected weaknesses and hope for the best. I'd also think about the impregnated dry friction coatings, though expect to replace that after a time too. My sense of the 3rd gear factor is the shafts bowing to cause the few degree mis alignment that spikes weak or shearing load higher. Every drag racer I quized said AMC spills guts out once 100 hp torque approached and exceeded, by ancient Norton components long before our specialty items now available. Its good idea to change new tranny build lube like break in engine oil too. i'm sold on thinnest oil like ATF for protection in lower 3 gears but tired of explaining why its also opinion of Manx racers.

As it is the gears I am more concerned about, I still use 90 gear oil, plus I have added slick 50 as well. ATF is good in manual gearboxes, but is it suitable in boxes with straight cut gears. Most g/boxes that specify ATF are full synchro and diagonal cut gears [ bugger I have forgotten the name for them now ]

toppy · Sep 7, 2014

Another question, do you know what causes the kick starter to rotate backwards under harder acceleration. Someone told me it was because of a worn bush in the kick shaft, another said it probably was a bent shaft. When I rebuilt the gearbox, I replaced all worn bushes, but the kick starter bush did not appear worn enough to replace.
regards, Dereck

Kickstart moving under acceleration is normaly quoted by many as a sign of failing layshaft bearing. This is something you should address ASAP plenty of posts on the subject elsewhere on thìs forum.

As for AFT many modern gearboxes still use EP 90 or 85 and some manual boxes using it have built in oil pumps to feed it constantly where needed an not rely on splash lubrication. If i had just paid out big money on a TTI box Hobot i would put in the oil they told me to. They made it so they must have allowed for the use of a certain type and grade of lubricant.

Hobot · Sep 7, 2014

Yep if only the gear faces were the main wear issue then thick gear lube is better. If kicking up rpm heels mainly in lower gears then its the sleeve bushes that wear d/t lack of heat removing lube flow which lets shafts wobble which misalign gear meshing which removes their surface faster. I run gear lube in my factory Combat but avoid much lower gear use and would have no quams to use ATF if no gear lube left. Those long before me proved ATF worked a treat in AMC's and Peel's testes verified it for me too.

kerinorton · Sep 7, 2014

Hi Bradley. When I rebuilt the gearbox, I fitted new bearings, and the inner layshaft bearing is a superblend type. Hopefully that is still ok as it has probably done less the 10,00 since the rebuild. Is it that bearing you are referring to or the bush in the kick start shaft. The keck starter lever reaction starter fairly soon after my rebuild, and I think it may have been noticeable on occasions before hand. Mostly only in 3rd gear I think.
BTW what part of Queensland are you living in.

Steve, most of my travelling is at the higher speeds, and although I do run 1st and second on the sharp bends round here, is isn't often at high power as the roads are not that good so you have to be a bit wary of cranking the turps or you may end up pretending to be a plow. Mind you, I have been over the side on more than one occasion, but been lucky enough to "plow" up the side again and back on to the road using the wheels alone. Great fun and certainly gets the blood flowing, and leaves a funny taste in your mouth. [ with the S.F.I. conversation going on in my head.]

Hobot · Sep 8, 2014

Steve, most of my travelling is at the higher speeds, and although I do run 1st and second on the sharp bends round here, is isn't often at high power as the roads are not that good so you have to be a bit wary of cranking the turps or you may end up pretending to be a plow. Mind you, I have been over the side on more than one occasion, but been lucky enough to "plow" up the side again and back on to the road using the wheels alone. Great fun and certainly gets the blood flowing, and leaves a funny taste in your mouth. [ with the S.F.I. conversation going on in my head.]

Ugh that's not unlike my own home run offs and I hate that taste of stress hormones. I do not barn storm in lower gears on ordinary un-multi linked Commandos, so any lube works for that. It don't take hi power in lower gears, just time engaged to dry em out though more power/rpm wears em out faster. If mostly shifting to get into 4th then there's time for the thick lube to weep from above into the non spinning sleeve bush spaces plus time to cool down cooking what little oil remains not already slung out. When I ride faster than needed I'm in very alert control & never a close call, so its only the out of the blue drifters and animals causing my off my road saves or less damaging crashes. Getting run off into drainage slopes and back to road grade is a superior feat of fighting spirit and skill to me. Hope you figure out the kicker catching, as mostly its the well known lay shaft bearing danger so must find out if yours is failing too soon or some other hang up listed.

B.Rad · Dec 25, 2014

kerinorton said:
B.Rad said:

Gidday Kerinorton. a few comments as u asked.
As for Andover Norton gears. they are an example of a well made gear. made of correct grade of steel, heat treated to give the right metal structure and made to reasonable accuracy. case 60/62RC, core 32/34 RC. a good example of a commercial quality vehicle gear. however they still suffer from bloody awful teeth.

Yes please do keep this thread going. I agree with you. Straight cut teeth are dinosaurs but still used on earlier gearboxes on first gear, where they lost the hardening off the middle or their trust faces. When I was told the new gears would wear their hardening of after a short time, and that my existing gear would probably be ok, I reused them. Still, it is an easy job to change them. I think you implied that Andover may have had the best gears??????. I am going to have to change them soon so am keen to know which ones are the better ones.

Click to expand...

Gidday Kerinorton. been a while but here is more info. Your use of the term "best gears" needs clarifying. to be classed best would imply the set would take more power for a longer time than other sets available or even be capable of taking more power than is available, ie, overbuilt. however there is a direct relationship between accuracy and cost, and the "best" set may be way too expensive. So any further comments are directed at the box fitted to Commandos.

gears are made in different classes. we need to concern ourselves with vehicle gears about AGMA quality no 9/10. these are unground teeth used as heat treated. there is no mystery to vehicle gear practice at all. google will reveal all.

whoever advised you that the hard case will fall off or wear quickly is dead wrong. if it does it is a truly rubbish gear.
Andover gears are a good example of a well made gear. andover does not make these gears. good gears are made by specialist gear companies. but they still suffer from poor teeth design. andover gears are of known quality.

Lubrication. hot thin oils cause more damage than hot thick oils when the set is highly loaded. Please check this for yourself, the contrary view is myth. use EP additive too. get rid of the Slick 50. Use reputable oils. all the basic stuff her.

Durability. of course any used gear set will show some signs of wear. the trick is to know when to chuck away. even what may seem severe pitting may still have reasonable life left.BUT THIS MUST BE MONITORED. and measured. if the hard facing is completly gone, that means the teeth will be a 1/16th" thinner. they will break before this .

Bad Teeth: Mate I have a little drawing of the 1st gear inbuilt design problem. I am having trouble posting this. Could you PM me your email and perhaps be kind enough to post this here for me please. The drawing is self explanatory. you will clearly see the difference. also my previous post gives you the specs of a very suitable gears to use in your commando.

A query?. how many people are making or what is the availability of non standard gears either using standard numbers of teeth and modified tooth dimensions, or non standard numbers of teeth entirely, ie, different ratios.. Also for 4 speed only. I have no idea what is available.
Best wishes Aussie Bradley

kerinorton · Dec 25, 2014

Hi Bradley. I am using 80-90 gear oil with the slick 50 additive which is supposed to put a Teflon coating on all the metals. I ADDED THE SLICK 50 HOPING IT WOULD HELP THE GEARS TO LAST LONGER. uNFPORTUNATELY, THEY WERE NOISER AFTER THE REBUILD.
dERECK

CHEK PM.

comnoz · Dec 25, 2014

Over 100,000 miles on my gearbox now. At least the last 80,000 have been with ATF for lube. And yeah it's a bit noisy.

ATF is used in over the road diesel automatics and they use straight cut gears.
A straight cut gear can handle a larger load if noise is not a concern. Jim

kerinorton · Dec 26, 2014

so what do I do. just keep riding and use third gear only when necessary. I do favour getting to top and quick as possible, even using it through towns at 30 mph. My gearbox oil has always been 20mm higher than the level recommended. [ don't have problems with the clutch because it gets washed regularly as a result of the leaking engine main seal. and oil is cheap compared to the time to change that bloody seal ] The 3rd gear fair screams without a load on it.
Dereck

toppy · Dec 26, 2014

kerinorton said:
so what do I do. .
Dereck

Your own posts end with..
if it ant broke dont fix it

Well that answers your own question. It is not ment to make that noise so its broke.

Noisy third gear

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