IT MIGHT BE OUT IN LA LA LAND BUT HERE GOES!

While I am rebuilding and inspecting my gearbox… gears, bushings, bearings… I find most gears have some pitting at the pressure point areas where the corresponding mate runs. I just wanted to get the 2nd gear upgrade for my 72 Combat which bring the gear closer to 3rd (the ones with the Groove markings) but after I did a thorough cleaning with my ultrasonic tub and then inspecting all the gears carefully they all seem to show Brinelling. Going to a belt drive system will alleviate this I hope. I will end up replacing the entire set with new. But here is my question. Has anyone tried using cryogenic metal treatment to his or her commando parts? Am I way over the top or is this affordable and worthwhile. I know this is done in racecars and industry. Your thoughts on this if you have used this treatment.???
CNN :?:

You better have deep pockets as this can be VERY expensive, I have never done it but know people that have. Never heard of doing gears though. Good luck, Chuck.

take a look at http://www.diversifiedcryogenics.com/index-2.html they seem to do just about anything and decent prices.

they are pretty well known as http://www.frozenrotors.com and they're right here in MN!

Brinelling?

Hi I think maybe when talking about gears you will find pitting and the severe form called spalling. Lack of lubrication is 1 cause and misalignment another which together can cause higher working temperatures which can cause damage. However you can have some pitting on your gears which has occured from many years of use and although present does not mean they will explode or anything of the sort. The most important wear to look for is on the teeth is it more than pits or has spalling taken place with lines and cracks and obvious weardown. This would most likely lead to failure of gear and other components. Pitting itself does not mean the gear is no good. Hope this helps .. Doxford 69 750 roadster

pitted gear teeth

I have not seen a Commando gearbox that didn't have pitting on the gear faces. I don't believe the AMC box wasn't intended for the engine output a Commando delivers. Gear teeth failures are still pretty rare and usually due to youthfull abuse.

You should see how pristine the gears are on my '61 ES2.

David

Hi David,

You have an ES2? I'm green with envy! Can you post a photo or two? Would love to see them.

Back on topic, my gears had some light brinnelling but I didn't worry about it. On the 850's gearbox I had a couple of gears with worn dogs so those got replaced but the gear teeth all looked pretty good. The kickstart shaft was cracked though, and the mainshaft was bent. The 750's gearbox was actually in pretty good shape.

Debby

As illf8ed mentioned, the AMC gearbox is overstressed when used with the Commando engine. Going to a belt drive is an interesting solution, but I doubt that it will prevent the pits you describe in the gears. I believe the pits are the result of excessive contact stresses between gears, or spalling as I call it. Chances are the belt will not reduce those stresses sufficiently to prevent spalling. I don't have a good understanding of cryogenic metal treatment, but it sounds cold and brittle!

Also as mentioned, all Commando gearboxes will show spalling to some degree, and all out failures are rare. It’s just another Commando quirk that you must learn to tolerate.

There was once someone who said those little imperfections in some of your parts are not bad at all, In fact they tend to hold oil and that is good! LOL LOL :lol:

An ideal tooth form would be a geometrically perfect shape with an ultra-fine rms finish (mirror gloss) except for a 2% pattern of oil retention channels (similar to a good "plateau" cylinder wall hone).

I quite agree with the posters who have said that this is inevitable. When I first rebuilt my Commando, I replaced all the gearbox internals. A couple of years later, the drain plug thread pulled out (I think that I wore it out with paranoid 1000 mile oil changes actually :shock: ) The gears showed spalling once again so eight new pinions and a set of bushes and back together again.

10,000 miles on, a precautionary check showed the same wear pattern as the gears that I removed. Around this time, I made a huge philosophical leap and concluded that it is just not possible to keep a Commando's internals looking perfect in combination with hard use.

The good news is that after the initial degradation, they only wear very slowly and some of the worst ridging which the teeth have from new has usually polished off as well.

In my experience, the box will whine in second and third if it's really badly worn but even then, it doesn't mean that catastrophic failure is imminent. If a box wasn't whining and has not gone through the hardening across the full width of the teeth, my policy would be simply to rebush and reassemble.

I put a 'Dolls Head' box back together with new bearings at the weekend and the gears are virtually identical with the Commando. Not surprisingly, the teeth were perfect but on the 16H they only have to cope with 12BHP

I didn't cryo treat my gears (I did do my crank and case halves, also shot peened and deburred the inside of the case halves), but I did have them coated with a dry film lubricant coating. All were moderately priced.

I have no comparative data, but I've used these processes in other engines and have never been displeased with the results. That said, there could be no benefit whatsoever.

I had these folks http://www.performancecoatings.com/index2.html coat everything with every coating they recommended. So far so good.

Dave
What did it cost to do your crank and cases??
I was thinking of using Molybdenum disulfide to treat the gears before assembly.
Putting them in a tumbler with small steel shot to treat the gear set steel at a molecular level. The bench rest shooters use this process on bullets to help in barrel wear and increases velocity to the bullet.
I have read in other forums that the triple chain and bronze friction plates created a vibration to the gears chattering back and forth which causes the pitting in the gears. In other words there is too much of a flywheel at the clutch basket. By going to a belt drive system and back to Surflex fiber friction plates I am in turn lightening up the flywheel effect at the box.
Regards,
CNN

Dave / Canuk...,

I assume you guys are concerned about a crack initiating from inside the crankcase - hence the shot peening. I've not heard of a Norton engine case developing a crack; please share your experiences.

Sorry for the delay.

I did the cases because I've seen a handful on the floors of various garages that had some ugly cracks. Most emanated from (or terminated at) the bearing area. Keith Johnson also said he's seen some pretty porous castings and it would help keep mine from weeping oil if it was. (Some folks paint the inside of the cases to prevent the same condition.)

Cost for the crank and case halves - with the shotpeening - was like $230 USD in the fall of 2006. Smallish shop in Edmonds or Lynnwood - I'll look for the receipt in my pile. The company works largely with turbine blades and aircraft propellers, so I figured they might have an idea what they were doing. 8)