Cracking between the bearings

Hello everyone,

Does anyone know if a gearbox with a hairline crack between the main bearing and layshaft bearing can be successfully welded and machined back to service? The alternatives are: A) leave it alone and hope the bearings support the fracture. Or, B) suck up and buy a new shell.

Thanks for the input

Kevin

Just leave it alone. Many gearbox shells have the little hairline crack between the 2 driveside bearings . It's no big deal unless you race , perfectly fine for the road. There are bigger things to address such as fitting a better layshaft bearing as number one.

Torontonian said:

Just leave it alone. Many gearbox shells have the little hairline crack between the 2 driveside bearings . It's no big deal unless you race , perfectly fine for the road. There are bigger things to address such as fitting a better layshaft bearing as number one.

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+1
I chose to leave mine as is, logged 20,000 miles since. Looks the same

Crack is not to worry as long as sleeve gear bearing stays in its place axially.
If not, fix it.
Can be done without welding.
Basically same process as for fixating crankshaft bearing outer ring in crankcase by washer-and-screw method.

The issue has been discussed in the past. Check out this link:
gearbox-crack-t6787-30.html

Stephen Hill

I ultimately took the shell to my local shop and had them press the bearings in. They used a little red lock tight for a little extra insurance. Now I can get back to the business of putting my gearbox together. Thanks everyone for the advice!

Kevin

FreeRadical said:

I ultimately took the shell to my local shop and had them press the bearings in. They used a little red lock tight for a little extra insurance. Now I can get back to the business of putting my gearbox together. Thanks everyone for the advice!

Kevin

Click to expand...

Did you heat it before fitting bearings?

Yes, the shop tells me they heated the case and put the bearings in the freezer. Using a set of graduated drifts, they tapped them in. They claim they went in easy.

Now that I have the gearbox together again, I have almost no endplay. Should I start second-guessing the bearing install? How can I verify if the bearing has been driven all the way home? Are there other areas within the gearbox that I can check that might account for no end play?

Thanks again,

Kevin

Re: Cracking between the bearings - HELP

Here is a picture from the primary side. If you notice, you can see into the bearing past the oil seal. I'm guessing there should NOT be a gap there. Meaning the bearing is not seated all the way???

Re: Cracking between the bearings - HELP

Looks normal. The seal runs on the gearbox sprocket spacer.

Re: Cracking between the bearings - HELP

OK. So assuming the bearings are installed properly, is there anything else than can effect end-play?

Below is a picture of the inner race of the roller bearing. It was very tight going on to the layshaft. Using a dead blow, I "tapped" on the opposite end of the shaft and convinced it onto the shaft. The race is currently FLUSH with the end of the shaft (the picture shows a little less than flush. I "tapped on it a little more after the photo). Maybe I tapped a little too much?

Re: Cracking between the bearings - HELP

FreeRadical said:

Using a dead blow, I "tapped" on the opposite end of the shaft and convinced it onto the shaft. The race is currently FLUSH with the end of the shaft (the picture shows a little less than flush. I "tapped on it a little more after the photo). Maybe I tapped a little too much?

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I think perhaps you are being a little overcautious? If there's insufficient end play-as it is, then the race can't be far enough onto the shaft if it's not up against the shoulder of the gear.

Re: Cracking between the bearings - HELP

I think that inner race needs to be all the way home on the shaft and any free play made up on the other end.

Your 4th gear lay is looking a bit ragged from the pictures point of view.

Re: Cracking between the bearings - HELP

Check everything... kicker shaft bush is fully seated,I had burrs in the four holes the dogs catch in on 1st lay gear. Not burrs from shifting, but burrs from drilling, never deburred. When using the roller lay bearing, the kicker shaft and other parts are called upon to do things were not designed to. It works, but benign defects may suddenly become an issue.

Re: Cracking between the bearings - HELP

FreeRadical said:

OK. So assuming the bearings are installed properly, is there anything else than can effect end-play?

Below is a picture of the inner race of the roller bearing. It was very tight going on to the layshaft. Using a dead blow, I "tapped" on the opposite end of the shaft and convinced it onto the shaft. The race is currently FLUSH with the end of the shaft (the picture shows a little less than flush. I "tapped on it a little more after the photo). Maybe I tapped a little too much?

Click to expand...

FR
It looks like the inner race needs to come down a bit more on the shaft. In you previous picture, don't forget the seal counter-shaft sprocket spacer. If it has a groove from the old seal then I would get a new one. It will keep the oil in better.
Cheers,
Thomas
CNN

Re: Cracking between the bearings - HELP

The shaft should end up a bit proud of bearing or you end up with binding by seating on proud bearing. As mentioned the crack is so so common yet its so so rare for it to cause issues just run it. I shopped around for AMC shells world wide a decade ago and learned that every vendor of much fame and piles of AMC boxes with big bearing bores too wallowed out to hold and not worth expense and risk trying to restore them they wait till alu prices goes up for scrap. $450 was cheapest I found for an intack Commando box. I also learned that Atlas shells were fairly plentiful and IDENTICAL to all Commandos BUT lacks the notch the thick upper DS washer-spacer WHICH I found made Atlas shells rather easier to fit and remove and only cost about half as much as the notched version. I ran Peel most her life with Atlas box after wallowing out the original bores and busting through the main bearing seat so bearing when right through - showing its seat is only ~1/8 thick. Remarkably no crack between bores. I have a spare Qualfe box Ken Canaga restored before I knew I could get TTI gearbox for Peel.

Re: Cracking between the bearings - HELP

Thanks for all the help. I heated the race up and gave her a few more bangs with a spare bearing and dead blow. Worked like a charm and now I have .05" of end play with no shimming (hmmm...). Perhaps the bearings in the shell are standing a tad-bit proud, but I'm going to run with it since they've been red lock-tighted in.

Kevin

Re: Cracking between the bearings - HELP

FreeRadical said:

Thanks for all the help. I heated the race up and gave her a few more bangs with a spare bearing and dead blow. Worked like a charm and now I have .05" of end play with no shimming (hmmm...). Perhaps the bearings in the shell are standing a tad-bit proud, but I'm going to run with it since they've been red lock-tighted in.

Kevin

Click to expand...

I had 33 thou of end play when i rebuilt my box so instead of shims i did not fit the inner cover to gearbox shell gasket. That reduced the end play to 8 thou, I checked the mating faces were smooth an used Wellseal on assembly. Box works fine and no leaks.

A friend has an Engineering business part of which is repairing / rebuilding Nortons that many and so called experts and customers who know little or nothing about Engineering have successfully, to put it politely, buggered up. He makes a reasonable living out of it even though he charges his customers a LOT less per hour than some so called Norton experts I can think of.
I phoned him asking for his thoughts. He stated that he would happily use such a gearbox shell on anything up to 650 cc but would NOT use it on larger capacity lumps as he considered it could lead to premature failure and a riders safety was far more important than the cost of a new gearbox shell.
I do not suppose many reading this will be aware of the history of the gearbox......My old Wakefield Oils book 'Gear Lubrication' in the motor cycle section shows (page 106) the 28t - 18t 4th gear pair as fitted to the earlier Burman gearbox which was I SUSPECT designed in the 1930s. The ONLY difference between the gears shown and those in my ES2 so called AMC/Norton box is that to cheapen things they removed the roller bearings one end of the 28t sleeve gear simply extending the bush. The book states and I quote ' The box is guaranteed for 50 h.p. at 2,500 r.p.m. shaft speed'. 50 h.p at the crank =, assuming no power loss in the chain, 50h.p at the gearbox input shaft and 50 hp at 2,500 r.p.m = a torque of a tad over 100 ft lb. Assuming a 2 to 1 primary ration the 100 ft lb of grunt at the gearbox = something around 50 ft lb at the crank....... Now IF and I repeat IF i were a design Engineer I would design the gearbox with a safety factor of at least x 2 built in. So IF the 50 h.p. at 2,500 r.p.m. includes the safety factor the box was designed for use with motors producing 25 h.p. with a max torque output at the crank of 25 ft lb....the sort of figures for a 1930s production 500 singles?? Add to that that the Burman gearbox ran the layshaft in bushes allowing more meat between the sleeve gear bearing and bush plus the vast increase in power and grunt being put through the box.........
I remember reading the odd tale in the Norton Owners Club magazine (many years ago (before I and a few older rather knowledgeable Norton owners left the club) of gearbox failures occurring whilst touring Europe and thought to myself at the time ' the dead dont write letters'.
Later I questioned several ex NVT friends enquiring if they were aware of Commando gearbox probles and all stated that they were...some even giving the reasons one being the reduction in primary ratio on Commandos which simply increase the grunt being shoved through the box....
I ONCE had a rear wheel lock up at a rediculous high speed as I swung off the motorway to get up on to the A57 to take me into Liverpool.....LUCKILY I had one of those Kwaka steering damoers fitted and both I and the bike eventually came to a halt still together....bet it was fun riding those factory Commandos around the TT course when the gearboxes were giving problems and rarely managing to complete a lap or two.......Gosh what fun it must of been at high speed between the dry stone walls and rock faces between Ballacraine and Glen Helen wondering when the gearbox was going to fail! No wonder Peter Williams made A FEW MODIFICATIONS!!!!
Wonder what the design criteria was for those 5 and 6 speed gearboxes now being produced to replace the AMC/norton boxes?? I can only remember Mr Quaife testing / developing his 5 speed boxes using Mr Mahoney's AMC race bikes .....
Do hope this does NOT upset anyone.

Interesting info, J.M., as always.

AMC gearbox has always been a bit marginal for 750 and larger Commando race bikes, but has still accounted for a lot of race wins. Going to a higher primary drive ratio, e.g. 1.75, does a lot for durability, but still requires regular inspection of gearbox bits for cracks and tooth erosion to improve reliability. It's not a perfect solution, but in the real world has worked pretty well for racers. I eventually fitted a Quaife HD 5-speed meant for sidecars, and it survived several years of racing with a healthy 920 engine (with a BNR 1.75 belt primary). The new gearboxes from TTI, as well as the latest Quaife designs from Mick Hemmings are clearly a serious improvement, and the clear choice for serious racers (and 1007 street bikes!).

For normal street Commandos, the gearbox seems reasonably durable, as long as the primary is adjusted properly, and it isn't abused by high rpm downshifts. I would cheerfully run the one in this thread with the existing crack in a street bike, but I would tear it down periodically to see if the sleeve bearing stays tight. If I didn't want to bother with that, I'd just buy a new case.

Ken