Gearbox rebuild question

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MexicoMike

MexicoMike

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I posted that I plan to disassemble the gearbox to check everything out but I'm having second thoughts of the "if it ain't broke, don't fix it" type. THe box could not possibly work any more smoothly or positively in every way than it does right now. So...am I correct in understanding that if it has the "bad" layshaft bearing it could be working perfectly today and blow up tomorrow? From all my reading it appears that there is no way to make this determination without complete disassembly, right? I feel that if I disassemble the gearbox I should go ahead and replace all bearings/bushings since I'm in there even if they all seem OK. How do folks experienced with these boxes feel about that?

My 850 is a bitsa and I have no idea of the pedigree of the tranny as far as original year or what bearings were likely in it or if that's even possible to determine by the serial number.
 
When the layshaft bearing went out on my first Commando (a 1973 850) there was no warning. The gearbox locked up when I was riding down the highway. Deserted road, so I survived. How would you like to have that happen while riding in traffic? Are you willing to risk your life over a $60 bearing and a day or two of work? Both of my current Nortons had the original bearings. Assuming that some previous owner must have upgraded the bearing could prove to be a fatal mistake.

Debby
 
"if it ain't broke, don't fix it" type sums me up, with the exception of good brakes and unintented application of brakes :shock:

If you go in just to do the bearing and leave the primary alone its not too bad, I heated the nearly empty case up with a blow torch and from the primary side hit a solid piece of hardwood resting on the layshaft bearing housing, 3 blows later it was sitting loose inside the case.
 
I took my gearbox apart to make sure it had an upgraded layshaft bearing and did not replace any part except the ratchet pawl spring (the one with the bent lower leg) and the cover gasket. The gearbox works great.

Greg
 
OK, I disassembled the box in place - I pulled all the gears/shafts. NOW...I can see the layshaft bearing and it's a roller bearing but I can't see any markings. It appears to have a fibre cage as opposed to a metal cage. Does this tell me anything yet as far as being the right/wrong bearing? Every other part in the box looks new - no wear on gears or anything else.
 
Uh, found the answer to my question right on the OB site - the layshaft came out as per this item in the OB guide: "2) the shaft and inner race come out of the shell. This is fine, because it means that the bearing is a roller bearings. "

So the bearing is the proper one and I can just put the whole deal back together. One interesting item - the drive sprocket nut was not even finger tight. After removing the keeper I was trying to figure the size of the nut and when I just barely touched it, it unscrewed!
 
My roller bearings had plastic cages, so the bearing sounds good. I'll defer to the experts on how to ID it for sure though.

A few other things to check while you're in: kickstart pawl, cracks in the kickstart shaft (at the bottom of that V notch), and end play on the kickstart shaft. You can shim it as required with rear iso shims (see the OldBritts tech article). Sounds like a previous owner has done a full rebuild, so you're probably good to go. The shaft crack is easy to miss though, so check carefully. My 850's was cracked and I almost missed it.

Debby
 
Debby - thanks, I'll make those checks.

Here's a pic of the bearing in place:
Gearbox rebuild question
 
Looks good to me Mike, Also looks nice and clean in there. I think you did the right thing by checking, Now there is no question the box is sound.
 
After further cleaning/checking I found that although the layshaft bearing seems in perfect shape - very smooth turning with everything clean and the layshaft shaft inserted back into bearing - the main shaft ball bearings are brinneled (sp?) so I will replace those. All other parts - gears, bushings, kickstart pawl, shafts, etc look great, even under a magnifying glass. The kickstart shaft has some of its splines sort of goobered up but the kick start lever was very tight with no play at all - doesn't seem like a problem. But I have to admit that the pic on the OB site showing the kickstart shaft with some messed up splines looks about the same and Fred, in his article, said he'd replace it...
 
Mike, I noticed on a kick start lever I had purchased a while back that they didn't machine the splines a the way around. Where the bolt goes through they stopped short, I think this was done to keep those from being broken off during tightening. I don't think the old ones were? Or maybe that was the first time I noticed it? I don't think it will hurt if that is where they are broken.
 
Grinding the splines off in that area on the lever is an old trick for getting a loose kickstart lever to tighten down. AN is doing it for us on the newer levers. I noticed that on the new one that I bought for my 850 also. No worries there.

Those splines are fine and easily damaged, but if the lever goes on and tightens down then there's no reason not to keep using those parts.

Debby
 
There was also a recent thread I read that suggested opening up the hole the bolt goes through before it gets to the threaded part because when you tighten up the bolt, it twists the angle of the un-threaded part and makes it hard to tighten and binds the bolt. I haven't done that but am planning on looking into it because I can tighten mine, but it is very stiff to do and the more I tighten, the harder it gets, kind of like it's binding. I also think a flat washer on the bolt would help, it wasn't on there originally.

Dave
69S
 
My philosophy is to do the easy things first because I'm a might frugal.
Opening the pinch bolt hole clearance portion worked on my kicker because that was the only problem.
I think it better to analyze each situation individually to determine which fixes are needed and then carry them out one at a time in order of greatest improvement potential.
If the newer kickers have some splines omitted by the bolt hole I think that is an improvement. Getting them all to tighten simultaneously is just about impossible anyway.
Lubricating the splines to help them seat against one another during tightening would help too.

If you think seriously about what happens around the circumferential interference, spline to spline, then pretty soon you need a drink.
That's where I'm at.
 
All the posts re the splines are great! The splines are messed up exactly at the position described by others and I have often thought about the pinch bolt and how it binds when being inserted/tightened and how to improve that fit. EXCELLENT stuff and I will not be replacing an otherwise perfectly good kickstart shaft. Thanks...
 
And another question - that I should have posted earlier...

Re clearance in the bushed gears: The shop manual and the OB article talks about checking for "excess" play caused by bushing wear. But nowhere is there any figure for the "excess." Is there some figure for wobble/play using a dial indicator at the edge of the gear that would be useable? It doesn't seem like a lot but there is some wobble with everything clean/dry but I can't tell if it's too much or within "specs" (whatever/wherever those specs might be). I'd buy a bushing set but I'd kind of hate spending the money to then discover that the wobble is about the same...

???
 
For interest, I have just had my gear box pulled down, I replaced the bearings with sealed types:

1654-2RS
6203-2RS
RLS2-2RS
 
Mike, be aware that if you put new bushes on anything, you will have to have them reamed to fit. They do not automatically make the tolerance correct.

Re: sealed bearings, I'm not sure you want a sealed bearing at least on the inside of the mainshaft bearing next to the sprocket. It will get lubed from inside the gearbox, no? The layshaft doesn't need to be sealed either. I stand to be corrected as usual.

Dave
69S
 
Really (reaming)? OK, I don't have the facilities to do that - at least to do it correctly - so I'll accept the current slight play as within spec! :)
 
DogT,

The sealed bearing requires no external lubrication ( they are packed with MDS ), when you chip a gear, it will not take out your bearings.

If a bit of oil leaks into the bearing, who cares, as long as the debri is kept out.
 
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