Date: Thu, 21 Apr 94 14:25:50 BST
From: Peter Azlan <pa@gx2.uk.mdis.com>
A number of people have posted items recently concerning oil leaking from the gearbox, where the kickstart and gearchange enters.
Assuming we are talking AMC boxes here, the sort fitted to Norton and Matchless twins for the last 30 or so years... The boxes outer cover is fitted with two rubber rings which seal the shafts as they enter the box. They are easy to replace and cheep too.
Kickstart seal is 040005 Kickshaft 'O' ring.
and
Gear change seal is 040006 'O' Ring pawl carrier.
I had a leak last year and was supprised to find the little things, easy enough to replace, no more oil drips.
Date: Thu, 21 Apr 94 8:05:02 PDT
From: ralph@swmerc.rain.com (Ralph Merwin)
Peter Azlan writes:
> Kickstart seal is 040005 Kickshaft 'O' ring.
> and
> Gear change seal is 040006 'O' Ring pawl carrier.
> I had a leak last year and was supprised to
find the little things, easy
> enough to replace, no more oil drips.
Thanks! Certainly cheaper than the $35 Fair Spares fix...
While we're talking about gearboxes maybe you have an idea about what's going on with mine. When I get on the gas, especially in first, the kickstart arm starts moving back towards my leg (I've got rearsets). If I don't let off the gas a bit it'll pop out of gear. I can feel the kickstart move in second as well, but nowhere near as pronounced. Any clues of what I should look for first?
Date: Fri, 22 Apr 94 12:47:08 BST
From: Peter Azlan <pa@gx2.uk.mdis.com>
Ralph Merwin writes about a problem with the Kickstarter moving round while 'getting on the gas'.
First a few words from someone who has been inside the AMC box. The gearbox is essentially two sets of gears on two shafts, the Mainshaft and the Layshaft. The mainshaft is where the drive is put into the box, through the clutch centre, (the cluch centre actual bolts to the end of the mainshaft), and the drive comes out of the gearbox on the same shaft through a hollow or 'sleveshaft' riding on the mainshaft, this bolts to the final drive sprocket. When you select the different gears in the box you move the gears around on the shafts so gears of different ratios mesh, providing different speeds at the rear wheel.
There are three parts to the gearbox case, the outer cover which the carries the gearchange and kickstart, the inner cover, which carries the mainshaft and layshaft bearings, and the gearbox case or shell.
This arrangement can probably trace its way back to the first gearbox ever, it is the simplist possible configuration. Modern bikes and cars commonly use three shafts rather than two, which allows for more gear cogs and therefore more gears. I believe Triumph toyed with the idea of introducing a third shaft in their box, but I dont think it ever happened.
From the MOC Service Notes:
>When you think that the AMC box was designed
to cope with 30Bhp from a 500cc machine, it is not suprising >that
on 850cc machines giving about twice the power the reliability of the box
is not what it should be.
RGM manufacture a tougher gearbox shell and sell it for about 200 pounds, Mick Hemmings sells quafe 5 and 6 speed ratios.
Also from the Norton Commando Service notes:
>SLEEVE GEAR AND LAYSHAFT BEARINGS:
>One of the first things to go on an 850, or
even a 750 is the layshaft bearing in the Case. First symptom of
this is
>a kickstart shaft which moves round on
its own and springs back to dig you in the shin. At the same time you
>may get jumping out of gear.
>
>As there is next to no side load fit a roller
bearing equivilent NJ203C3. If all else fails (which it easily can,
once a
>bearing goes) you can remove the layshaft completely
and carry on in top gear only - make the change at the top
>of a long hill though, as the kickstarted will
be inoperative.
The 'layshaft bearing in the case', is the layshaft bearing fitted to a blind hole at the back of the gearbox case, the opposite end of the layshaft to the end that fits in the inner cover. this means you will have to remove and strip the box to change it. When you do, wait till the wifes out and put the gearbox case in the oven to heat it up before drifting a new bearing in.
This happened to a frend of mine, and the layshaft bearing punched a hole in gearbox case as it disintigrated. I towed the bike home where we stripped the box.
I used to think this was caused by running thee box with insufficient oil, I have read somewhere its because the bearing was fitted the wrong way round at the factory. As you can see above, it may just be down to design, or lack of it.
Ralph, fix it now or wait for the bang and face
the possibility of replacing
gearbox case.
Date: Fri, 22 Apr 94 8:35:47 PDT
From: ralph@swmerc.rain.com (Ralph Merwin)
Peter Azlan writes:
> Ralph Merwin writes about a problem with the
Kickstarter moving round while
>'getting on the gas'.
...
>>SLEEVE GEAR AND LAYSHAFT BEARINGS:
>>One of the first things to go on an 850, or
even a 750 is the layshaft bearing in the
>>Case. First symptom of this is a kickstart
shaft which moves round on its own and
>>springs back to dig you in the shin. At the
same time you may get jumping out of
>>gear.
Hmmm... I did replace the layshaft bearing. I'd heard all the horror stories and advice before I got into the gearbox so that was the first task on the list. It's interesting that I'm getting the same symptom though (except for the springing back).
I read through the Service Notes and found your description, plus some additional stuff about the bushing potentially being bad, especially if the gearbox oil is 'gold' (which it is!). Seems that the bushing works against a circlip and manages to grind itself away. Looks like one of this weekend's projects...
From: bman1@aol.com
Date: Sat, 23 Apr 94 05:00:52 EDT
Peter Aslan writes:
>The 'layshaft bearing in the case', is the layshaft
bearing fitted to a blind hole at the
>back of the gearbox case, the opposite end of
the layshaft to the end that fits in the
>inner cover. this means you will have to remove
and strip the box to change it. When
>you do, wait till the wifes out and put the
gearbox case in the oven to heat it up
>before drifting a new bearing in.
This is not true in the vast majority of cases. I have replaced numerous layshaft bearings and have *never* had to pull the gearbox out of the bike - a rather big pain in the ass as you must not only disassemble the Primary drive but also get into that rather inaccesable rear engine mount. All thats necessary is to heat the gearbox casing around the bearing (say witha propane torch) and stick a cold damp rag into the bearing itself then after a few minutes use a puller and out it comes... simple.
Also I think that the danger factor of riding around with a failing layshaft bearing has been understated: Several years ago I had one fail on me while I was only going about 35 mph, the rear wheel locked up completely - regardless of whether or not the clutch was pulled in - and I counted myself lucky not to have laid the bike down or gotten run over by a truck...DONT WAIT TIll IT FAILS!!