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AMC Gearbox oil level

Submitted by graham_pickering on Mon, 16/05/2022
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Commando

I can't imagine it could possibly make that much difference but, as I don't have a center stand it has raised the question of, should the oil level should be checked with the bike on its wheels, or on the center stand?  I use a paddock stand which lifts the rear up really quite high which could make a difference   After an evenings reading I can't find any reference to this point anywhere. (probably because it irrelavant).

During a recent rebuild I changed the outer cover seals for the new square type just as a matter of course, changed the output shaft seal and made a few precautionary changes to help prevent oil seeping into the chaincase, (....which I don't remember it ever did!). I only ever had problems with a leaky output shaft oil seal before, but now the kickstart shaft is leaking and the new output shaft seal is still leaking slightly (makes a good chain oiler), so I am wondering if I am over filling the gearbox. I'm in the middle of replacing the kickstart seal again now, maybe I just mullered it on the spline putting it on but the funny thing is, I finished the gearbox and filled it with oil many many months (years!) before I got to the kicking the engine over stage and it only just started leaking then. Odd!

Submitted by ian_goodhall on Mon, 16/05/2022

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I think the difference between on the stand and off it would be insignificant. It's easy to see the level plug if you look through the inspection cover so you could try on the stand & off it just to satisfy yourself. 

When I fit the seals, kickstart & gear change shaft, I use RTV silicone seal in the groove that they fit in, then fit the seals and let the silicone set before fitting the cover. No idea if it makes a difference but mine don't leak. 

Submitted by paul_griffiths on Mon, 16/05/2022

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As the bike will spend its time on its wheels when it is being ridden this is the attitude the oil level volume needs to be set to.

My Combat came with a breather hole in the filler cover! I can only think this is to allow for the pressure of heat expansion to dissipate as the gearbox warms up and therefore stop oil being forced passed the shaft seals.

Are you fitting the output shaft seal the right way round with the spring facing into the g/box?

Check if the countershaft sprocket spacer is in good condition especially the area of contact of the output seal if in doubt replace it.

Graphogen all seal contact areas on reassembly.

Submitted by mikael_ridderstad on Tue, 17/05/2022

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According to the Mike Hemmings DVD, the hole must be clear to prevent rusting of the parts fitted in the outer cover. Mk III had the hole moved to the outer cover.

Submitted by graham_pickering on Tue, 17/05/2022

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I'm sure the difference in levels on the stand or off will be negligible. I'll do as Ian suggests and have a peer down to the level plug when I take it off the stand. It makes sense that it should be levelled in the riding position though. 

I did put some goop in the seal groove this time (I used Weller seal as I didn't have any suitable silicone based products to hand).  It could be that the seal stuck to the kickstart shaft in all the time it was sitting before I used it and then maybe the seal was turning in the groove which made the leak worse and worse. I'll fill it with oil today and see. 

The leak from the output seal is more dissapointing as its so much more work to fix. I did fit it properly and replaced many parts that could affect it so why it leaks is a mystery. I've only done 11 miles since the rebuild so I'm hoping it might 'bed in'  :-)  Unfortunately things rarely do though. It only leaks when its being ridden so far though. Before the rebuild it would drip on the floor even when static. 

Regarding the breather hole, after some considerable reading I ended up enlarging mine as I got the impression it could help prevent oil seeping into the primary case along the clutch actuator tube and all sorts of other minor expansion and contraction type benefits. I didnt see that it could do much harm and if it does a replacement inspection cover wont break the bank! 

Submitted by alan_hesslewood on Tue, 17/05/2022

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When fitting seals over splines, it`s worth putting a couple of tight turns of electricians tape over the splines to the end of the shaft then a lick of lube to help it on.

Best regards, Al.

Submitted by richard_mills on Tue, 17/05/2022

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Don't give up yet on your output seal. About a year ago I replaced the seal behind the input flange on an MGB axle; distorted it on fitting and tried with a second seal. Job done OK but it leaked worse than ever. Decided that I couldn't do a better job so I would put up with it. A few hundred miles later and it stopped leaking (oil level in diff. correct) and hasn't leaked since. Long shot, but same might happen for you. Here's hoping!

Submitted by andrew_mackenzie on Fri, 20/05/2022

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Graham, are you sure the output seal is actually where the oil is coming from? It can also run along the shaft past the inner diameter of the spacer and appear to be from the seal. Not easy to see when everything is  assembled. If the seal had been fitted to the housing squarely and then the spacer inserted, the insertion of the spacer should not have been able to damage seal, as it is going into the gaiter from the open side and simply spreads the gaiter, if that makes sense?

Andy

I think I've got what you mean Andy.  I'll have a look at an exploded diagram to be sure though. I went for a 25 mile ride on Friday just to get a few miles on it and when I got back the tell tale signs of oil flicked off the chain and streaked by centrifugal force on the left tyre wall were not there.  Maybe the first ride sprayed oil I'd used on assembly or the new chain was too heavily oiled? or as I joked, it has bedded in. The kickstart seal no longer leaks either! ( oh...did I fill the gearbox with oil?)  More riding is needed I think!  Lets hope for a bit of nice weather (UK) 

 



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