Hi, I just purchased a WD M20 on Tuesday, it seems to leak a fair bit of oil from the gearbox. Is replacing the gearbox oil with semi fluid grease an option or am I going to damage the gearbox if I do this.

thanks, Neil

Some of our gearboxes run on grease or semi fluid grease in the gearbox. But an M20 is designed to run with oil, otherwise some of the bushes and sliding parts don't get lubricated properly.
The only proper cure is to strip the box and replace the large bearing in the drive end with a sealed bearing. These bearings are sealed with a pressed in neoprene strip each side and it's best to lever out the seal on the inside of the box. Ron

email (option): ronpier@talk21.com

I am in the process of restoring a 1943 M20 with the older style gearbox that has no oil seal on the output shaft. Assuming that this is your largest leak location, it is because the oil 'slinger' (the scroll thread machined into the output sprocket shaft) does not sling oil back into the gearbox when the shaft is not turning. Mine leaked all over until the gearbox was almost dry. I guess that in 1943 i ws cheap and Ok to leak everywhere. I want my ride to be as leak - free as possible.

My solution was twofold; 1. Use a thixotropic grease, one that has a dramatic viscosity decrease upon shearing, and a thick paste when not sheared. This will ensure the slinger works when the output shaft is turning and the grease does not flow under gravity when the shaft stops. After some research, I use Schaeffer 274 Moly E.P. Synthetic Plus Grease NLGI #00. If you Google Shaeffer Oil, You will only find dealers that want to sell you 55 gallons or more. I contacted Shaffer directly and found out from the lead engineer that the grease does in fact penetrate all areas that are subject to shear, like bearings, bushings, gear faces, etc, providing full coverage of lubricant. They thoughtfully provided an internet vendor that sells small quantities:

http://stores.buyschaefferoil.com/schaeffer-grease-274/

2. I installed a leather washer between the gearbox case and output sprocket to contain any grease that might try to leak out. The gap between the sprocket face and gearbox case on my ride is about 60 mils, so I used a leather washer cut from an old shoe that was about 80 mils thick, soaked in motor oil for a few days. It did leak a few drops of oil when I used the bike again, but stopped after a day's use, and no leaking grease.

The grease is easily pumped into the gearbox with a standard grease gun. I used about 2/3 of a pint, as the gearbox is listed as a 1 pint capacity, and filling a gearbox to capacity with grease invites trouble.

Dave Wadiak

email (option): dwdiak4@gmail.com

Interesting....

Would it be correct to assume this (E.P.)grease does not contain the sulphur and phosphorous based additives that adversely affect bronze bushes?...I know there are some moly greases that have that specification...

Also am I reading it correctly that the grease becomes fully liquid when the gearbox is running, returning to a solid/semi solid state when cooled...?

This needs to be the case, as without a fully liquid phase I can't see how it would pass through the shaft and bush drillings to reach the various points requiring lubrication (or the gear selector parts in the outer cover...)

The lack of modern seals in the gearbox wasn't a question of cost...These boxes pre date the introduction of lipped neoprene seals and sealed bearings..

So, along with most other boxes of the period they employed a selection of cork/felt/leather seals to try and keep the lubricant in with varying degrees of success...BSA moved to oil filled gearboxes in the pre war period despite this fact...Some manufacturers stuck with semi fluid greases which were commonly used from the early days of motorcycling...Ian

email (option): ian@wright52.plus.com

The technical lead at Schaeffer oil said it was safe to use with bronze and brass bushings and other small non iron and non metallic parts. They claim to have many applications on the books.

I was assured that the fluid grease gets everywhere under shear conditions, that's the point of using a thixotropic grease. To make the point my kickstart bushing weaps a very small amount of the black (yes it is black in color) grease on occasion after use. It's a long way from the main gearbox cavity to the kickstart shaft bushing.

From my perspective, I plan to see how it lasts in service. I have had no shifting problems or serious leaks​ to date. In any case at my age I plan to use the bike to the fullest. If the grease attacks the internal parts I will let the next owner do the repairs.

Merry Christmas and happy motoring!

email (option): dwdiak4@gmail.com

It will not get into the layshaft bushes nor will it properly lube the change forks as there is nothing to force the grease into the oil hole or under the fork.
The gap is just not big enough.
Oil runs down the casting and fills up a lube well on the top of the layshaft then gravity "pushes" it into the bush aided by capillary action.

This does not happen with grease and it is only a matter of time before the layshaft bushes will be oval and the change forks start to stick so do not sit centered in the slot in the sliding dogs which will cause excessive wear in the fork.
The output shat bush has nothing to cause the oil to flow through it other than capillary action and this will not be enough to get sufficiant grease through there to properly lube the bush

The problem is oil slingers and wicking spirals require a specific clearence to work properly
Viscious friction , aided by the odd bit of grit wear the output shaft hole oval so the slingers just don't work because the gap is too big.
Ditto with the kick start & gearchange shaft.

If you stop and have a think about it,
You are filling the box with grease to prevent it dribbling out gaps in the .010" to .040" so how the hell is it going to get into a space that is .003" to .005". The two do not add up.

email (option): bsansw1@tpg.com.au

Trevor

Do you have some data to suppoort you claim? Otherwise you are just another opinion.

Dave Wadiak

email (option): dwdiak4@gmail

Dave I pointed out at the start of this thread what I think is the problem with grease in an M20 box. It's been explained and elaborated on by Ian and I think what Trevor says is basic physics.

I've just put semi fluid grease in one of my Royal Enfields (The book says axle grease, thinned with paraffin) which is supposed to be installed when the gearbox is built.(there's even no drain plug provided). I found that by heating the semi fluid stuff in a pan on my camping cooker it quite soon became fluid enough to put in a pump oil can for the filler neck. I've no idea how hot or fluid it becomes under normal operation though?

The Burman boxes in my Matchless's also require Semi fluid grease. Ron

email (option): ronpier@talk21.com

I would think that this would be a perfect "trial and error" experiment.... Dave mentioned that he would use the bike at its fullist....so, if no or minimum wear can be found after 25.000 k or so, it probably works....if not, it will be another costly repair and the forum members are again a bit wiser....

email (option): mr.bighealey@hotmail.com

Anyone who goes out to the garage in the morning and isn't greeted by the smell of thick old oil seeping through felt is missing out on one of the great sensory pleasures of owning an English motorcycle.

The greatest argument against experimenting with gearbox lubrication is that sudden and catastrophic gearbox failure is just that...catastrophic. It doesn't matter how quick the rider's reactions, pulling in the clutch doesn't help with a gearbox seizure and it's not the 'Technical Lead' who has his life on the line. It's most unlikely that their product has been tested in a BSA transmission.

Underfilling an M20 box on the grounds that "filling a gearbox to capacity with grease invites trouble" is probably not a good idea. As I understand it, the M20 box is effectively a V-twin transmission turned on it's side in order to make it fit and unlike the majority of similar countershaft boxes, it does not have the benefit of a layshaft at the lowest point which will deliver oil to the other parts even when the level is low.

Bikes such as Ian's and Ron's are witness to the fact that with a sealed sleeve gear bearing, careful assembly and a preference for the rear rather than field stand, these boxes don't have to deposit a puddle underneath at every stop.

To be honest I am dubious about the ability of grease to correctly lubricate a gearbox designed to carry oil...

Trevors comments on why grease is being used ref. leaks and relative size of 'internal' and 'external' clearances of the box are a valid observation and entirely logical...

Nevertheless, I'm not against experimentation, I have done it myself numerous times with modifications and clearance alterations...

If nothing is ever tried nothing is discovered...I'm with Maarten on this one..Let's see how the experiment goes over time...That's the ultimate test...Ian

email (option): ian@wright52.plus.com

Yes, I agree with Maarten and Ian on this. It is a generous offer by Dave to test the 'grease issue' on behalf of all us forum members who have, over the years, pondered on the subject. It is all going to be down to whether the spec of this grease is different enough to the basic types we put in our grease guns to do the job. I think the verdict on 'standard thin stuff' is already known, so lets not be too hard on a guy who is willing to field test an alternative for us. Duncan

I have a stuffed gear box.
I have clearences for the oil slingers on RR V 8's .
Right up to the end of the 6.75L V8 it had a slinger front & back on the crank.
Allowable clearence was around 0.002" and std was .0005" to .001".

Is that what you are looking for ?
I put 000 gear grease into my box on the advice from some well respected vintage bike owners.
The box ran for about 5,000 miles before I started to get some changing problems which I should had addressed.
It had brand new layshaft bushes put in along with a new countershaft bush.
The layshaft was blued on the end when I took it out, so it was running very hot.
The feed hole for the far end of the layshft was blocked with dried up grease so it had been sitting there & not wicking in like oil is supposed to do.

I am a mower mechanic ( currently ) and pull down a lot of mower, tiller & auger boxes that run in grease. The passage ways for grease to pass through are substantially bigger.

Liquid grease is designed to be pumped into bearings under pressure, not flow under gravity ( that comes from the grease manufacturers ) which is why you buy it in 20lb tubs.

Now if some one wants to try it, they are welcome.
I have done my bit the are free to ponder what I have said or ignore it.

A flatmate rebuilt his box into a set of NOS cases.
His did not leak mine did.
His was full of oil & mine was full of grease

email (option): bsansw1@tpg.com.au

No kidding about the leaks. Mine pours out oil just sitting there. I find the bike doesn't shift as comfortably as it should unless the oil is full up and if it's full, it leaks bad. I can't imagine how they operated like this given how oil was an important war commodity, what else did it get wasted with?

email (option): paulscutler@gmail.com

They didn't leak much when new, that was the whole point to the previous postings.
Get a NOS outer gearbox cover and have a look at how much smaller the holes are.
Ditto on the shell.
Just like air through a radiator with and without a shroud, there is a limit to how big the gap between the scroll & the case can get before the viscous friction within the oil being pumped back in can not bridge the gap between the scroll & the case.
If your box won't change unless it is full pull it out and have a good look at the layshaft shift forks and the timing side layshaft bush.
Better than average chance the bush is oval so the forks have been rubbing on the ends and gone through the case hardening

email (option): bsansw1@tpg.com.au