My M20 barn find is now up and running and on the road. Starts well, leaks only minimally and has been reliable so far so I have little to worry about. When I refurbished this machine I was not keen to strip the box for no reason as all seemed well on the bench. I cleaned it out and I replaced the kickstart spring and rubber block. Now it's on the road I find first gear difficult to engage from a standstill, but all other gears seem to go in well, although false neutrals seem to be a feature! I won't do anything about this until winter, but any ideas as to what I should focus on would be appreciated. I imagine my winter project will be to strip the box and inspect, measure and replace as required. Love the bike though and the interest it receives wherever I go!
Clutch was first thought but it checks out fine. Rolls forward and back easily with clutch engaged but in gear. Also clutch had had a lot of attention and I'm sure it's working as well as it can. I will take the side cover off and investigate adjustment - I'm not really that familiar with this box and I'm still learning!
Mike your gearbox sounds like a typical M20 box. I had the same problems and despite several strip downs they remain. They have improved as I have putmiles on the bike due to a combination of acceptance and gearchange technique developement on my part.
If you read the army riding instructions for the M20, you will notice some differences, compared to the BSA manual, on how to engage and change gear, so clearly they were bothersome from new. In summary to engage first from neutral when stationary: pull in the clutch, apply pressure to the gear lever and gently rock the bike back and forth until 1st gear engages. Keep applying the pressure to the lever as you let out the clutch and the bike moves off.
I have spare neutrals but they are less pronounced if I make the effor to change gear slowly. To ensure I always get 4th I keep the preesure on the pedal as I let out the clutch (I can feel it engage as I am letting out the clutch).
Some days I curse the gear change and on others I call it 'character'.
Thanks Dean, that's all very interesting. Clearly first seems to be the troublesome gear. For me clutch in, short pause then shift up or down slowly, but firmly, gives generally good results. Actually when when slowing and needing to change to first it's also OK. It's the shift into gear from a standstill that gives me most trouble. I will try the rocking that you described and I'll look at adjustment in a couple of weeks when I have some free time. I'll post the results of any adjustments that I make.
Mike, if you want to try adjustments you will find very useful advice in the technical sections here
http://www.wdbsa.nl/Gear%20Change%20Control%20Rod%20Adjustment.htm
and here
http://www.wdbsa.nl/download/Gearbox%20work.pdf
I am interested though in what is being adjusted. Can anybody explain?
Mike,
Adjusting the control rod doesn't really take up slack but fine tunes the position of the selector forks. Lengthening the control rod will move the selector forks towards first and third gears thus improving their engagement, shortening the rod moves the forks towards second and forth. Improving selection in one gear may adversely affect selection in the others.
False neutrals are symptoms worn parts or mal adjusted selectors.
Remove outer cover. Inside top right is an adjuster rod, wind it out half a turn. Worked for me.
Ian,
2 things about your solution to the problem.
1. The rod is sligtly bent, therefor can't be turned half, only fully - one time.Is that OK ?
2. If you do so, is there the risc you can't reach 4th gear anymore..?
Sorry I didn't make it clear. remove pin from clevis on the straight end of rod turn clevis out half turn. This will push the selector better into first gear. This was all I needed to engage first without altering the other gear selections.
Ian I'm hoping that what worked for you may work for me so I'll have a go next week. If not, as I don't have a winter project the gearbox will be it! I can live with it until then.
Ian I'm hoping that what worked for you may work for me so I'll have a go next week. If not, as I don't have a winter project the gearbox will be it! I can live with it until then.
Let us know if this works, Mike.
Very interesting !
Getting slightly off topic I looked at the interesting article Ron posted re Hans Muller. He states never use modern EP transoils as they are not compatible with bronze or brass and eats them away. I did have that experience rebuilding a Ford Model A gearbox where the thrust washers were non existent and floating as particles in the oil. As I am not sure whether I used a 80-90 EP oil in the gearbox of the M20 I have drained it. The workshop manual specifies GO 90 oil but Hans Muller specifies SAE 40-50. The only supplier in Australia that caters for old vehicles is Penrite oils and they have a gearbox oil SAE 40-50 and a Transoil SAE 90. Both non EP oils compatible for ferrous and non ferrous metals. As the M20 doesn't run a seal on drive end thinner oils leak out much easier.
What are people running in their gearboxes. Australian summers get quite hot compared to Europe so I was thinking maybe the SAE 90 as per the manual. Penrite state the SAE 40-50 is used where the manufacturer specify engine oil as was the case in the 50's and 60's. Interested to here any comments or opinions.
Thanks Ron. I rebuilt my M20 some years ago and never thought about fitting a sealed bearing at the time, as you state. I don't intend to strip the gearbox at this time as all is okay so oil leaks are part of the journey. I will try the SAE 40-50 then and see how it goes for leaks. I have fitted sealed bearings as you describe to a later rebuild on a M21 as well as on the drive side outer main bearing to stop oil seeping into primary when it wet sumps and yes it makes them quite oil tight.
I had the same issue. Cant get in first gear. Did the half turn on the arm thing and the result was i have first gear but couldnt get it in third or fourth anymore 😣. So changed it back and have no first anymore.
My M20 first gear doesn't want to engage easily. I find if I role the bike back or forth a few inches it clicks in OK. However, It's not conducive to a quick get away when you're first in line at the traffic lights. Ron
Making adjustments to the selector dog positions using the tie rod isn't a 'cure all' for poor gear selection, only a possible solution if the gearbox was incorrectly set originally or there is slight wear...
More severe component wear, incorrect shimming of the shafts within the box, the overall condition of the clutch and its adjustment can also all have an effect and require remedial work to obtain a good result...
Due to the convoluted design of the selector mechanism from the ratchet and pawl assembly through to the selector forks and dogs these boxes, when worn, can suffer from 'lost movement' and this affects their ability to correctly engage the driving dogs and thus gear engagement...This is compounded or exaggerated by incorrect assembly where the shimming of the three shafts within the gear case is not correctly carried out...
Further, boxes that have been incorrectly set up in the past can have a disproportionate (rather than general) amount of wear of the cam tracks in the selector forks, the pins the forks run against, the selector fork ends, the operating grooves in the selector dogs and the main shaft splines at the sleeve gear (4th. gear) end of the shaft...
These conditions all affect overall movement but the last is particularly important...If the spline ends are badly worn the shaft will not be in the correct position within the box even when correctly shimmed...
Finally, some gearbox components were modified to improve gear engagement..There are two forms of selector dog teeth, both on the sliding dogs and the gear faces and certainly at the time of the full rebuild of a WD box fitting of the later types is worth considering...
Also the cam tracks and pins were modified by increasing the pin diameter and the track width...This produced wider radii in the 'corners' of the cam tracks at the point where the selector forks change direction...This smoothed out and eased the change of direction...These later fork assemblies can also be fitted to WD boxes without modification...Ian
Ian, I have a pile of surplus WM20 and later "kidney bean" gearboxes. Most are disassembled and piled in a box. My WM20 now shifts more or less reliably after many adjustments and repairs, including steel inserts in the mounting lugs to correct ovality and movement in the plates. I agree that shimming all 3 shafts is the essential first step.
I keep reminding myself that the WM box was the first design after abandoning the hand shift and marvel at the progressive simplicity of design and function over a scant dozen years!
I will be building gearboxes for a hot rod '46 B33 and my '50 ZBGS this winter. How can I identify the desired "later type" engagement dogs? Should the sleeve gear be an interference fit on main shaft?
Well ,I was quite chuffed at the level I'd managed to get to on my rebuild with being a total novice on the WM20 , BUT after reading the comments and advice in relation to the rebuilding of the box , I think I'll leave it alone now till I find someone who can do the job properly for me :face_with_rolling_eyes:
Hi Jeff...The sleeve gear is top gear (the bushed one that the sprocket fits to...)...The 'double' gears that fit onto the shaft splines should be a fairly good press fit...A hydraulic press is usually needed to remove or fit them...
If you look at the dogs in a WD box the top faces of the 'teeth' are completely flat...The later ones have quite distinct angles machined onto them...Whichever you use, go for dogs that aren't worn on the corners...They just have a slight radius on the edges when new/good...
Dave.. ['I think I'll leave it alone now till I find someone who can do the job properly for me']
Don't do that..By buggering around, thinking about it and reading everything you'll work it out OK...Give it to someone else and you'll learn nothing...None of us knew anything to start off with...Ian
Your right in what you say :)I'll not learn nothing if I don't attempt it .
I've been trying to find the oil flinger washer 24-4235 ,the one that sits behind the spacer 24-4237 on the end of the mainshaft before the inner cover goes on ,mine didn't have one fitted .
After searching the net I managed to find one in Germany which I now have .
I have read that some M20's probably left the factory without these washers fitted! Where it fits wouldn't this be classed as a combined spacer/oil flinger washer and if not fitted wouldn't this cause premature wear in the gearbox .I have also read while scouring the internet this washer isn't critical?,surely if this is fitted as per factory its fitted for a reason, now things are getting a little confusing reading different views on it .