Hi just a query please. Often when riding my M20 bike I get false neutrals when charging gears. Some people have suggested it indicates worn gearbox, but I have heard others says that it was common to get false neutrals in new bikes with new gearboxes that had just left the factory floor ? So I am just trying to understanding if I need to worry or if it is just part of the normal experience of riding these old bikes ? And if it’s true that false neutrals may have been common on new M20s when leaving the factory. Also I understand its about technique when changing gears - any thoughts appreciated thanks
There is a neutral between very gear.
It has to come out of one gear before going into another.
If the gears and dog rings have been spaced correctly and everything has plenty of clearance, it should almost fall into the next gear with the help of the sector shaft and indent spring.
The gearbox does not like fast changes, you feel with the gear lever it coming out of one gear and then going taken into the next.
Pressure must be kept on the lever until you feel it go all the way.
It takes time to learn.
Mark has identified one of the differences between the M20 box and later types...The large gears have a lot of inertia, so it takes more time for them to change speed for gear changes...The key is to let the gearbox take its time..'Racing' gearchanges, or even those at the speed you might use on a later swinging arm gearbox will find these false neutrals and are definitely out!!....Like everthing else on an M20 it all happens at a leisurely pace..Take your time and you'll find you will soon achieve 'clean' changes...Ian
One more thing (2 really).
1. Are postwar M20 boxes better in this respect ? (they have slightly different gears/dogs)
2. Can you put all the internals of a postwar box into an WM 20 housing without trouble ?
In post war boxes all the selector assy., gears, selectors, dogs and shafts etc. are dimensionally the same as earlier examples overall..The larger heads of the selector fork pins and crucially the resulting larger radii in the selector fork tracks smooth out the action there by reducing the sharpness of the 'corners' that the pins have to go round ...Later sliding dogs and the matching teeth on the gear faces had the shape on the top of the tooth altered to ease engagement...The layshaft of the later boxes has the speedo drive worm machined into it but it will still fit in the earlier box...Ian
The Norton box of the period, the "Doll's Head" is also notoriously long-travel and gear-changes can be missed. With very little in the way of internal alterations, it became the post-war AMC box with a nice short crisp change. The difference lay in the positive stop mechanism.
Riders in the 1930s were moving on from a gated hand change and were used to a one-two-three, one-two-three way of changing. Close the throttle, let the revs drop, feel the gears in...My feeling is to get them into top as soon as possible. The 1:1 design means that there is much less load and wear in top. The top gear roll on is where the pleasure is.
