false neutrals in 74 CR450

[Gippslander]

Hi,

Getting a lot of false neutrals in my 74 CR450, did a search and found where Fernando from Husky Parts was selling a Mag 250 engine and in the description he says "new gearshift mechanism roller to eliminate false neutrals"

And from memory the mag and the CR400 and 450 used the same gear layout so the selector drum should have the same slot pattern

Can anyone tell me about this "update"?

Thanks

[Brian Watson]

I don't know anything about a "new" mech.. but you will get a false neutral, particularly when downshifting.. if you do not make  a "positive" push on the gear lever, you can end up in angel gear... especially if you are on the over run into a corner..I found if you really stomp on the gear lever..no problems..

[Rossvickicampbell]

rough as guts Watto - rough as guts!!!  fast - but rough as guts!

[Brian Watson]

Come on Ross.. Godbold's faster than me..   maybe not as rough as me granted..but faster than me..

[Rossvickicampbell]

yeah right - he is a burglar!

[Gippslander]

Thanks for the advice -- and the humour 

Spoke to Fernando, he was helpful but the fix he had mentioned was the oil relief and chamfer fix for the detent plunger, mine has that mod already.

Have had a look at the 76 on gear detent system, seems a lot better, have the parts for that and am going to see if I can graft it onto the 74.

The drum rotation for the later 6 speed boxes with the better cam/roller detent system is 21deg -- same as for the 74 -- and the shaft spacing and fork pins and shift drum distances are all the same as well, will do a mock up and see.

Only problem will be drilling the shift drum to tap for the 6mm screw to hold the cam down, drum is  hard, may be only case hardening so may be able to grind through the surface to some softer metal, or could do a tig spot but will get weld shrinkage so that will lift on the other side so will need to be clamped down and also may have to heated the tig spot red (and clamp down on other side) to relieve the shrinkage etc etc.

Have got it apart and am not going to put it back without doing something 

[Gippslander]

Have done the modification, fit a late model 6 speed shift detent system into an early 5 speed gearbox

Bike is 72 CR450 husky
Was hard to find neutral and kept finding false neutrals, was a pain on the track
Pictures tell the story


Trial run, neutral on the old detent in the hole on the bottom of the shifter drum and neutral on the new detent plate and roller arm on the top of the shift drum


Trial run to see if second lines up, yep -- "proves" that the degree rotation of a five speed shift drum is the same as the degree rotation of the 6 speed drum


Machining the boss on the top of the shift drum so that the late detent plate goes on, note - do not take any material of the drum itself - it is already the correct height, just make sure the surface is flat, mine had a small turn up near the edge so I got that flat.
The drum was case hardened, once you get through that it is nice steel to cut


Test fit of the detent plate, neat fit - no play


Lock pliers to hold the plate in the correct position so it will be timed correct when taking it out to weld.
And be careful to have the shift pin standing up straight because it can lean over a little and you may not notice it and you will have incorrect shift detents for the gear engagement


Used an Arc welder, was not a neat weld, am usually ok but was crappy -- may be the case hardening?


The shift fork guide tube needs to be shortened to allow for the roller arm and spring assembly


cut off 6.63 mm


The new assembly has a height of 53.5 mm


The available space in the cases is not quite 53.5 mm so plus a bit for the gasket and then some allowance for working clearance all "adds" up to needing to remove .3 mm from the cases


Econo mill :-) my drill press with an end mill, take .3 mm of the boss for the shift pin to give the working clearance and also remove the crosshatch on the case so there is no catch point for the detent spring 


Ready to assemble