1978 500w Transmission shift trouble

[Canuck750]

I have reassembled a 1978 Moto Morini 500 motor after having a crankshaft regrind and bearings replaced, no changes to transmission or shift mechanism. Very hard to get shifter to work, stripped motor today, no visible issues. If I remove the shift mechanism I can rotate the top of the shift drum by hand and get the shift drum to rotate 270 degrees. Once I fit the shift mechanism with the two spring loaded arms it is very hard to get the drum to rotate. I have a special tool that holds the four transmission related shafts in place with the gear cluster and shift drum set into the left hand engine case. The detent and shift pawl arms and surfaces appear to be ok with some wear on the shift pawl. It takes a real force on a shift pedal and several stabs at it to get the shift drum to rotate. This is my first Morini and its all new to me.

Drum rotates about 270 degrees





condition of shift pawl and detent



I was complete up to here with the restoration until I tried shifting the transmission



Back to a dissasembled motor and scratching my head


Advice much appreciated!

[Canuck750]

I fiddled with the gear set and shift drum and by adding a second shim under the shift mechanism stud the shift and detent pawls now rest slightly higher on top of the shift drum, this seems to have helped a little.

Now that the shift pedal moves the selector drum it looks like the pawl is maybe too worn to fully rotate the shift drum.

I took a picture of each position I could get the drum into using the shift lever

1st



pawl teeth not engaging any pegs but the detent is locked into a lot

2nd



3rd



Pawl not centered on pegs

4th



This sorta looks OK but the pawl is not centered on the pegs

5th



detent not engaged in 5th, looks like the drum should rotate further but it won\t rotate nay further

I think I need a new selector pawl ???

[72degrees]

Did you remove the 'stopper plate' as part of the strip down?

[Canuck750]

Did you remove the 'stopper plate' as part of the strip down?

I did not but last night I did remove the two nylock nuts and found there is no adjusrtment to the plate.

The manual says to carefully bend the selector spring to center the shift pawl between selector drum pawls, how one is supposed to bend the rigid selector spring tangs is a mystery to me but it is obvious that the selector pawl is not centering between the selector drum knobs as per the manual.

Hass anyone altewred the stopper plate with oblomg holes to allow for adjustment of the stoper plate position?

[Canuck750]

Pretty sure the selector arm is just too worn out.

I elongated the holes in the stopper plate to move it closer or further from the selector drum this had the effect of either getting 1st or 5th to lock into the detent at the expense of loosing either the corresponding opposite 1st or 5th detent lock

Hopefully the selector arms are still available, email sent to NLM.

[Canuck750]

Stuart diagnosed the likely problem as a misplaced shim, sure enough I was missing a shim between a shaft and the engine case. That tiny thickness raised the gear cluster so that it now shifts as it should back and forth through five gears + neutral

THANKS STUART