1961 Dommi 88 gearbox

anji mehra

Joined
Feb 28, 2017
Messages
7
Hi
Just joined the forum & not sure if Iam posting on the right page. Am restoring my Dommi 88 & find excessive end play on the main shaft ( approx 1mm ). I have done the following:
Shrunk fit new bearings all round
Replaced all PB bushes
Gasket thickness is correct on the inner cover
Bolted on the clutch centre but no difference in play
Cant figure out what could be the problem as there are no washers, bushing collars etc in the assembly.
Any help would be very welcome as work has come to a standstil
Thanks
Anji
Pune, India
 
Anji, I believe that the nut on the end of the main shaft locks it in place with the bearing that is in the inner cover on the R-hand side of the box, are you sure that this bearing is not moving with the shaft in it's seat?
 
dave M said:
Anji, I believe that the nut on the end of the main shaft locks it in place with the bearing that is in the inner cover on the R-hand side of the box, are you sure that this bearing is not moving with the shaft in it's seat?
Click to expand...
Hi Dave
Thanks for replying. No, the bearing is definitely not moving & also I had shrunk fit it in the inner cover. It's the main shaft that is moving in the bearing. tightening up the clutch inner onto main shaft does not resolve the problem. The assembly is as per the manual & exactly the reverse of dismantling.
Can't figure it out
Anji
 
Anji, I have just looked at a Commando gearbox and a separate main shaft in my workshop and the main shaft is locked into the bearing by the nut that sits under the clutch actuating mechanism, it is impossible for this shaft to move at all unless the nut is missing, or has refused to tighten all the way due to a burr on the thread, or the bearing is moving, I suggest that you remove the ring nut that holds the clutch mechanism in the inner case and see if you can spot what is moving. Heating the case to insert a bearing doesn't guarantee that the interference fit between the case and the bearing is a good one, some one may have beaten it out cold with a hammer and drift earlier in it's life.

By the way I have just returned from the Cartier show in Hyderabad, there was a fine array of machinery there including several Nortons.
 
dave M said:
Anji, I have just looked at a Commando gearbox and a separate main shaft in my workshop and the main shaft is locked into the bearing by the nut that sits under the clutch actuating mechanism, it is impossible for this shaft to move at all unless the nut is missing, or has refused to tighten all the way due to a burr on the thread, or the bearing is moving, I suggest that you remove the ring nut that holds the clutch mechanism in the inner case and see if you can spot what is moving. Heating the case to insert a bearing doesn't guarantee that the interference fit between the case and the bearing is a good one, some one may have beaten it out cold with a hammer and drift earlier in it's life.

By the way I have just returned from the Cartier show in Hyderabad, there was a fine array of machinery there including several Nortons.
Click to expand...

Hi Dave
Couldn't make it to Hyderabad this time. Pity, would have loved to have met up with you. Maybe next time
Reg the g/box, it's off the bike & the float is definitely there. The thread is clear & I can see the shaft movement in the bearing.
Another query, Dave. This is the first AMC box I've worked on. What is the correct position of the slots on the cam plate at time of assembly with the claw facing the upper right stud. I've done a mock assembly as per the manual, but cannot select gears ??
I had an ES2 500 which I sold recently & also an Inter 500 plunger which is next up for restoration. Also have. a Sq
4 , BSA Super Rocket which I rode back to India from UK in 1965, Guzzi Falcone etc. Currently also restoring a 1921 Sunbeam.
Anji
 
Do a google search for www.classicbike.biz there are copies of Workshop and parts manuals for Triumphs and Nortons online. I seem to remember that the upper arm of the quadrant (the bit that the barrel with the hole fits into) is supposed to be in line with the closest inner cover stud and the selector is supposed to have it's detent plunger engaging the final slot going anti-clockwise, In practice I always assemble this selector mechanism without any gears or shafts first as the quadrant upper arm sometimes fouls the inner case and either requires a little bit of filing of the case or else retiming by one cog. I then make sure it can comfortably go into each detent with the inner case in place.
 
dave M said:
Anji, I have just looked at a Commando gearbox and a separate main shaft in my workshop and the main shaft is locked into the bearing by the nut that sits under the clutch actuating mechanism, it is impossible for this shaft to move at all unless the nut is missing, or has refused to tighten all the way due to a burr on the thread, or the bearing is moving, I suggest that you remove the ring nut that holds the clutch mechanism in the inner case and see if you can spot what is moving. Heating the case to insert a bearing doesn't guarantee that the interference fit between the case and the bearing is a good one, some one may have beaten it out cold with a hammer and drift earlier in it's life.

By the way I have just returned from the Cartier show in Hyderabad, there was a fine array of machinery there including several Nortons.
Click to expand...
Hi Dave.
A friend of mine with a Fastback found the mainshaft nut in place but not tighten because there was no thread more.
The mainshaft mooved a lot and so had broken the first layshaft gear.
Piero
 
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