countershaft question

motoddrob

motoddrob

Hero member
Location
S/W Australia
Just installing the countershaft back into the lower case, have replaced the bearings. With the r/h side bearing sitting hard up in it's housing, and the l/h outer race hard up against the retaining screw, I have sideways play on the shaft. Pushing the l/h bearing outer race hard up against the inner race eliminates the sideways movement of the shaft but leaves a 0.7mm gap on that retaining screw. Both bearing inner races have no play between the circlip and shim.
Any idea what's going on??
Cheers

Just fitted a spare countershaft I have, samething, either sideways movement or gap between housings
 
I've run across several engines that used a shim between the right side bearing and the case. I've also seen different size shims residing just behind the retaining clip that keeps the inner bearing race onto the shaft. If you are still using the same shaft as before and have only changes the bearings compare the new ones with old and see what 'ya got. 

Tom
 
More learned than I there are but how do the gears line up with the layshaft?
0,7mm doesn't sound much once you take into account heat expansion.
Ciao
Paul
 
I used a puller to pull the bearings back hard up against the shim/circlip, gained a total of .5mm so now it feels good. Just need to remove those pesky studs before I can move forward!!
 
Some 500's ive seen inside used shims on the countershaft to contol end float, they sat between the outer race of the bearing & the cranckcase casting on the "output" end...

Ross.
 
Rob,

0.5mm sideways play is just about perfect, shouldn't be less than maybe 0.3mm, no more than 0.7mm.  Shims can be placed on the "outside" of the RH bearing, between outer race and crankcase.  Easier than spacing out the inner race which needs to be removed to adjust.

While you're at it, check the gears for 2nd and 3rd on both shafts.  When either is engaged, clearance btween 2nd mainshaft and 3rd countershaft can get awfully close, allowing the wrong gears to mesh/rub slightly.  Clearance can be maximised by flipping over the countershaft 3rd gear, it is flat on one side and has a small abutment on the other.  Also check the selector forks have play when each of the gears are engaged.

piet
 
You may find this of help. The engineering drawings from the 750 SF1 hand book. as the gear boxes have not substantially changed I think the clearance figures are transferable. For the Lay shaft from the fixed teeth to the RH side (last gear box pix on P47 original book) the Max Play is 0.500mm, so I would aim for 0.200-0.300mm The parts list shows the Shim washer (20) on the inside of the shaft and a Washer (18) next to the circlip at the end of the shaft. Both small lands on the gears are shown to the right. I am with Rob on all the checks. The main figurer that is missing is the clearance between the gearbox shift fingers and the slots throw gears. Still looking for the them.

(I can't make the PDF small enough to be clear and still attach here e-mail me if you want a copy)

JugsS
 
Jugs_S said:
You may find this of help. The engineering drawings from the 750 SF1 hand book. as the gear boxes have not substantially changed I think the clearance figures are transferable. For the Lay shaft from the fixed teeth to the RH side (last gear box pix on P47 original book) the Max Play is 0.500mm, so I would aim for 0.200-0.300mm The parts list shows the Shim washer (20) on the inside of the shaft and a Washer (18) next to the circlip at the end of the shaft. Both small lands on the gears are shown to the right. I am with Rob on all the checks. The main figurer that is missing is the clearance between the gearbox shift fingers and the slots throw gears. Still looking for the them.
Click to expand...

You won't find them, I'm afraid.

It is important they don't place pressure on any of the gears while engaged.  They need to be loose when each gear is selected.  The engaged gear also needs to be able to move freely in axial direction.  If this cannot be attained with the selector forks in their current positions, the 2 smaller ones can be swapped around.  No more than 0.1mm needed, but this is quite crucial for smooth changes and and reduced friction/wear within the box.

To attain clearance between opposing 3rd and 4th gears (my mistake in previous post!), it may be necessary to flip over the 4th layshaft gear, regardless of where the land ends up.

I have found it is better to err on the loose side than to close up clearances on the gear box shafts as far as possible.  Leaves the selector forks more room to move about without fouling the selector slots.

piet

 
I got the end play down to 0.2mm. Manually going through all the gears it's changing quite smoothly. Pretty sure I got it right. Didn't turn any of the gears around.
The initial problem was that I had the bearings pressed on too far. Pulled them back to the shim, still with enough clearance to turn the shim with the fingers.
Anyway the bottom end is now zipped up, never to be seen again in my lifetime I hope!!
 
sfcpiet said:
To attain clearance between opposing 3rd and 4th gears (my mistake in previous post!), it may be necessary to flip over the 4th layshaft gear, regardless of where the land ends up.

I have found it is better to err on the loose side than to close up clearances on the gear box shafts as far as possible.  Leaves the selector forks more room to move about without fouling the selector slots.

piet
Click to expand...

I have installed the transmission and done a lot of test shifting.  I have noticed that the mainshaft 3rd and countershaft 4th gears are extremely close when 4th is engaged.  I have 0.4mm axial play on the countershaft, so the mainshaft 3rd and countershaft 4t don't seem to be interfering with each other.  Do I need to flip the countershaft 4th gear to provide some minimum clearance in spite of there being no apparent interference?

Chris
 
Chris,

If the gears don't contact, all should be ok.

Give the mainshaft all the play that the current spacing allows by pushing it home in both directions to have the outer roller races hard up against the case.  Check if the gears mesh correctly without any others interfering and the selector forks have clearance when each gear is engaged.

If you're uneasy with the clearance between the 3rd MS and 4th LS, you can flip over the 4th gear, doesn't do any harm, may look a bit strange though.  A slight offset between 4th MS and LS may result.

piet
 
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