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Mk3 Gearbox Shell Casting Issue

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I had to buy one of the new manufacture Mk3 gearbox shells, as my original was cracked.  I am now at the assembly stage and having fitted the quadrant and camplate, started inserting the gears and am struggling with engaging the mainshaft selector fork with the camplate. I am not new to building gearboxes, having rebuilt my original Mk3 and more recently my Atlas boxes, plus T120 and T140 boxes, and have never had any issues before.

I measured the depth that the selector fork spindle location is recessed in the shell and found that compared to the original shell, the new one is 2,5mm more recessed; i.e. the shell casting is thicker. The effect is that the selector fork contacts the shell before its spigot can engage with the camplate slot.  After much fiddling, I got the fork to finally engage (moving the camplate did not really help), but decided to remove it again and struggled just as much to get it out, even with the layshaft and mainshaft removed.

Has anyone else encountered this issue?

Andy

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Andy:

Have you questioned the supplier about the problem?

Will they take it back?

If the supplier is reluctant to help you out, can you give us the name of the supplier such that we do not patronize that company?

Mike

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The casing is AN product. The only difference between the MK3 casing and the pre MK3 casing relating to this area is the setting of the cam plate and quadrant Bushes. The camplate other than neutral button is no different, the selector forks are the same as pre MK3 also. The selector fork spindle is also no different, nor the machining in the clutch end of the gearbox. 

What part of the selector fork is engaging with the shell? Considering the point of alignment is when the button on the fork is engaged with the plate, it suggests something is seriously amiss. 

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There is a procedure for getting the selector arms in position. It is best to mount the box vertical to help make the job easier.

The Layshaft should have its 3rd & 4th gears added and then it is slipped into its roller bearing. Next add a selector to the Mainshaft 3rd gear and the camplate.

Now add the last two Layshaft gears along with the second selector. Make certain that both selectors have slotted into the camplate. Feed the selector arms rod through each selector. You will probably need to wiggle or move the rod and arms a little in order to get the threaded end to screw into the casing.

Attachment is minimal but does help. 

 


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