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Just started looking at the gearbox in my Navigator, its the early type.

There are some shims in the gearbox, see the first photo.

They were fitted as follows.

1- on mainshaft adjacent to sleeve gear.

2- on layshaft, kickstart shaft end.

3- on kickstart shaft.

Is this correct?  I think the shim adjacent to the sleeve gear is doing nothing.  

The two on the layshaft do little, the layshaft has 0.05" end float.

The only shim (washer) I am confident about is number 3 on the kickstart shaft.

As I am going to re-bush the box I am thinking I can reduce the layshaft end float to something much better.

Any thoughts?

The second photo shows why the gearbox leaked so badly!  

 

 

 

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This is the extract from the manual - i don't remember any shims being present but there might be one behind the sleeve gear to deflect oil, or is that in the AMC box?!

Sometimes the box will jump out of 1st, shimming the layshaft helps eradicate that, a search should find the threads on that, but more importantly remember to drill and pin the layshaft bush nearest the sleeve gear, they are prone to turning and ruining cases if the oil level should drop below the recommended level, 

Box

Gear

This might help

https://www.nortonownersclub.org/node/13585

dan 

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Footnote - I’m guessing what you are calling the core plug is the plug over the layshaft end bush? Check that it hasn’t gone as a consequence of damage to the case? 

Dan 

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The National MC Museum have a manual DESCARTES/294 covering the early lightweight gearboxes. Just the gearboxes. This may help. There are potentially a lot of shims in this gearbox. 

The parts list identifies many shims but the exploded diagram does not show them all. By a long shot. 

Memory a bit dim now but I think there are potentially shims on mainshaft bearing, layshaft end float, kick-start end float. Selector face cam shaft end float and position. Maybe some more. 

Think they are covered in the above 4 page manual. 

Try Andy Soch.

Pete

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Thanks for the replies.

The shim I've marked as "1", I think it should gear on the ratchet shaft, it's taken out the end float perfectly.

I have various manuals for the lightweights, not particularly useful I have found.

The link to the other thread very useful, thanks for that.

Today I re-bushed the layshaft first gear and the kickstart shaft.  Then a trial assembly with the shafts and gears in the end plate.  I have shimmed the layshaft 1st gear to ensure full depth of (dog) engagement.

Also checked that there is adequate axial clearance between the gears.

Then I made a dummy D/S layshaft bush, gradually modified the thickness of the "head" until end float became acceptable.  I wonder if the end float here needs to be carefully controlled?  The kick start mech pushes the shaft towards the drive side.

Still plenty of work to do so probably more questions!

In my original post I showed a photo of the core (welch) plug that seals the end of the ratchet shaft.  Looks like someone had tried to hammer it in sideways damaging the case.  I wonder why blind ended bushes were not used rather than the core plug arrangement?

Ducati where very fond of shims.  I rebuilt an early vee-twin, just about every shaft in the engine/gearbox had shims!

 

 

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John, I do wonder if the kick-start seal, which is just an o-ring, would do a much better job if it was squeezed axially. (like an o-ring in a properly sized groove). This means shimming out all kick-start end float and a bit more to squeeze the ring. 

Folklore says they all leak, with some folk putting in two rings. 

It seems a very poor design and I suspect AMC had shims to control axial movement of kick-start shaft. 

Good luck with your rebuild. 

Peter

 

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