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Jubilee M/shaft 3rd gear Chamfer or not?


Hiya - Could the more knowledgeable amongst us advise please? I have sourced a replacement main shaft 3rd gear, it all checks out dimensionally and it fits the splines. However, as you can see from the pic there is no chamfer on the new part. What are the merits of chamfering? Could I leave it unchamfered? 

Thanks in advance Gary


Hi Gary - there were several changes to these gears down the years (in the so called early gearbox), and its best to keep the gear sets together. To answer your question fully, I would also need to see your sleeve gear (the one left inside the gearbox) and the other side of the two gears you show.

An engine number will help me as well.


Andy S


Two points

1) You did not show me the other side of both of the gears - the chamfered one & its mate. Ideally, I'd loke to see a sideways on foto, so I can see front & rear at the same time.

2) From the foto you sent looking into the gearbox, I can see that you are a) lucky and b) have a job to do.

2a) You are lucky in that the bush to the left of the sleeve gear does not appear to have come loose. They very often do come loose, spin in (& RUIN!) the crankcase.

2b) What you need to do, & you may need to enlist help in this, is to check that the bush has not moved in the first place - use a bit of wire (straighten out a paper clip) and chack that the oilway above is still in line eith the bush - can you poke the wire right through? Then you need to pin it in place to prevent ANY chance of it moving in the future. This was done on all Electra, plus Jubilees & Navigators AFTER Eng No 106838 - hence I asked or your engine number.

See the photo attached to show what I mean - Layshaft bush pinned to prevent rotation.



Many Thanks Andy - If you look closely at the layshaft bush you will see where I scribed a line with a centre square so I could line up with the oil way. The bush wasn't loose but wasn't exactly tight either, so I dimpled it and used bearing lock. I might still pin it after reading what you have said. In regard to the new pics, there is some colour on the original 3rd gear that it just DPI Developer, I thought if I had to re-use it I could gain some confidence by doing NDT, it looks ok, so it's a plan B if new gear is a no goer. 





Yes, if you can, peg the bush for piece of mind!

The two gears you showed me (one chamfered, and one not) are interchangeable on the Mainshaft only, as the have undercut 'dogs' on the reverse side. My preference would be to use the non-chamfered one. There is a similar looking gear, chamfered, that is used on the Layshaft, BUT it has rounded pegs on the reverse side, that match the holes on the 1st (starter) gear.

See my sketches attached. (You have also Identified a 4th gear for me - a chamfered mainshaft selector gear - thanx). You CANNOT use it on the layshaft!

Just to scare you into pegging the layshaft bush in place, my 2nd picture is of what can happen if the bush should rotate - you have been warned! (The notes also advise about re-positioning the engine breather - a useful mod if the cases are apart).


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