Dear all,
It is fascinating how a Lightweight can always find new ways to challenge and frustrate you no matter how often you have rebuilt one! Having had a highly reputable precision engineering company replace my late gearbox bronze bushes and mainshaft bearings with new items from the NOC shop we discovered that the lay shaft was too tight a fit in the crank case end pegged bush. Having searched high and low for a suitable hand reamer that could ream the 'blind' bush and failed I had them ease the lay shaft by 1 thou" so it was a play free fit.
With the correctly assembled gearcluster in place everything runs freely but when I fit the off side gearbox end plate the gearbox tightens up so much the sleeve gear is difficult to turn. The main shaft rotates freely and the kickstart operates it without any binding so I am pretty certain that it is the lay shaft that is running tight in the crankcase end bush. I have checked the lay shaft fit in the kickstart end new bronze bush and it runs very freely. I can only assume that the new crankcase bush 'shrank' a few thou when it was pressed in and my options are to ream it out a few thou or skim the lay shaft a similar amount.
Has anyone experienced this problem before and if so how did you solve it? Is there anything else I might have missed in assembling the gearbox? I have read my original Maintenance manual and the later publication and am pretty certain I am assembling it correctly.
Standing by for words of collective wisdom!
Nick
Check layshaft
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Sage advice as always Peter,…
Sage advice as always Peter, I will find some time later today to go and assemble the gearbox as you suggest and see if the new layshaft crankcase bush is the cause, I haven't replaced the kickstart bush so it can't be that end that is responsible. If the crankcase bush is the problem can you or anyone else suggest a tool or practical way of 'easing' it by a few thou to restore the end float? Having meticulously assembled the rest of the engine with new bearings and gaskets at considerible expense I am loath to strip it all down again!!!! Would an alternative be to ease the kickstart bush which is easily accessible?
Don't you love Lightweights!!! Thanks for all the help. Nic
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Layshaft bush - later gearbox
Hi Nick,
1) does the layshaft, on its own, spin freely in the new bush?
2) try Peters trick of just fitting the mainshaft (to keep everything stable), plus the layshaft with 1st & 4th gears into the inner cover with the kickstarter in place.
3) does it spin freely before you nip it up, or does it nip up as you tighten the nuts.
- If its already tight before you nip things up - a slight misalignment has occured. Engineers blue will be required to find out what is rubbing
- It it nips up as you tighten the coner down, its most likely the thrust faces (as Peter suggests) are slightly proud.
If its the latter case, supply a dimension/drawing of how your bushes look, and I'll compare to one here, that I have prepared earlier. Cheers
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Hi Andy, Apologies for the…
Hi Andy,
Apologies for the delay in my reply but Easter is always a mighty busy time for me! I have had another session following Peter and your advice and found the following.
- The new layshaft bush supplied by the NOC shop and fitted, pinned and drilled by Hamlin's engineering in Bridgewater definitely shrank when they pressed it by a couple of thou' because the original layshaft was almost an interference fit and I have had to ease it by 2 thou for it it to spin freely when inserted.
- They replaced the gearbox main bearing and that rotates freely with the sleave gear inserted.
- I have replaced the kickstart side main shaft roller bearing which is revolving freely.
- With the 4th gear / sleave gear and mainshaft inserted they all reveolve freely.
- With the 4th gear, mainshaft, layshaft and 1st gear fitted and end plate in place everything revolves freely until the end plate is almost hard up against it's mounts when the main shaft continues to revolve freely but the sleeve gear will revolve freely for about 180 degrees but then tighten slightly. It will still turn but is obviously binding slightly for 180 degrees then frees of completely again.
This afternoon I will try assembling the whole gearbox and tightening it down to see what results that gives! All very frustrating because if the bush is out of line logic suggests it would nip up evenly....and it would do the same thing if the shoulder of the bush is slightly too thick......
Any thoughts, suggestions of how to measure or ease the thickness of the bush in situe without stripping the whole engine down again would be greatfully received!
Confused of Somerset!
Nick
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Thickness of 1st gear on layshaft.
Hi Nick,
Thanks for providing a detailed description of what you have done.
Layshaft jams as gearbox endplate squeezes layshaft with 1st and 4th pinions fitted.
My fix for this was to file a few thou off the flat exposed shoulder of the kickstart bush. It is brassy in colour. Fairly easily filed. No engine stripping required. Bush can be kept in gearbox endplate. Keep any radius or chamfer between bore and flat face of bush. It is there to ensure any radius between shaft and shoulder of kickstart shaft sits in the chamfer. This sort of detail, if ignored, can lead to a jammed layshaft.
My experience as stated earlier came about when I made a replacement kickstart bush and the shoulder was too thick by a few thou. I also noted 5 thou difference in thickness between two 1st gear layshaft pinions. One jammed the layshaft, one didn't. Tolerances!!
I'm sure you will have it sorted soon.
Peter
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Late Navigator Gearbox Blues cured!
Hi all,
Well it has taken 10 months and the very kind advice, wisdom and help of Peter Holland to solve my new layshaft bush binding problem. All that was required was a cleverly designed but very simple reamer kept in line through the kickstart bush in the outer gearbox cover. 5 minutes of careful, light reaming had the layshaft running smoothly in the new layshaft bush. Half an hour later I had the gearbox back together, running smoothly and selecting all four gears - Huzzzzah!!!! A photo is attached.
A huge, huge thank you to Peter who gives so generously of his time, experience and expertise to fellow Leightweight owners. He personifies everything the Norton Owners club and particularly the Leightwight owners community is all about. If anyone has this layshaft bush problem in the future feel free to contact me and I will provide a more detailed explanation of how to solve it.
Off to the garage to crack on with the Navigator rebuild - fingers crossed I can find the time between work to get it back on the road by Easter!
Nick
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Hello Nick,
I had a problem like this. Eventually I found it was of my own making.
Are you reasonably sure the gear selector is in neutral position when securing the gearbox end plate into position. You can get gear dogs hitting gear dogs if one of the gears is selected. Best fix for this is to rotate the sleeve gear as you tighten the gearbox end plate.
You have tried the layshaft into the crankcase bush and it rotates freely? They do shrink fractionally when pressed into the hole.
I doubt the above is your problem.
I solved my layshaft problem by just putting 1st and 4th gears on the layshaft. Re-assemble rest of gear cluster and insert. Now turn the sleeve gear as you tighten the gearbox end plate.
If the sleeve gear gets difficult or impossible to turn, the layshaft endfloat is actually a nip.
In my case a self made replacement kick start shaft bush had too thick a shoulder. Thinning it restored endfloat.
The layshaft is held between the shoulder of the crankcase bush and the shoulder of the kickstart bush. If either bush is not fully home, or the shoulders are too thick, the layshaft can get nipped up.
Be cautious.
Peter