Upright Gearbox Movement

the inner faces of the gearbox top lugs wear, and it becomes increasingly difficult to lock it in place.   After a while the wear forces the top lugs to bend inwards, and then they break off.  That is not a good thing.  Better to check it out properly and fix before the problems get serious.

Paul

3 choices,

1. build up with weld and dress back to flat at correct width dimension

2  cut away until flat and add shims to bring width back to correct dimension.

3  cut away an exact amount and drill the holes out again to a set size and add 2 steel top hat bushes that have correct hole diameter for stud and thickness to bring the width back to standard.

2 is fussy and shims can break up, 1 is easiest and brings back to factory dimensions, 3 does same but is non standard but will last longer and cope with abuse.

The previous owner of my Inter made the mod in the picture attached. It seems to have worked for a couple if thousand miles so far.  The lugs are too thick to bend safely. The bush must be a snug fit in the lug.

at the state of the lug on frame and gearbox. A lot depends on how much wear there is.  If it's moderate, you may be able to shim it up.  The modification described by David Cooper looks good to me.

In severe cases of wear, I have heard of people cutting the lug off the frame and fitting a laydown gearbox between engine plates at the top. 

If the gearbox is moving, despite tightening both upper & lower bolts, the lower mounting hole in the box is probably worn. As Paul has said it will eventually lead to failure of the top lugs. I have solved this problem on a Dolls Head box by following the late Dr Cohen's advice on this subject. It involves boring out the lower mount and fitting a steel top hat bush at either side. This can restore both the bolt to hole fit and the fit between the frame rails.

The following is an extract from George Cohen's website:

Dolls head and up-right gear boxes are liable to break the top mounting "ears". This is usually due to a fault at the lower mounting. The lower mounting hole tends to "elongate" in a fore and aft directing as a consequence of the engine trying to pull it forward and the rear wheel attempting to pull it backwards. The bolt also wears. When this happens to a severe degree then the top mounts are put under strain and eventually break. The remedy is ensure a perfect fit of the lower mount. I bore out the "oval" holes and fit bushes which are lined reamed together so that there is a exact 1/2 inch hole (and perpendicular to the frame ). Sometimes "top hat" bushes are required to take up any slack in the transverse dimension. Make a new bottom bolt. The aim is to establish a snug fit of the lower mount.

          Another way....... On some old and shagged out machines, both the ½ inch holes in the gearbox and also in the frame are no longer round. On a bike I was working on last week, these hole were worn and oval and consequently the gearbox could be ‘twisted’ or ‘rocked’ from side to side. My remedy was:

Firstly drill out the worn holes with a 13.5mm bit (13.5 mm = 0.531 inch) in both the frame and the lower mount of the g/box shell. You must do this accurately, so that the new holes are precisely perpendicular. A Bridgeport or similar size mill makes the job easy.  I then skimmed each side of the lower mount of the g/box shell flat and square.

I then took a piece of 9/16th inch (0.562 inch) EN 1A bar and turned it down in the lathe to a diameter of 0.532 inch with either end turned further down to 0.500 inch. I screw cut 26 TPI threads to either end to take the appropriate cycle thread nuts. Then by using a reamer, I reamed all three holes (gearbox and both sides of the frame) out a tad, so that the new bolt was a snug tap fit. With the g/box shell held in place by the new lower mounting bolt, I could see that there was gap on either side to the frame. With the top mounting “ears” in the correct, central place; the gaps at the lower end of the g/box to the inside of the frame was 0.020 inch on one side and 0.032 inch on the other. Make up two appropriate size shims and ‘BOBS YOUR UNCLE’, a perfectly fitting gearbox.

Who did the work for you Mark? I recently posted that the site's "Services" tab could do with a revamp, and this is exactly the sort of thing I think needs including.

https://www.nortonownersclub.org/node/14580

Cheers and congrats!