This listing is for a pair of the plain Phospher Bronze bush's to replace the original steel bushes that were pressed into the front and rear selector mechanism plates on the positive stop mechanism on all Norton upright gearboxs between 1934 - 1950 (i.e. the pre-war Dollshead type, as well as the upright enclosed front cover type that were fitted on all roadgoing postwar single cylinder models Post-war from 1946-@51).
Original bushes are often badly worn - recognisable by the gearlever flopping around when you move it - and is a major factor leading to imprecise and vague gearchange. Replacing the original worn (steel) bushes with these new phospher bronze CNC manufactured bearings will make that gearchange more precise.
Price is for a pair of bearings (one front, one rear).
Fitting Notes:
These are CNC manufactured phosphor bronze bushes, and as part of the setup for these, we took a good condition original (upright type) Norton gearbox outer cover with complete gearlever Positive Stop mechanism untouched for many years - in very original condition, with original bushes still fitted (and fyi - original bearings were manufactured in steel).
We did this, so we could ensure that the pressed steel plates that hold the bushes were in good original condition - and therefore accurately machine the new bronze bearings, so we know they would be an accurate 'press fit' into unblemished original plates. We also wanted to ensure that once the new bushes are pressed in (i.e. an interference fit into the front and rear plates) - the internal bore diameter would be of a good/close fit diameter to the original specification, and should not require further honing or reamering.
Therefore providing your original selector mechanism spindles are not overly worn, and your front and rear plates have not been had the old bearings spinning in them to such a degree where the interference fit has worn - then these should fit in with the original interference fit (and are machined with a slight chamfer on the side that presses in, for this purpose) - and should once fitted be a nice close fit to the two spindles.
A couple of hints when removing and fitting new bushes to the pressed steel plates:
- the old bearings can be easily tapped out using a suitable drift
- make sure all parts are cleaned thoroughly before fitting the new bushes
- when fitting the new bushes, place the pressed steel plates on a clean flat and hard surface - i..e a steel or alloy block no a workbench
- Use a soft alloy drift with a mallet to press the new bearings in, to avoid burring the edge of hte bush, and to ensure they go in level
- the gearlever spindle and rear spindle may have burr's from previous wear - ensure these are removed before pushing on the new bushes/plates on to the spindles
- Dry assemble first and if the new bush is stiff on the shaft, it can be hand scraped (with a bearing scraper) or reamer, until it is a smoothly turning fit.
Fully assemble all positive stop mechanism parts with good quality high melting point grease - one of the accompanyning photographs shows an original pre-war Manx gearbox, with the top Dollshead cover removed . . . and this looks like it still has the original 80 year old grease still in place - and look how much they used!
And in the same Gearbox section as these are listed, you will also find new versions of the positive stop spring (which often wears - adding to the sloppiness) as well as the shim fitted between the two positive stop spindles - all useful fitments in revitilising the gearchange when servicing your upright gearbox.
Final point on this type of upright gearbox - there was a deep cylindrical felt seal fitted behind the rear bush on the positive stop mechanicsm on this type of gearbox. We are currently trying to get this orgiinal felt design manufactured - email at sales@racingvincent.co.uk if requiring these, for an update.
Update August 2022 - Please Read Before Ordering: Recently a customer who purchased these bearings came back to me to say, his 'Kidney' shaped pre-war cover would not fit over the front bearing?? I confess I was suprised - as our bearings was copied from an original item from a similar pre-war gearbox . . . and which was checked against multiple gearboxs in my own collection. However - having checked all my own covers - I too found one loose cover, shown on the right in the 4th photograph - with a similar small hole. Having looked at loads of these covers over 40 years I had never realised there was a type with a smaller hole, still learning!! I am not sure why some covers had a smaller hole - but please check your cover before ordering if similar type to the picture - if yours has the smaller hole, shown on the right - then the front beaaring in this listing will not fit through that hole - so either be prepared to open up the hole (which is a personal choice), or do not order this item. Thx. At some point I will try and find the corresponding mechanism for the small hole cover - email us at sales@racingvincent.co.uk if you are not sure
Laydown Gearbox info: Note that the later Laydown gearbox, that followed the upright gearbox from 1951 onwards, had a similar looking Positive Stop mechanism, but actually the two similar plates fitted to this type did not hold bushes (see last photograph). The bushes for this type were mounted in the 'laydown' inner and outer covers. We do not offer these yet - but see Item 1060 for more information if requiring these
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