Layshaft part number

Iâm no gearbox expert but I think I would rely on known quality and use Andover or RGM

https://www.rgmnorton.co.uk/buy/layshaft-all-amc-norton-boxes_599.htm

Failing that, Norvil

dan

In the 1957 spare parts book for the Models 77,88 and 99 the main shaft part number is 040001. It is the same for all these models and it is the later Norton/AMC gearbox and not the laydown gearbox. I have the spare parts book for the Model 77 up to 1959.

There is also RGM Motors who can supply all the gearbox parts that you will need.

Sorry George I thought yours was an amc box, donât know why.... should have read the post properly!

According to the RGM description it looks as if the shaft should fit both Laydown & AMC boxes. They all evolved from the same origin and there is some interchangeability.

SUITABLE FOR ALL FOUR SPEED NORTON AND AMC GEARBOXES WITH KICKSTART. ie FITS COMMANDO, ALL SINGLES, ALL HEAVY TWINS

A phone call to RGM should confirm this.

Ian McD

Interestingly Andover list a layshaft for the amc box but not the laydown, which infers they donât think they are the same? I too would call RGM they will always refund if itâs wrong.

Fingers crossed!

Etrange les gars, à ma connaissance un arbre de monocylindre type ES2 n'a pas la même longueur qu' un arbre pour un twin type model 7, bien sur la boite G102 est la même est il va rentrer dedans mais il n' aura pas la bonne longueur  pour atteindre l' embrayage au niveau du carter de transmission primaire. Dite moi si je me trompe.  

Heu...je parlais du mainshaft .

I have the GB 8 gearbox from my 1953 Model 88 apart on the bench at present.

Layshaft is numbered N 8031 which is the same used in upright and G101 and G 102 laydown gearboxes. AMC layshaft is not numbered but looks interchangeable.  Same overall length and spline length and gears slide on.

Mainshaft is numbered GT 165 which is the same as a Model 7 lay down box.

My understanding is that the twins have a different mainshaft length from singles.  I think the singles (including International) have GT 165, and twins GT something, possibly 175.  I used to know but.... 

Paul

Conventional wisdom is that the singles mainshafts are shorter than the twins. This appears logical as the twins crankcases are almost certainly wider than the singles. However, I now suspect that the frame also plays a part in determining the mainshaft length. In a swingarm frame the primary cases sit outboard of the rear frame loop. Measuring the position of the inner primary case relative to the seat downtube on a rigid (1937 CS1) and swingarm (1956 19S) reveals a difference of approximately 10mm. To me this suggests a longer mainshaft is required on the swing arm models. When I checked the mainshaft ID in my spare G102 box (possibly for Dan but I can't find the email now) it was a "twins" mainshaft. The box was removed from a 1956 Model 50 and I am sure it was original, the primary was intact and lined up OK.

Just my observations, could be wrong.

Ian McD