Laydown gearbox

I don't know about the GT 100 prefix but the GT 101 is for use in pre Featherbed frames singles and the GT 102 is, designated for pre Featherbed twins. There are a few differences like the mainshaft lengths and apparently the kickstart shaft is longer in the case of singles. I'm still trying to find out about differences in gear ratios from box to box though.

Hope this is of some help Keith

In the Technical/singles/gearbox section of this website you will find the information you seek. George Cohen has a reprint of data from a 1987 copy of 'Roadholder which gives all the gear details for Normal, Close and Wide Ratio boxes. His Norton Website is a useful source of information

Do not despair. I understand that all main gearbox shells from 1948 to 1956, i.e. the laydown box, are identified as GT100VAF. Top mounting lug widths seem to vary, 3 5/16'' top lugs, 3 7/16'' bottom, or 3 5/16 top and bottom. the extra bottom width is on the chain case side. machining of the surplus or shimming excess clearance is easy. Single boxes have a shorter mainshaft,8 5/8'' whilst twins use an 8 11/16'' mainshaft. These are interchangeable and available. As a result of this difference in length, the twin mainshaft protrudes from the sleeve gear showing a gap before the clutch splines, the single mainshaft does not.

Hope that this helps,good luck.

That's interesting. Does the International use the 'single' or the 'twin' gearbox mainshaft in a horizontal box? There's only 1/16" in it, mind.

Paul

Previously Charles Bovington wrote:

Do not despair. I understand that all main gearbox shells from 1948 to 1956, i.e. the laydown box, are identified as GT100VAF. Top mounting lug widths seem to vary, 3 5/16'' top lugs, 3 7/16'' bottom, or 3 5/16 top and bottom. the extra bottom width is on the chain case side. machining of the surplus or shimming excess clearance is easy. Single boxes have a shorter mainshaft,8 5/8'' whilst twins use an 8 11/16'' mainshaft. These are interchangeable and available. As a result of this difference in length, the twin mainshaft protrudes from the sleeve gear showing a gap before the clutch splines, the single mainshaft does not.

Hope that this helps,good luck.

I have a Laydown gearbox with GB8 6543, it looks in very good nick, the mainshaft and general condition and I was thinking of using it with a 99 engine I have, without getting oily that the only obvious number I can see!

Cheers

John H