Gearbox bearing clearances

I'm rebuilding my gearbox and at the point of assessing the mainshaft and layshaft.

The workship manual gives spec.s for the i.d.s of the various bushes and of the rolling element bearings but not for the corresponding diameters on the shafts.

Does anyone have information on the latter, or alternatively of the allowed clearances?

My micrometer measurements of my shafts imply clearances between 0.0015" and 0.0035" for the bushes, and 0.0003' and 0.0005" for the inner races of the bearings. Are these reasonable?

Also, the list of bushes includes a "layshaft bush" not further identified. Elimination suggests this must be part 04.0146, the bush within the kickstart shaft 04.0477 (items 18 and 17 in the Group 6 drawing in the parts book). I'd be glad if someone would confirm this.

JulianWells said:

Also, the list of bushes includes a "layshaft bush" not further identified.

Click to expand...

040146 is usually described in factory parts lists as "Bush, Shaft" or "Bush".

JulianWells said:

Elimination suggests this must be part 04.0146, the bush within the kickstart shaft 04.0477 (items 18 and 17 in the Group 6 drawing in the parts book). I'd be glad if someone would confirm this.

Click to expand...

One main and two layshaft bushes:

Two sleeve gear.
Either:

Or:

L.A.B. said:

040146 is usually described in factory parts lists as "Bush, Shaft" or "Bush".

Click to expand...

Indeed; the question is whether this is the bush that is meant by this rather laconic term in the Technical Data section of the manual.

Fortunately it turns out that AN are rather more specific:

JulianWells said:

Indeed; the question is whether this is the bush that is meant by this rather laconic term in the Technical Data section of the manual.

Click to expand...

Yes, as the "Layshaft third gear bush" and "Layshaft first gear bush" are listed individually in the manual technical section then "Layshaft bush" has to be the bush inside the kickstart shaft as there's no other layshaft bush.

The workship manual gives spec.s for the i.d.s of the various bushes and of the rolling element bearings but not for the corresponding diameters on the shafts.

Does anyone have information on the latter, or alternatively of the allowed clearances?

Click to expand...

In the recent thread for combat specs, Matinatlas posted the link to the Norton Service Release N3/73, which includes diameters for mainshaft and layshaft on the Technical Data page; although the Release is for the 850 Stage 1 Performance Modifications, the Tech page (page 5) lists the engine capacity at 745cc (73mm bore).
See article here: