LCGB Forums

Hi,

Doing a big update on the Gearbox Visualiser, and wondered if there’s anything to add for the older machines.

I’ll admit I don’t know much about these, so no clue on interchangeability and compatibility.

So any experts (1) know, and (2) want to collaborate?

Thanks, Tony

I'm not an expert either. AFAIK, all you can change is the ring gear and pinion. A lower ratio is used when there is a sidecar fitted.

I've always visualised the gears as, 1st-good, 2nd-good, might give 3rd a go if there's a nice long flat bit of road or a slight downhill coming up. Lol.

As far as I know (and I stand to be corrected), there are three different crownwheel & pinion setups:-

D/LD 150 - Pinion 13 teeth, Crownwheel 45 teeth

D/LD 125 - All models up to the early Mk3 (1957) - Pinion 13 teeth, Crownwheel 46 teeth

LD125 Mk3 (and French LD125 Mk4) - Pinion 12 teeth, Crownwheel 45 teeth

In addition, there is a (rare) crank & clutch bevel setup with 17 teeth on the crank, and 25 teeth on the clutch, in place of the usual 19 teeth on the crank, and 26 teeth on the clutch. (There is also a matching kickstart bevel with 17 teeth - I've got the Mk3 engine set, presumably there's one for the Mk2 150 without the epicyclic kickstart.) This setup was used specifically when fitting a sidecar to the 150 models, before the 12 teeth pinion & 45 tooth crownwheel setup was introduced.

This gives a total of six possible top gear ratios(crank to rear wheel ), which I've calculated as follows:-

With the usual 19/26 teeth crank/clutch bevels

13/45 teeth setup - 4.74:1

13/46 teeth setup - 4.84:1

12/45 teeth setup - 5.13:1

With the 17/25 teeth crank/clutch bevels

13/45 teeth setup - 5.09:1

13/46 teeth setup - 5.20:1

12/45 teeth setup - 5.52:1

Bearing in mind that the standard 4.74:1 ratio can be on the overgeared side, there should be a ratio to suit most applications, although 5.52:1 on 8" wheels is probably undergeared! There's always the option of fitting aftermarket 10" wheels and playing around with the wider range of tyre profiles available.

I also seem to remember that some late 125 machines had different layshaft gears, giving a lower second gear - and an even larger gap betwen 2nd and 3rd......