Early B33 (1947)

[MGI]

No Mate, It's a bitza - The primary chain case is the later aluminium type, the foot rest brackets have been changed to suit, have now discovered the dynamo isn't charging! Could be a problem as electric starting tends to knock the battery about a bit but fortunately there is a charging plug connected directly to the battery and located in an accessible position just tucked ion under the seat. Gives me a breathing space. There was a slight problem when a crankcase breather was discovered between the primary chaincase and the crankcase just where the gubbins for the starter motor needs to be located. Went out on it yesterday, did about 80 miles (forgot to check the speedo prior to departure) and everything was good apart from an oil leak which has materialised somewhere in the head area.

[idie]

Interesting that you have the later case fitted. If you ave Pearsons electric starter. The smallest engine sprocket is a 21 which is 2 teeth higher than standard. You will need to drop the size of gearbox sprocket then the speedo will run fast as the layshaft that drives the speedo will spin faster so the speedo will need re-calibrating. Have played this game.

[MGI]

The speedo is a reconditiponed unit and when it was fitted to the bike the engine sprocket had 22 teeth. It was very high geared which was actually only noticeable when starting off. It seemed quite happy at 70 and strange to relate, when I took it out yesterday it cruised along at 70 and sounded sweet and unstressed. Having said that, and read your post, it was probably doing quite a bit less than 70 given that one tooth difference on the engine sprocket is equal to 2 teeth on the rear sprocket! (I believe)

[idie]

If you have a Pearson electric start the engine sprocket will be a double one. One for the primary drive and a narrow one for the starter drive. Your indicated speed was most likely correct as engine sprocket size will not alter the speedo. Only changing the gearbox sprocket or that on the rear wheel will alter the speedo reading.

[MGI]

You are correct Idie, although the sprockets are not double as in joined together, but there are two of them and the inner one connects to a secondary sprocket which then drives a shaft through the centre of the inner chain case where there is another sprocket which then drives the starter motor which is located under the engine/gearbox ass. It was a surprise to me as I was under the impression that the starter motor was inside the chaincase. A cautionary note is that because the starter protrudes below the bottom of the engine, care is required when loading the bike into a van - we had to physically lift the back end to avoid scraping/knocking the said motor where the ramp met the floor of the van!. Thank you for pointing out that changing the front sprocket does not affect the speedo calibration as I had imagined.