SOLD – BSA ZB31 gearbox M20 M21 B33 rigid and plunger frame models.

SOLD – BSA ZB31 gearbox M20 M21 B33 rigid and plunger frame models.


BSA ZB31 gearbox. Gears turn and cases included. M20, M21. B33 rigid and plunger frame models.

I have shown the 3 main elements. The gears all turn freely and you can see they are used, but in good condition.

The outer cover has a small amount of corrosion on one part (shown) with part of a fixing inside the hole.

The main case is in good condition, but items will need to be freed up.

The clutch adjuster on the inner case top is broken, as usual. It will need a weld repair.

You will need to get some studs and nuts for the covers as what you see is what you get.

Part numbers for you to make sure you’re buying the right gearbox for your needs:

  • Main case 66-3123
  • Inner cover 66-3129
  • Outer cover 66-3126


International shipping available.

Viewing: Please come and check it over before you buy. It is at PE28, near St Ives in Cambridgeshire.

Shipping: I usually ship to most destinations. If you don’t see a price, please ask. Thanks. International shipping available.

Collection: If you don’t want it shipped, I have plenty of space. If you can’t collect for a while, it’s not a problem. However, I will need to be paid very soon after the sale. Thanks.

Payment: Good old fashioned money on collection is preferred. I can accept payment through PayPal or by bank transfer as well.

Import Taxes: Please note that IMPORT DUTIES are not something I can control. If you are buying from outside the UK, there is a chance that you will have to pay import taxes. Import taxes vary from country to country. If there are charges to pay, it is the buyer’s responsibility to research the cost and pay the duties. The price that you see on my advert is for the item and not the item plus whatever taxes might be due.

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