On Sunday I returned home from a rally in 3rd gear, a fairly common occurance with an M20

This is the larger of the 2 gearbox selector springs, but it got me wondering how common this is and whether its always the larger spring?

email (option): robmiller11@yahoo.co.uk

Is that the one that Henk broke in Normandy ?

Gearchange springs seem to be problematical. Nortons do it to :-



This is the lever return spring but the pawl springs fail too. I always carry a spare in my Commando tool kit.

Is this something we should consider making?

email (option): Britool51@hotmail.com

Available from usual outlets, russels @ draganfly

Part of my std bsa ride out kit !!

A bit like amex, i dont leave home without both springs in my pack

Other credit cards are available

:-)

Jo'b

email (option): Jonnyob1@googlemail.com

It's interesting to speculate why these gearbox springs break. Is it rust? Well they do live in an un-oiled space so must be subject to the rust worm, but Rob's spring doesn't look very rusty. Is it metal fatigue? Well it could be, but considering that valve springs operate thousands of times per mile whereas gear change springs operate maybe a dozen times per mile, surely valve springs should break much more frequently but in practice that's virtually unheard of. It sounds to me like the springs were badly designed - either using inappropriate materials or carrying too high stress levels - although this would be very unusual for a company like BSA which had access to excellent engineering skills. Is it all down to the low quality of repro parts? Did gear change springs break regularly in the 40's and 50's?

ChrisJ

Breaking of the larger spring is unusual..it is generally the smaller one that goes. That is the one that Henk broke in Normandy.(though he had never broken one previously) Sudden difficulty changing gear or being stuck in just one gear are the 'giveaway' symtoms of this problem.
Rust can be a problem, also the spring rubbing on the back of the ratchet assembly components over a period of time.
Failure of either spring is a rare occurence..but I always say that everyone will probably break ONE if they have an M20 long enough.
In 30 years or more and over hundreds of thousands of miles I have had one fail...
I would recommend that everyone carries a spare as part of their touring kit..it is not a difficult job to do if required. Though you may never use it, if the day does come you'll be glad you have it!!.(Henk was glad I had one! )...Ian

email (option): ian@wright52.plus.com

It would appear from the lack of responce to my poll that this isn't as common a problem as I thought, and a pretty amazing coincidence that Henk and I both broke one within 2 weeks

email (option): robmiller11@yahoo.co.uk