Sick Engine

[Stuart Giles]

What would cause a valve spring to break?

Material fault
Harmonics
Coil bound
Three amongst a range of options

C

Wouldn't have thought coil binding would have been Henry's problem unless the cam had really radical lift as the Maxi springs have fewer (but thicker wire) coils than the A7 ones. But as apparently Henry's motor was using the A7 valves rather than the longer "A" series ones more commonly used with this setup, the seat pressure and therefore spring preload would be quite high.

Sourced in China, where they sometimes do not know how to temper metal.

Possible that the Seven Workshop etc. A7 springs are amongst the tons of car parts that are Chinese manufactured even when apparently UK sourced. Wouldn't have thought it likely that any of those dusty old boxes of Terry's, Tranco etc. Maxi valve springs that have been and are being used in A7 motors would have been manufactured offshore.

I have experienced apparently random valve spring breakage, but not so far on an A7 motor. Exhibit A m'lud...



Couldn't see any reason for this breakage, but I hadn't built the motor, so it's possible the builder had  re-used the old springs. Fitted new ones checked for binding etc. still running OK 5 years later.