Valve springs

[dukeminor1971]

I've just bought a recently rebuilt 12g295 cylinder head (off a 998 mini) which I'm going to fit to my MM 948. I've read that it's better to have single valve springs fitted (best for the 948 camshaft). The head has double valve springs fitted. If I just use the larger outer springs are these the same as standard single springs?

[philthehill]

Some information so as you can make up your mind as to whether you discard the inner spring or not:-

The single standard valve spring (Pt No: AEA311) for the 998cc Mini is rated at 88lb at 0.973" (compressed check length).

The double valve springs of the 12G295 head are rated at:-

Inner Pt No: AEA401...………..30lb at 0.847" (compressed check length)

Outer Pt No: AEA311...………...88lb at 0.973" (compressed check length)

The valves fitted to the 12G295 head are larger so are heavier than those fitted to the 998cc Mini so I would suggest you do require the extra 30lb.

By all means try the standard single outer valve springs but I would recommend that you keep both inner and outer springs.

Again if you use only the single outer spring remember to remove the inner valve seat collar/seat.

The extra 30lb is not going to make a great deal of difference to the camshaft providing you have good oil pressure.

If you were going to fit heavy duty springs with a rating of 134lb it would be a different matter.

Phil

[dukeminor1971]

Thanks for a very comprehensive answer and for saving me an extra job..