3 replies to this topic

[jakejakejake1]

Hi Everyone,

A hopefully straight forward question regarding valve stem wear -

Am I right in thinking the nominal diameter of a valve stem is 0.2795" (279.5 thou)?

If so, what is the acceptable valve stem wear?
I just measured the valve that came out of a supposedly rebuild head (massive play in one valve, had caused a burnt valve seat, guide wear is visible to the eye and huge play in that valve) and I found the minimum diameter to be 277.8 thou, is this too worn for reuse?

I have only got the one valve out so far as it had so much play in it, so am assuming this is the worst case.

Cheers,
Jake

[carbon]

Jake,
Old factory BL manual for 1275 motor gives following dimensions in inches :
Inlet valve stem dia 0.2793 to 0.2798
Exhaust valve stem 0.2788 to 0.2793
Running clearance 0.0015 to 0.0025

[jakejakejake1]

Thanks a lot just what I was after,
Although it is for a 998, but as far as I know the valve stem diameters were the same and therefore the tolerances should be the same.

Cheers,
Jake

[carbon]

Old factory BL manual for Mk1&2 850's & Mk2 998 motor gives following dimensions in inches :
Inlet valve stem dia 0.2793 to 0.2798
Exhaust valve stem 0.2788 to 0.2793

Running clearance inlet valve stem = 0.0015 to 0.0025
Running clearance exhaust valve stem = 0.002 to 0.003

So an extra half thou clearance on the exhaust valve. Don't know if this still applies to later small-bore engines