Valve stem caps

Started by phutton, August 27, 2021, 05:42:58 PM

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Rick Parkington

Just a couple of points to add here, my '32 9A had valve stem caps when I got it and still has but they are probably unnecessary nowadays if you accommodate the space they take up with a slightly over-length valve stem. I suspect the reason they were fitted originally is that the valve material was not up to the hammering from the tappet adjuster - valve breakage was common in the early days of ohv so makers were probably cautious about embrittling stems by hardening, so a hard cap on a soft stem made an easy solution. When I got my 9A the valves were - bizarrely - modified Indian Chief valves with the heads reduced and the stems shortened. As I worked restoring Indians at the time I followed suit and modified a pair of modern repro Indian valves. I'm sure I could have made the stems slightly longer and dispensed with the caps but I chose not to.
The important thing is to ensure the valve strike angle is right so that the tappet adjuster is vertical to the valve at mid lift. If you fit a Sunbeam valve without a cap it probably will not be, so it's that that determines whether or not you need a cap. Also make sure the cap isn't deep enough to bear on the collets rather than the top of the stem or something bad is likely to happen...!
Cheers Rick


1946 BSA C11
1937 Sunbeam Model 9
... and a scratched Hyundai
(MSCR member)

Hot Tuna


The state of the Valves on my 9A when I got it in 1970 made me wonder about that.
Looking at the adjuster for the inlet valve on my 1932 engine I wonder if it is really feasible to fit on. With the valve closed there is only 1/8" (0.125") between the top of the adjuster and the frame.


The 1929/30 parts list includes the hardened cap that goes on the end of the valve stem for OHV models (p/n 5031). It is not mentioned in any other parts list until 1938. Can anyone tell me whether OHV models in other years did actually fit this cap? Did JML just leave it out of the parts lists, but still fit it? All OHV M9 valves are the same from 1927 until 1936, so it is a bit of a mystery.