Valve Oil Supply

The undated (but I beleive 1937) Instruction Manual that I have states "These rocker bearings are lubricated by oil mist from the crankcase but this should be supplemented by grease every 1000 miles. It will be noticed that two grease gun nipples are provided on the side of each rocker bearing boss on the rocker box fixed immediately above the cylinder head"

A friend is rebuilding a similar age Model 19 engine and we have also discussed rocker box oiling. One idea we came up with is to add a breather to the rocker box, maybe in the tappet access cover like the Kingpin breather for the later engines. If linked to a fuel line non-return valve (so that it breathes out but not in) that might encourage a flow of oil mist to the rocker box. Just a thought at this stage but not difficult to implement. On the OHC singles, which also have those small bore feed tubes to the guides, it is necessary to check the pipes periodically for blockages. Especially on the exhaust side where the heat causes the oil to carbonise in the tube.

Ian McD

The OHC singles of course have oil positively fed to the top end.  I don't know if there is a pressure feed to the tubes,  but I think it just runs out there by overflowing from the bevel box. (maybe?).

Other Norton engines of the period have drain tubes a bit like that in other places.  e.g. to the cavity around the tops of the valve guides under the tappets on the prewar 16H, where drain pipes descend to the ground, and to the mag drive (I think), so probably that's what they hoped for in the Model 18.  But if the rockers are occasionally greased, the excess grease is bound to block drain tubes.  Wasn't the issue recognised and rectified after the War?  The prewar (and WD) 16H makes do with grease nipples on the sides of the valve guides.

I did wonder John, but you referred to "valve gear in a real mess" and I took that to mean rockers as well...I've had serious problems with '36 pattern 16H valve guide wear...caused I think by fretting on the valve stems.

Modern plasma-coated valves from G&S seem to have helped but I'm suspicious of the solvents in modern fuels and their effect on borderline lubrication.

I'm also not sure about types of grease used in the 1930s...There were references in the manual to 'light grease' but the War Department listed a Compounded Gear Oil which was closest to an EP 140..hardly grease at all...I now pump engine oil into the guides with a Wesco before each run...It may not help much, but it can't hurt...There seem to be serious doubts about the behaviour of the solids in modern grease products when faced by cylinder head temperatures. They certainly haven't been tested for it !

Sounds like timing...maybe the mag sprocket slipped? Backfire can do that.