[oggers]

I have no idea if it is normal - it seemed to work though! No pic, but it really is just like a bolt head with a slight dome.

[Thomas]

Is that the normal setup? A picture would be great.

[oggers]

Interesting stuff. On mine (1931), the part of the tappet that locates onto the stem is a slightly domed hex head of around 1/2" AF. It looks to be smooth - no obvious indents. The portion of the hex head that has clearly been in contact with the stem is fairly central to the head and around the same diameter as the stem.

[Thomas]

The face of the adjuster should have a slight radius.

Yes, they should have a certain radius equal to the distance between the centre of the rocker arm shaft and the centre of the tappet. In my case this radius is about 45mm and the tappet has a diameter of about 10mm. With these numbers the resulting height for the tappet surface from edge to centre is only 0.3mm (calculated from the equations for a circular segment - https://en.wikipedia.org/wiki/Circular_segment). The picture of the exhaust tappet at my 1937 M9 shows how it should be. Its face seems to be flat at first sight but has a radius matching with the arm length. However, a previous owner heavily underestimated the radius at the inlet valve. The outer part has been once unnecessarily ground off.

So, you should measure your rocker arm length (maybe it is different to my engine) and then calculated the tappet radius accordingly (if necessary).

Cheers, Thomas

[singleminded]

Yes that's correct. It's worth checking the adjusters to see that the surface that opens the valve is smooth and that it is not dead flat. The face of the adjuster should have a slight radius. You may be able to see the difference between the left and right adjusters on my 1932 rocker  box, the one on the right was shot.

[oggers]

Many thanks for that - very useful to know. Bike is in bits being restored and the rocker plates are away being re-chromed. I'll certainly look out for it.

Another one if I may. The tappet adjuster locates directly onto the valve stem. No cup or anything similar. Is this correct?

[phutton]

If you look at the offside rocker plate, you will see a small screw (it is actually 3/16 BSW). It is usually to the right of the centre stud, but it can be to the left as the plate is symmetrical. Its purpose is to allow oil to be squirted in on assembly, or when the machine has been standing for some time.

[oggers]

Understood. So perhaps best to lube up the rocker box well before starting after an engine strip? I guess it explains the grease nipples.

[phutton]

There is no direct oil feed to the rocker box on any of the side-plate type boxes, including the 1931 models. Lubrication of the rockers is by oil mist forced up the push-rod tubes on the downstroke of the piston. This is why there is no breather on the OHV models, but there is on the SV models.
P.

[oggers]

Chaps

How does the oil get to the rocker box? I have seen a cutaway diagram in the manual and it seems to indicate oil is pumped up near the pushrod tube, circulates around the rocker box, before returning down the pushrod tubes to the sump. I am intrigued as to how it gets to the rocker box.