Problems with valve lifter - wrong rocker arm perhaps?

[volker.halbach]

I went to the Drags site: You need the steel push rods with 10 5/8" effective length, part no. 1856-39 for a cast iron engine. The old ones should be 10 3/8″ (always measuring from the tip of the lower end to the inside of the cup).

The 10 11/16" are for the later alloy head.

[stevewhitt]

So, This morning, I removed the rocker box, extracted and measured the push rod etc; convinced myself I needed a longer pushrod. This afternoon, I thought, lets just reassemble with what I have and educate myself along the way. It seems to have gone back together correctly now, allowing the exhaust lifter mech to work as expected, and with much more thread showing on the tappet adjuster. I saw this engine running (briefly) when I bought the bike. I am confused now as to how it can go back together so differently. Here is a picture before I took it apart and a picture with it reassembled this afternoon.
I can only conclude it wasn't assembled correctly when I bought it - pushrod not lining up with rocker arm perhaps?
Any ideas anyone?
Or, has the pushrod not gone in correctly this afternoon, creating a slightly longer pushrod? They do just drop in, don't they?

[will_curry]

I'm not sure it's appropriate in this case but leaving the rocker box
gasket out makes an appreciable difference.

[stevewhitt]

Ah, I did think of that Will, so I jammed parts of the old cork gasket around the base of the rocker box (new aluminium one arriving soon).

[volker.halbach]

That's mysterious. And it's quite a difference. Does the valve really open in the normal way when you turn over the engine?

[stevewhitt]

The engine does appear to turn over correctly. I have taken the inlet pushrod out, its 1/8" longer than the exhaust side! So, I took the head off to remove the pushrod tubes (needed to replace the sealing washers anyway). Peering down onto the cam I am surprised there is an offset in the position of the cups (see photo) - is this normal?
To summarise : Exhaust pushrod measures 10-3/8"
Inlet pushrod measures 10-4/8"

The pushrods look identical, other than length.

There are some vice jaw marks on the exhaust pushrod, as if someone has in the past tried to undo the ends.

Maybe 1/8" can be taken up by the tapper adjuster, so nothing to be overly concerned about?

[Simon.Gardiner]

Steve
The offset followers are correct for a two-lobe cam (these can come in two different base-circle sizes, although the smaller one would be relatively rare and was only used for a couple of years at the start of the 1950s).
So if you swap the push-rods around (longer one in the exhaust side) does that fix your problem with the lifter?

SG

[volker.halbach]

It's worth getting the length of the push rods right. The tappet adjuster and the valve stem should be in line with the valve half open. With the adjuster completely screwed in, the valve stem is always pushed to the outside, and valve guide and valve wear out more quickly.

Sometimes the standard push rods don't fit. The valve could sit too high (after the enthusiastic valve grinding of generations of previous owners), the cam followers could be heavily worn, etc. Originally there were caps on the valve stems, which also make a difference.

[dennis.t]

I had this problem with the push rods appearing to be too long. It turned out that the ball ends were a poor fit in the cam cup. The solution was to use grinding paste to get a better mating of the ball and cup and confirm the fit with engineer's blue. The push rod then sat lower in the cam cup and reduced the rod's effective length. The rocker then sat in the correct position for the valve lifter. The bad news is the grinding really needs to be done with the cam cup on the bench in a soft jaw vice.
Dennis