Valve stem seals

Previously wrote:

I doubt that it matters what type of seal is fitted. Even an old seal carries on doing its job, and a small amount of oil weeping down the valve stem is a good thing. Are you sure it has not simply jumped off? One of mine did that immediately after I had serviced the head (my fault failing to ensure it was not fully seated?) and I had a lovely oily plug and exhaust pipe outlet for one thousand miles until I rectified it.

Hi Norman

That's exactly whats happened, I made up the tools to do the job today and after I had lifted out the springs the seal just lifted off the guide.

I've replaced it as a matter of course and made sure it got a good push down with a suitable sized socket, if it's nice tomorrow I might get out on it and see about getting some more miles under it's wheels.

Previously wrote:

Because nobody has come up with a reply so far, maybe my vague response may be the best you will get!

In the dim and distant past I seem to remember fitting some valve stem oil seals with springs around the top. To get them I went to our local, good engine reconditioners who searched through their oddment box and came up with some, they MIGHT have been from a Ford.

Hope that this is at least of some help.

Hi Richard

I've just used the standard VITON seal again as the problem was the seal lifting off the guide, we'll see if it happens again.

Out for a run today and the R/H looked great but the L/H started showing the same signs, and further investigation revealed the same problem, so it's now going back together with another new seal.

Previously wrote:

Early Commandos had no oil seal fitted and I presume the same could be said for all heavy twins. You should not have to rely on the oil seals to stop oil being drawn down the guide they are there merely to reduce the flow. You say you have rebuilt the cylinder head, did you fit new valves and guides? if so did you ensure there was no scoring to the bore in the head that the guides fit into. Damage in this interference fit will result in oil being drawn down the side of the guide. Oil getting past the valve guide will manifest itself on the overrun when there is an increased vacuum in the inlet port and this will suck oil down the guide. You may have excess oil in the cylinder head from an incorrectly fitted rocker spindle. The flat on the spindle should face away from the pushrod end of the rocker.

Give us some more information as to when it's smoking and what is new on the engine. If it's just smoking it could be the bores, if it's smoking after a period of running, the rocker chamber could have filled with oil.

Hi Dave

The symptoms have just manifested after a +20 rebore and Head service, valves and guides were fine but the seals had seen better days and were a bit hard. Engine has run fine and smoke free for 200 miles and has now just started, first on the R/H pot only so that was replaced in situ and then the day after it was changed the L/H decided it wanted to be changed too. In both cases the seal had popped off the guide so everything else in the head is in good order.

Previously wrote:

Hi Mac,

Sounds like there is some wear in the valves and guides as they shouldn't smoke even without seals fitted. Have your inlet valve guides got the groove to accept the oil seal? Early engines didn't have seals fitted and hence didn't have a groove to locate them.

Dave

Hi Dave

Valves and guides were brand new back in 1987 when it was last on the road and it's probably done a maximum of 400 miles since they were installed. The guides do have a groove for the seals to fit into I'll just have to see if this pair stay on and if not will have to look into why!