by Bob Donalds
| There is no substitute for experience
so I thought that I would share a few of those experiences which can
bring you up short. In other words,some lessons are well learned. I
have made most of the mistakes one can make under the valve cover and
I have reviewed the remains of other people's mistakes for instance,
rubber mounted rockers when the wrong rocker gaskets are used by mistake.
Do you have any oil leaks?
What is so complex about the stuff under valve cover? Looking at it you see a metal cover, the clips (bails) that hold it on, some bolts the gasket the rocker arms and the often fooled-with adjusters.
I have made some expensive mistakes with the valve covers that I have installed. One such example comes from my racing days. One day at the track just before the race,and after adjusting the valves I reinstalled the valve covers on a Formula Vee engine. I had done that many times before. No big deal, right. I found out the hard way that the valve cover was leaking it. The car was smoking to beat the band in the hard right turns. I had not checked the covers for leaks. I lost the race, the crankshaft, and the connecting rods. However I gained experience which has lasted 20 plus years; check your valve cover for leaks every time you reinstall them. That means let it run and look to see that it is dry. It may take a few minutes for the oil to get up to the cylinder head. This effort is well worth the wait. When installing the valve cover always I put a fresh gasket on! I do not glue them on so I can't get them off later. If it still leaks try a new bail . They are less that two dollars at the dealer and they hold the cover tight against the head. You may find that the valve cover is just too old, rusty or bent. Try a new one.
So your heater box is wet with oil and your'e sure the cover isn't leaking. Push rod tube gaskets and lower head studs can be responsible. There are expandable push rod tubes to repair any leaks that come from the tubes or tube seals. When rebuilding air cooled engines I seal the studs inside the valve cover with silicone (non- corrosive kind). This could also be done at any time if the parts are free of oil. By the way, on some of the early 36 hp and 25 hp engines the lower cylinder head nuts had an o-ring which seals the lower stud holes.
Adjusting those valves must the simple part right? So you just adjusted your valves but they sound like the Hammers of Hell'. What gives? The answer may be the head temperature. The valve lash increases with temperature on all but the oldest stale air engines with long rocker studs. Anytime the oil temp goes over 200F degrees the cylinder heads can over-heat and that can show up as a noisy valve train.
Perhaps the engine is not too hot but one or two valves are ticking away. You've gone back and tried adjusting them again and you are sure that the valves are set correct but the ticking noises remain! What to do? One possible answer is that the valve is not adjusted to the clearance of the feeler gauge you've used. The gauge simply bridged the dish in the end of the valve stem.
Since the tip of the valve stem wears over time, it's possible the feeler gauge can not flex enough to accurately reflect the lash the rocker will have and thus the ticking noise. Try adjusting it by feel with no feeler gauge. The rocker needs to move about the thickness of a dollar bill (.004ths).
Lash caps are one way to deal with valve stem wear These go over the stem and give you a flat surface. The rocker stands may need to be shimmed to make room for adjustments. I shim the rockers on every engine I build to set the geometry. Every manual covers geometry but its rarely paid atten valve guide.
Also repeated loss of valve clearance on the exhaust valve indicates stretching valve stems or valve seat erosion. It is then time to remove the heads for inspection and a proper valve job.
I hope sharing my experiece's under the valve cover helps you avoid some of the problems I've incountered. As a famous guy once said "Those who don't know history are doomed to repeat it".