Sandahl

I have two normally aspirated, carb'd 540 tall decks with Merlin 345cc heads and solid lifter cams. One of the engines is going on two years with zero problems.

The other engine is solid except that one exhaust valve on one head keeps sticking. It is in the #4 / #5 position (depending on which side you put it on). It happens after the boat has been run and then parked for a week or so. I even fogged the engines down after running.

Last time around I switched the heads from side-to-side and the problem still recurred in that same cylinder of that same head. This eliminates my original suspicion that I had a water leak in the exhaust specific to one side. During 3-4 attempts in the past year, the valve (inconel) has been replaced at least once, as have the guides (bronze) at least once. The last time around I had the guide clearance increased. I have new valve springs all around now and the roller rockers and pushrods have been switched around various times, but it is always that same cylinder. The other 15 of my total of 16 cylinders have never given me a problem.

Since nothing makes sense about this, I am about ready to just buy another head! Any other ideas?

GO4BROKE

Is the valve seat perhaps wrong? Binds the valve after sitting for a while? Really reaching here but I can't think of anything else. The seat is about the only thing unchanged in all the work you have done.

Sandahl

It's sticking open, so could the seat be misaligned and bend the stem after some time?

Last time around, it would idle ok for about 10 seconds then die when the valve stuck open. Then in the silence about 5-10 seconds later you could hear the valve "plink" back into place if the cam end up where that was allowed.

Dennis Moore

It would seem that the valve guide/valve stem is not getting enough lubrication. Install loose fitting valve guide seals on the exhaust valve guides to increase lubrication. Check to see that the lifter is pumping the same amount of oil to that pushrod/rocker arm/valve stem as the other lifters.
Dennis Moore

JimV

If your using teflon seals, try removing the metal ring on top of the seal. Check the valve stem for excessive heat. Does the oil on the stem smell burnt? Is the stem darker or discolored higher up the valve? Check the exhaust gasket for a header leak. How does the plug look? How's the valve train geometry?

Ted G

There may be a cooling problem at that part of the head that is not allowing proper heat dissipation from the valve and/or guide. If the valve and guide both swell due to excess heat it will bind the valve. When you shut down it cools quickly and plink goes the valve.

Elite Marine

I have the same problem. We verified the clearance and checked alignment..all good. We couldn't Identify the brand of valve though, so i switched to Rev Valves on the exhasut. Engine should be in the boat this weekend.

I had the same problem on the dyno. We opened the guides a little. Seemes to work for a while until I tried getting over 5000 RPM. Hence the rebuild of the heads.

I would recommend opening the guides and removing the steel retainer on the seal. Dennis Moore recommends stock valve seals on exhaust valves. So what if you get a little smoke at start up if all runs well while underway!!

Good luck!

Budman

You did not mention if the rocker arm stud and/or pushrod guideplates have been replaced. Any misalighnment or bending in this area could put things in a bind.

Also, someone mentioned heat dissipation. Could there be a problem with the valve seat, i.e., seat too narrow or seat not making good contact with cylinder head material. If the heat can't transfer to the cast iron of the head, valve will swell and bind in the guide.

Oh yeah - if you decide to get another head, someone was looking for a single Merlin head on this board earlier. Can't remember if they had oval or square, though.

GO4BROKE

Any thing bent wouldn't let the valve close a few seconds later. I think the safe bet is to follow Dennis Moore's advice. You also might want to check the lifter and bore for scoring.