Stuck valve - cause ???
 

Went to start my port engine (525 EFI) last night and I could tell it was misfiring and shaking the boat. Shut it down right away and had my mechanic look at it first thing this morning. We took the rocker covers off this morning and we found a stuck valve. My engines have only 130 hours on them, have been serviced regularly and I mainly run the boat between 3000-3800 RPM (50-60mph). Sorry if this is a noob question, but what causes this?

You would be better served with this in general q&a. A lot more exposure and not boat specific. I am not sure of the answer but will be watching for te more experienced guys to chime in.

On that engine I would pull those headers and have him look for sings of water intrusion, like water deposits on the exhaust ports or valves. Those headers are known to leak, and a small leak can steam clean the oil off your valve stem, resulting in a stuck valve on the next start up.

There are of course 20 other things that could cause it. Be happy it happened at idle. Get those heads off, rebuilt and inspected. Pressure test exhaust.

Sounds like moisture for sure stuck it. Have him pop the top of that valve with a brass punch and see if it frees it up.


John jr

With all due respect, that may free it up, and it may be ok. But there is no way I would run that engine again without having the top end done. If that valve or any others stick at high rpm he could be looking at a total loss, vs 1500 bucks now

Oh I agree. But if it was random, not from sitting for a long stent it could be a issue or may not ever happen again. Also prob bent a push rod. Hopefully his mech is a good friend, if the head does have to come off, the mech doesn't break it off in this guys ass LOL. I just had to do this, it cost me about 50 bucks in gaskets( 1 push rod) honed the valve guide, polished the stem and about 6 hours of my time. Hopefully it doesn't cost 1500 but that is what people get to do it, it is a easy job.

John

4BUS, I think you hit the nail on the head (pun intended). The engine ran completely fine on Sunday and then when I went to start it last night, this is what happened. My mechanic said the exact same thing you did and he is pulling the heads and rebuilding. He also said I was lucky about it happening at idle as opposed to blasting the valve through the block and blowing the whole engine. I think I'm also going to put in inconel valves while we're redoing the top end.

Are the headers on the 525's the factory merc headers ? Just curious, because they are notorious for leaking. I would be looking for a diff set if so. Hope you get back up and running soon, for not a whole lot of dead presidents :drink:

John jr

Thanks John. I assume they are the factory headers because the previous owner didn't replace them, but I recall reading somewhere that there were two designs, and from what I've been told, I have the later/better design. I'm having the headers on both engines pressure tested. If all goes well, I should be back in the water by next weekend.

When I saw "stuck valve" and 525 EFI in the same sentence, that is the first thing that came to mind ... leaking headers. I know of a couple of new long blocks that were the result of leaking headers. The new design header is not that much better. The specific one's that I know had stuck valve => leaking header had the new style headers. One person actually had the engine back together when someone recommended he get the headers checked ... good thing he did that or he would have most likely trashed a brand new Merc warrantied long block! This was back in 2006 when all of this header awareness was beginning to really gain steam (pun intended).