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).

Oh yes. After a day of researching this, I'm convinced that I have fallen victim to the 525 header problem. I am going to replace the headers on both engines now... Any opinions on what I should use? I'm thinking either Stellings or Hardin Marine Typhoon 525 headers... thoughts anyone??

Is it a staggered boat? Happen to be the starboard side? Captains call? My buddy has an 08 525 boat and for the 3rd (yes third) time in 300 hours it reverted bad enough to rust the valve stems on the rear two exhaust valves. This boat has new headers on it (within 10 hours) and did it this time recently again. Mercury put a motor in under warranty when the boat was new and said the cause of the failure was a combination of a rigging issue from Fountain and the fact that the silent choice mixed water too close to the collector. This time around the silent choice came off... so fingers crossed. Reason I posted is that the failure happened exactly the way you stated. We ran the boat one week flawlessly, next week we started it for a poker run and it was missing and carrying on the second it rolled over.

Yes, it is a semi-staggered boat, but its the port engine and I do have silent choice. When you say your friends boat had the same issue again with new headers, was it the CMI mercury spec header or did he replace with something else? I'm going to change the headers; I'd hate to think thats not going to solve this problem..

First I would have them tested just to make sure that was the cause..

Check the tails also. Tails have been known to burn through near their highest point where water can't maintain level.