What will I find?

[TilliamWe]

Ok, everyone, time for me to admit to another dumb thing... <br />I have a 1997 Mercuiser 5.7 EFI Gen + (280hp throttle body injected) with a Bravo 3 drive, with 650 hours on it. I'll spare all the details,(but it's still long story, sorry) but it has much unburned gas in the exhaust, and it's very noticeable at idle. Funny thing is, it runs at cruising speed (3000rpm) perfectly all day long, and has for quite some time. It'll even turn 4400-4500 at WOT (it use to turn 4900). So, I've done a compression check and one cylinder on the left (5) was lower than the rest, but not bad. However #2 had ZERO compression. So the right side valve cover came off. Good valve train action. Adjusted valves on that cylinder, and lo & behold, backing INTAKE valve WAY off, I got 90psi. But when adjusted it to stop the noise, it went to zero. Measured valve stem height, and oops, that valve is much higher than the rest. We turned the valve & got 60psi. Put it back together. Now the motor won't go over 3700rpm, but doesn't smoke as much at idle. <br />So, the heads are obviously going to be pulled. What am I gonna find? Just a tulipped valve? A bad seat, a junk head? Is this common? On an intake valve? Any thoughts or insight will be appreciated. Thanks

 

[TilliamWe]

Re: What will I find?

Aww, come on Rodbolt, Bondo, and Don S... i gave you the perfect opportunity to scold me & make fun of me, and you just let it go? Especially you Don, after you wanted to tease me about my B3 drive installation snafu this spring!<br />So, what do you think? How bad will it be? Is this common?

 

[Don S]

Re: What will I find?

I don't know what you are going to find, I can't see inside your engine any better than you can. <br />Since you have to pull the head, best thing to do is look. If you want, you could do a leakdown test.

 

[olbuddyjack]

Re: What will I find?

Probubly just a valve or two but its gonna need a complete valve job anyway. Drop em off at the local machine shop and let them redo them. <br />Thing I'd be concerned with is why it happened. Usally its caused by high cylinder temps from lugging but your wot rpms look good. Maybe running lean?<br />Don't forget to check the piston tops good around the edge for burning.

 

[TilliamWe]

Re: What will I find?

Jack, thanks for this nugget:

Usally its caused by high cylinder temps from lugging

Actually that has occurred... when the bottom gets very dirty, the boat has to work much hard to attain WOT. I will definatly keep the bottom cleaner.<br /><br />Don S, I knew you couldn't see inside the engine. Just wondered if you had a "guess" as to what would be there. Also wondered if you knew if these heads did this a lot, and if they will survive this "abuse". But thanks for the info.

 

[deputydawg]

Re: What will I find?

Could be anything from carbon on a valve to a burned valve, cracked seat, tuliped valve, bent valve stem, and the list goes on. <br />Don't forget to check the top of the piston good for any marks. Kind of sounds like a bent valve. Could have had a speck of carbon or rust corrosion on a stem causing it to stick slightly open, the piston tapped it and bent it slightly.