MerCruiser 454 Valve cover noise, rocker arm?

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SeaingDouble

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My 1989 MerCruiser 454 has something banging the valve cover above the number one cylinder. It's a distinctive tap on the valve cover I can feel it. The engine is misfiring. Guessing I have a broken rocker arms or bent pushrod? Or do I have bigger problems? And please tell me I do not have to remove the exhaust Manifold to get the valve covers off. Mine have the little studs with the nuts Threaded on to them
 
Been there; done that. You can't tell what's wrong until you pull the valve cover. You might be able to sneak the cover out without removing the exhaust manifold. It depends on the exact exhaust setup. I had to repair bent valves a few times on our engines and was able to pull the covers without removing the manifolds. Unfortunately, I had had bent valves due to water intrusion and had to pull the heads, a real PITA. Labor to have someone else do it ran over $1k. Hope your problem is simpler. Don't let it go before it gets worse. Hy
 
Stock MerCruiser 454/340 with center rise manifolds. I’ve done a little bit of research apparently it is possible to get the valve cover off with a few special tools. Like a flexible extension and a swivel. We shall see. How will I know if I have a bent valves? Because I am 99% sure I’m going to find a broken rocker arm because I can feel it tapping on the valve cover. Or the rocker arm may have broken and the pushrod is going up and hitting the valve cover. One good thing in my situation, is there is no coolant mixing with my oil at all. That’s a good sign
 
Mush easier to remove the 2 end bolts, install longer bolts , remove inner bolts and just slide back enough to remove valve cover bolts
 
Yes that is a good plan, those exhaust manifolds are heavy!
About the noise, it is possible a rocker stud pulled out of the head and is allowing the rocker arm to just contact the valve cover, this would also reduce valve lift so the valve on that cyl is not opening all the way....
You won't know till you remove the valve cover....
 
hopefully the valve bolt loosened and not stripped. If stripped you may be able to use a thread insert.
http://www.acmeindustrial.com/insert_comparison.html

BUT YA GOTTA PULL THE COVER

Like alien said adding longer studs allows you easier manifold replacement and for this application, you can back off the manifold for easier manifold removal.
 
Thanks for the recommendations. A friend of mine just went through this on his boat with the same set up and he manage to get the valve cover off without removing the exhaust. Which would also be necessary to adjust valves. Anyway he let me borrow the exact tool combination he used which consist of a swivel socket and Long a quarter inch drive extension. Going to be attempting this today I’ll know soon enough. If for some reason that doesn’t work I will go do what has been suggested with the exhaust manifold. Hoping to find a broken rocker arm and nothing else!
 
Brett:

Really isn't that hard. Only the two bolts behind the center rise will be impacted. The other 5 should come right out and then it is a matter of wiggling the cover off. You may have to remove hoses if you have a closed cooling system. Before you do anything, set the timing at TDC with #1 on the compression stroke as it will make adjusting the valve a lot easier.

If you have a Mark IV (I think GM changed to Gen V after 1990)your valve train set up consist of a stud, pushrod guide plate, rocker arm, pivot ball and nut. The nut should have nylon threads. It is conceivable that the nut loosened or that the stud loosened but then the pushrod would be loose. It is also possible that the pushrod guide plate broke (happened to me). All parts are readily available and you will need a new valve cover gasket and a torque wrench to reassemble. Shouldn't take you more than 2 hours from start to finish. Don't forget to put assembly lube on the pivot ball and pushrod to rocker arm contact point.

Gene
 
Just tried my friends contraption that worked on his 450 for a MerCruiser. Not even close, not sure how the hell he got it to work. Looks like I’ll be pulling the manifold. It’s really unbelievable to me to have to do this to remove a valve cover.
 
UPDATE I was able to get the valve cover off just had to remove riser. Anyway what I found was the number five exhaust rocker arm had simply come off of the pushrod. Pushrod does not appear to be bent and the rocker arm itself not damaged or broken. The lock nut on the rocker arm doesn’t appear to have loosened just by comparing to the others. So, how can This have happened? Can I simply re-install this rocker arm and adjusted the valve and that is it? Or am I missing something?
 
Worst case, you have lifter that is not working properly and that requires pulling the intake manifold. But before you jump to that, pull out the pushrod and make sure it is straight. Roll it on a flat surface and check that there is a "ball" on each end. Possibly the rocker arm stud loosened? Specs call for torgue of 50#s with thread lock. Reinstall all with assembly lube. Rotate the crank until you get #5 on the compression stroke and adjust the value. Half a turn on the nut could be the issue.

If your down for the winter, I'd pull the intake manifold and take a look. All it costs you is a set of gaskets and time.
 
Well what I’ve decided to do, is adjust all the valves on both sides. If it’s still missing and spitting and sputtering I’m going to pull the intake and check the intake gasket and inspect lifters. I’ve already checked the pushrod it is not bent. I reinstalled the rocker arm with no issues. Unfortunately I didn’t notice A hint of moisture in the oil. Not detectable on the dipstick but I can see it on my socket when I am adjusting the rockers. Already did the risers that’s why I’m thinking possibly intake gasket. I’m not thinking head gasket at this point. I don’t see any signs of any freeze coming out of the exhaust
 
We used to find that problem with GM engines on cars in our shop. In all likelihood the valve rocker stud has pulled out of the block. Check the height of the stud compared to another one. The solution is to pull the stud and either replace it with a new pressed in stud or to tap the hole and use a thread-in stud. Any good marine or auto mechanic can do it.There are even kits available for you to do it yourself. The cause is usually a stuck valve or over-tightened rocker. Since it happened suddenly, it's probably the result of a stuck valve. Try tapping the valve with a hammer to see if it moves. If not, it may be bent or stuck from some rust, particularly if it's one of the valves near the center of the head. That would require pulling the intake manifold and the head to repair. Hy
 
If it's a collapsed lifter, you may be able to get it out with a magnet. The only problem is the magnet sticking to every surface. Otherwise, you'll have to remove the intake manifold.

you also might be able to check of collapsed lifter by pushing down on the push rod. The lifter is spring loaded as well as hydraulically. The oil should drain down so you can feel the spring. Mark the height. Turn the engine over til the lifter fills with oil and measure again. Might have to do this procedure a couple of times in case the lifter is on a cam lobe when you measure. It's a PITA but easier than pulling the intake. Oh, and get a one piece intake gasket. They used to be about $55 but well worth it as they're reusable.
 
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