1987 3.7 Mercruiser odd behavior

[MTBoat]

When I went to fire up my 3.7 four cylander for the spring, it was difficult, and when it ran, I could pull the front spark plug (I assume #1 cylander) and it would run nier and speed up. ( I put in a new plug as well).

Anytime I take the wire off the front plug, the whole engine runs more smooth on 3 cylanders and speeds up. Hook up front plug, it runs slower and rougher.

I don't recall ever doing anything to cause this. Any idea what is going on?
Thanks

 

[wrench 3]

The only thing that comes to mind is an intake valve not closing properly and blowing exhaust back into the intake. Try a compression test.

 

[stonyloam]

So, the plug firing slows the engine RPM? that would indicate the timing on #1 is way off. If the wires are correct, maybe you are getting some spark jumping from one wire to another?? Either dirt or a crack in the cap or bad wires? Try cleaning the cap and checking that the wires are correct and well separated. Maybe a stuck exhaust valve would do it. Check the timing with a light. A compression check might be in order too.

 

[stonyloam]

So, the plug firing slows the engine RPM? that would indicate the timing on #1 is way off. If the wires are correct, maybe you are getting some spark jumping from one wire to another?? Either dirt or a crack in the cap or bad wires? Try cleaning the cap and checking that the wires are correct and well separated. Maybe a stuck exhaust valve would do it. Check the timing with a light. A compression check might be in order too.

 

[MTBoat]

I kind of think that's the situation, I had an overheat last year when kelp blocked the intake for cooling. I wonder if that caused this sticky valve.

Is there any fluids or solutions that can actually unstick this, and is it highly dangerous to run it at all with that intake valve not closing properly.

Obviously, I'd like to not have to pull the engine or head, or whatever the mechanical procedure would be.

 

[stonyloam]

Sorry about the double post. Yeah wrench could be right, one or the other LOL. The overheat could be the problem, if you blew the head gasket, could be coolant got in there over the winter and you got a little rust in there. In any case, the first thing is a compression check. Let us know the results. Head gasket is not a really bad job. If you do need to pull the head, a OEM Mercruiser head gasket is a must. If you need to have head work done, you might consider having hardened exhaust seats put in. Good luck.

 

[MTBoat]

I removed the valve cover and found the culprit. The$275, no idea how much to have the existing one fixed, and no idea how hard it is to pull the head and replace. Seems pretty cost effective if I can do the work myself, but, I imagine pretty spendy if I have it done.
Anyone ideas or experience pulling a head and replacing in terms of how difficult or what to look out for, or the cost to have this fixed my mechanic?
Thanks

 

[wrench 3]

If your at all mechanically inclined you should be able to remove and reinstall the head. To readjust things after assembly you might need to be fairly mechanically inclined. If the head needs to be resurfaced and that valve is bent, I'd still expect a repair to be cheaper than $275. You'd have to contact a local automotive machine shop.

 

[stonyloam]

What did you find? Bent pushrod? What is $275?

 

[MTBoat]

Sorry, the edit removed some of my explanation. I found one bent, cracked pushrod at the 2nd valve in from the back, not sure if intake or exhaust... And I saw used heads for around $275 or so, If I could do the work myself, not sure what all has to come off, and how much for gaskets for all? And I understand some have different sized push rods?

I was trying to decide whether to order a head, or just pull this head and take it to be fixed, and/or have it done. I am afraid that having it all done will be very pricey, and I can do most things mechanically basic, but, not sure about getting push rods right and setting valves on install etc.

So, advice on handling this one is appreciated. I am wondering if this alluminum block could be warped, or just the head from overheating last year, it was a bummer the intake got plugged and overheated before I realized it,no buzzer sounded.

 

[Bondo]

Sorry, the edit removed some of my explanation. I found one bent, cracked pushrod at the 2nd valve in from the back, not sure if intake or exhaust... And I saw used heads for around $275 or so, If I could do the work myself, not sure what all has to come off, and how much for gaskets for all? And I understand some have different sized push rods?

I was trying to decide whether to order a head, or just pull this head and take it to be fixed, and/or have it done. I am afraid that having it all done will be very pricey, and I can do most things mechanically basic, but, not sure about getting push rods right and setting valves on install etc.

So, advice on handling this one is appreciated. I am wondering if this alluminum block could be warped, or just the head from overheating last year, it was a bummer the intake got plugged and overheated before I realized it,no buzzer sounded.

Ayuh,.... At this point, ya don't know whether yer head is still good, or not,....

A Machine Shop can tell ya,....
A bad valve ain't a bad head,....

 

[stonyloam]

Second from the back would be #4 not #1, common for blown head gasket in a 470. The biggest pain is draining the antifreeze. There is a drain in the block, but I THINK you could do it with a section of hose and a funnel. Run the hose out the drain hole for the hull, put the funnel in the other end and hold it under the forward plug on the exchanger. Pull the plug and the coolant can drain through the hose into a bucket. That should get most of the coolant out. As for removing the head, the book says to remove the intake and exhaust manifolds before pulling the head. After doing it myself, I think you could just remove the carb and controls, disconnect the hoses and exhaust pipe bellows and pull it all at once. Disassemble it on the bench. It would be a two person job, because it is pretty clumsy and heavy. for your bent pushrod, straighten it out and take it to your local Ford dealer and get a matching Ford 460 pushrod. When you replace the head gasket it is important that you use a OEM Mercruiser head gasket, they are designed specifically for the 470. Hope this helps a little.

 

[MTBoat]

Great advice. Will endeavor to do this and have a good machine shop ready to see if they can fix me up....but the antifreeze drain does seem important or a big mess.