Sick Mercruiser V8

[6meter]

Re: Sick Mercruiser V8

I thought about that too, but I would have thought that by now it would have broken apart and blown out. I guess the only to know that one for sure is to pull the heads.

Sometimes they don't, they just stay in there and make a racket. GM used to make a product called Top Engine Cleaner. I used it years ago. You also could use water but you better know what you are doing. Bent rods also require engine removal.

 

[mnypitboat]

Re: Sick Mercruiser V8

OK update. I ran it tonight and while running it I greased up the gimbal bearing with no effect. I was hoping for a noise change or something but nothing.

I checked the compression, and all 8 cylinders read between 135 and 140.

Next step was to run some seafoam through the intake. It really started clattering then. So confirmed that its in the engine for sure. And likely in the valve train. So I ran the whole can through. Then I changed the oil and put a can in the crankcase. After about 15 minutes it got quieter. So I am gonna take it on the water tomorrow and see how it goes. I am hoping I collapsed a lifter or something. If not I guess the heads will be coming off.

The good news is that I found a complete 350 with a forged and blueprinted bottom end with 10.5 to 1 pistons and a nice cam, aluminum intake, MSD distributor, Holley 4bbl. The only problem is that its from an early 90s GM truck.

So I guess my question is, how much differance is there from a marine to an auto application? Can I use this engine? It is almost free, so if it blows up, its just labor. If I take it easy, I would think it would last a long time, or at least til I can get my old one rebuilt. How hard is it to convert the carb to work because currently I have a 2bbl.

 

[jtmarten]

Re: Sick Mercruiser V8

The MSD and Holley would have to go unless they're USCG certified. Depending on where the cam makes power, it may scream, it may be a dog and not even get on plane. For long-term use, swap the freeze plugs for brass plugs, especially if you run in salt or brackish water. If the clearances on the mains were setup for automotive use, I wouldn't run her full throttle for 30min, you'd be spinnin' bearings or slingin' rods everywhere.

 

[Bondo]

Re: Sick Mercruiser V8

Ayuh,... 10.5:1 is about a point Too High,+ a lopey cam is a Bad thing in a boat....

Maybe thicker headgaskets,+ a different cam...

 

[mnypitboat]

Re: Sick Mercruiser V8

Its not a big lopey cam. It was actually built for towing. Very low horsepower for a "built" engine, but pretty high on the torque. If you heard it run, it sounds stock. It was built by a pretty reputable engine builder.

I was thinking I would get rid of the MSD anyway. I can use my old distributor. What is the big differance in carbs though? I can still put a flame arrestor on it cant I? I am not looking for a screamer, just an engine to get me by for a while. I figured with what he has done to the bottom end would make it a decent candidate, especially for the price.

 

[littlebookworm]

Re: Sick Mercruiser V8

The carb and fuel pump must be marine specific. For a start, there's an extra thin hose between them which directs gas into the carb in case of a diaphram break. You don't want fuel leaking down into the bilge. The freeze-out plugs need to be brass. The head gaskets need to be brass or composit; steel headgaskets will rot out quickly. The distributor also needs to be marine. The one from your present engine may or may not work.I can't say for sure because of a number of variables. The cam really should be toned down or you're liable to suck in water when you decelerate. If you do install the engine, don't over-run it; you'll blow your drive. It might be easier and cheaper to just pull the heads and check them out. Rebuilding the heads is no big deal; any auto engine shop can do it. Good luck. Hy

 

[mnypitboat]

Re: Sick Mercruiser V8

The carb and fuel pump must be marine specific. For a start, there's an extra thin hose between them which directs gas into the carb in case of a diaphram break. You don't want fuel leaking down into the bilge. The freeze-out plugs need to be brass. The head gaskets need to be brass or composit; steel headgaskets will rot out quickly. The distributor also needs to be marine. The one from your present engine may or may not work.I can't say for sure because of a number of variables. The cam really should be toned down or you're liable to suck in water when you decelerate. If you do install the engine, don't over-run it; you'll blow your drive. It might be easier and cheaper to just pull the heads and check them out. Rebuilding the heads is no big deal; any auto engine shop can do it. Good luck. Hy

I am planning on running it tomorrow on the river and see if its still as loud after I put the seafoam stuff in there. If it is getting quieter, then I am guessing a lifter. If not, I will be pulling the heads or having someone pull them(depending on time). I am just concerned that if I damaged a lifter that it also damaged the sleeves where they go in the block. I have had this happen on cars in the past and needed a block. If this is the case then I will be looking into this option more seriously. I will do the brass plugs and head gaskets. Probably just bolt all my old stuff onto the longblock. My understanding is that Mercruiser engines are based on the truck block anyway, so I am thinking it should all fit. I can get a marine cam pretty cheap, or if mine is ok, just swap it over.

This all depends what we find when we get the heads off. It might be something simple like a bad lifter or a bent valve.

 

[jtmarten]

Re: Sick Mercruiser V8

Marine Holleys have 'J' overflow tubes, and marine base plates with different bushings/seals to prevent leaks through the throttle shafts.

 

[Big Boat Bay Buster]

Re: Sick Mercruiser V8

I think you are jumping the gun a bit about getting another engine. How about the frequency of the noise. The valve train will turn at half the speed of the crank. Its not too much work to pull the intake manifold and inpect the cam shaft and valve train more closely.Check out Summit Raceing for a set of Lifters, rockers and pushrods--raceing quality--Real cheap. Be careful, another run on the lake may be all thats needed to do more damage!
Chris

 

[mnypitboat]

Re: Sick Mercruiser V8

I am just getting ready for the worst case. I am pulling the intake today, then maybe the heads. Took it to the mechanic and he said these engines are known for piston skirt colapse, and the more I think about it, a piston slap could sound a lot like a valvetrain noise. The more I think about it the more I am thinking piston slap. We will see after the intake comes off, then the heads. Then block.

 

[mnypitboat]

Re: Sick Mercruiser V8

I am just getting ready for the worst case. I am pulling the intake today, then maybe the heads. Took it to the mechanic and he said these engines are known for piston skirt colapse, and the more I think about it, a piston slap could sound a lot like a valvetrain noise. The more I think about it the more I am thinking piston slap. We will see after the intake comes off, then the heads. Then block.

Intake off, inside looks like a brand new engine. I am nutz about maintanance so it doesn't surprise me. So this morning I pulled the port side head, and again, looks like a new engine. Still has crosshatch marks in the cylinders. This is driving me crazy. I had to take a break, so I will pull the other head this afternoon.

I cant get over this. What the hell could it be???? I guess it must be in the bottom end somehow, maybe a wrist pin resonating up into the heads?????? Why cant it be something simple like a broken piston or something?????

OK well at least I know what engine I have now. It is definately a 5.7, and it has 906 heads on it. From what I have read they are Vortec heads used in heavy duty GM applications. Poor flow, but solid. Not that it matters at this point.

 

[carcraze]

Re: Sick Mercruiser V8

Keep us posted when I first saw your post my thoughts were spun rod bearing or piston slap as I read through. My experiance in the past though is piston collapse after an overheat or rod bearing spin after high RPM split second oil pressure drop. I am interested to see what you find.

 

[mnypitboat]

Re: Sick Mercruiser V8

Keep us posted when I first saw your post my thoughts were spun rod bearing or piston slap as I read through. My experiance in the past though is piston collapse after an overheat or rod bearing spin after high RPM split second oil pressure drop. I am interested to see what you find.

I would think piston slap would have made some kinda marks on the cylinder walls?? A spun bearing would not have made it nearly 50 hours. Wrist pin, well maybe.

I am completely lost on this one. I completely expected to find something either broke or bent. Especially as loud as it has gotten. I am not even speculating at this point. I am just gonna keep tearing it down til I find it.

 

[carcraze]

Re: Sick Mercruiser V8

I had a Camaro spin a rod bearing once at just over 6500 rpm. Sounded terrible, and sounded like it was in the top end. Engine ran fine, other than the loud knock, finally once I pulled the heads you could see where the piston top was tagging the combustion chamber, other than that it ran okay.

 

[mnypitboat]

Re: Sick Mercruiser V8

Well, I found it. It appears that the headgasket was oblonged above cylinder 4 and 6. It appears to have been leaking water into both of those cylinders. the bores are a little beat up and the top of #6 has what looks like corrosion all over it too. So it appears that piston slap was the issue. I swore it was coming from that side all along, but everyone else that listened to it said it was from the other side. The head gasket looks to have been torqued down messed up, so this has probably been oblonged since new, and finally took a crap.

I still cant understand how my compression check came back all within 135 to 145. It doesnt make sense.

Either way. What do you guys suggest I do now?

 

[mnypitboat]

Re: Sick Mercruiser V8

I SCORED!! I had a WTB ad on Craigslist and a guy called me last night. He claims to have a complete(I mean complete from oil pan to carb to manifolds etc etc) Mercruiser 350 from a boat that was written off after a forklift went through the hull. It supposedly had 18 hours when pulled. All this for $500. I am still a little skeptical, but I am going to look at it around noon. If it is what he says it is, I will be coming home with it. Then to get it installed.

I have a long weekend next weekend, Sat-Tues, but I am still working on lining up a shop to use and a person with a little more knowlege about boat engine swaps to help. Hopefully I will be back on the water in a week or so.

 

[mnypitboat]

Re: Sick Mercruiser V8

Well ok, got screwed. The "new" engine with 18 hours turned out to be an 88 with no compression. We decided to do a compression check before installing it and we got 120 on 2, 20 on 4, 180 on 6, 120 on 8, and we stopped there. No point going any further, I got screwed and that is about all.

Now I am gonna rebuild my old one. I should have done that to begin with. I was trying to save some time, between not wanting the boat down too long, to the shop we were using, and the help, I wanted to pull the old engine and replace it the same day. Turns out, the shop fell through, the engine was junk, and the guy helping can come back. What a waste.

Moral of the story, compression test engines before you pay for them.

 

[mnypitboat]

Re: Sick Mercruiser V8

Finally found the source of my rattle. After tearing the engine apart, I still didnt see anything. Started cleaning up the heads today and found one of the valves, on cylinder 4, pushed in, so to speak. Its pushed in and cracked. I didnt see it til I took a wire brush to the chamber. So it appears that I will be replacing at least that one valve. Against my better judgement, but due to money constraints, I was gonna bolt them back up. Glad I found the valve issue before I did.

 

[mnypitboat]

Re: Sick Mercruiser V8

Oh and I pulled the heads off the other engine, and it appears that it has exactly the same problem on the same cylinder. What a coincidence. Strange.

 

[Bondo]

Re: Sick Mercruiser V8

Ayuh,... Sounds like they went Lean,+ detonated to death...