Newbie with Sportjet 120, strange compression numbers and

[gcglastron]

Hello,
I am a newbie to this board, but from browsing, it seems to have some very knowledgeable people who I hope can help me. I have a 1995 Mercury Sport Jet 120 HP which was running well past several years. However, a couple weeks ago, I took her out for the first time this summer, and had problems starting the motor (I did winterize it). After wearing down 1 battery, I brought her home, replaced the plugs, checked spark (all good), and took her back to the lake where she started up. I let her idle about 15 minutes, but then the overheat alarm came on - first time it has come on other than when I tested it during maintenance. I felt the engine, and the top of the exhaust manifold was untouchably hot, whereas the lower part of the exhaust manifold was tolerable. I turned the motor off, and after about 20 minutes, was able to restart the motor, only to have the overheat alarm come on again in about 5 minutes during idling. So I shut the motor down and towed the boat home.

Once home, I pulled all the spark plugs, and checked compression: #1-120, #2-130, #3-130, #4-190. I couldn't figure out why Cylinder #4 was high, until I noticed that whenever I turned the motor over to check the other cylinders, that "mud" (actually, looks like the milky mixture of water and oil that I have seen from outboards with leaky lower units) would spray out of cylinder #4.

I wasn't too worried about a small amount of oil in the cylinder, since I tend to run my gas mixture rich (I have the automatic oil injector, but I also do a little pre-mix with the gas too). I figured I had either a leak in the head gasket or in the manifold exhaust gasket. I pulled the head, and the head gasket looks pretty good - there does not appear to be a source for a leak. But the cylinder head cover had this mud in the bottom area of Cylinder #4 (see picture).
http://i97.photobucket.com/albums/l207/sportjet/1Cylinder4CoverMud.jpg

The inside of Cylinder #4 looked okay, but when I turned the flywheel by hand, mud would come in from the side exhaust ports, into the cylinder. Looking at the below picture, the exhaust port is to the left (facing the picture).
http://i97.photobucket.com/albums/l207/sportjet/2Cylinder4PistonWithMud.jpg

Now under normal circumstances, I figure that the pressure from the cylinder detonation would exhaust the gas out, and water shouldn't be able to come in. Could this "mud" be entering the cylinder through the exhaust port with my compression checking, and also helping "seal" the cylinder (like injecting oil in the cylinder) resulting in the high compression number?

Anyways, I took the manifold cover assembly off, and found all this "mud" as show in the next 2 pictures.
http://i97.photobucket.com/albums/l207/sportjet/3ExhaustManifoldMud.jpg
http://i97.photobucket.com/albums/l207/sportjet/4ExhaustManifoldMudCloseup.jpg

The manifold assembly cover gasket had a thinned out area medial to where I noted a "nozzle" (upper left area from writing in pictures). I thought this area could be a source of water leak. There was not much debris clogging up any water passageways (just maybe 2-3 small pieces of gravel).

But I was not sure what this nozzle did - did it shoot water in or suck water out? And if it shot water in, the direction of the nozzle would force a high pressure water stream right against the inner part of the gasket and could cause premature gasket failure there. I did run a thin wire down through the nozzle, but it seems to enter a space where it curls in the exhaust branch to the drive unit. Here are pictures of the "nozzle" - an overview of its location on the manifold assembly, and a close-up view of the nozzle which has holes on its sides in addition to being open on the end.
http://i97.photobucket.com/albums/l207/sportjet/5ExhaustManifoldNozzleOverview.jpg
http://i97.photobucket.com/albums/l207/sportjet/6ExhaustManifoldNozzleCloseup.jpg

Anyways, I am not sure whether I should just replace the gaskets and give the motor a try (assuming the oil-water "mud" mixture is from water leaking from manifold assembly gasket, and the oil from running too rich), or whether I should just rebuild the motor (which I have never done before).

Also, I am puzzled about this "nozzle", so if anyone has any ideas or knows how it works, I would be very grateful for your help.
Thanks very much,
Jay

 

[Jeff Walkowiak]

Re: Newbie with Sportjet 120, strange compression numbers and

did some critter build a nest up in your ehxaust and cause it to be obstructed forcing water back in to the crank case and in to the bottom cylinder??? I have never seen this before but it sure could be an obstruction time to blow the passages out with compressed air and see what comes out.

 

[gcglastron]

Re: Newbie with Sportjet 120, strange compression numbers and

Thank you for answering Jeff - I'll try that this evening, and let you know if anything comes out! (Girlfriend wants me to take her out to dinner now, or I'd do it right now)...

 

[Jeff Walkowiak]

Re: Newbie with Sportjet 120, strange compression numbers and

be sure to get oil in to the bottom end spray wd40 in the carb lots of it because there will be water on the crank bearings for sure and they will rust

 

[gcglastron]

Re: Newbie with Sportjet 120, strange compression numbers and

Okay, I blew out all the passages with some compressed air, and there does not seem to be any significant obstructions. The branch off the exhaust manifold assembly goes to the jetdrive unit, and I stuck my hand down through there and it seems pretty open (no critter nests).

Thanks for the heads up on spraying the WD40 into the carbs and getting oil in the bottom end - definitely something I need to do since crank bearing rust would be a bad thing :'(. I'll do that first thing in the morning (just took a shower and sleepy now, and I have to take the intake cover off the carburetors). I did run out to the nearest marina this afternoon, taking the manifold assembly, and they weren't sure about the "nozzle" or why I was getting this "mud" in the cylinder. So I figure I'd better read and ask around. I really appreciate your input and assistance Jeff. I'll keep posting what I do and find out.

 

[Jeff Walkowiak]

Re: Newbie with Sportjet 120, strange compression numbers and

the engine is actually a force 120 see what you can learn about force engines I believe mercury bought them out

 

[gcglastron]

Re: Newbie with Sportjet 120, strange compression numbers and

Thanks Jeff. The powerhead is Force/Chrysler. After spraying the carbs and pretty much soaking them inside with WD40, I took a closer look at the gaskets and the manifold assembly nozzle. My guess is the nozzle is to drain cooling water from the exhaust manifold assembly. Also wiped down the mud, and turned the engine over by hand, but could not get any more "mud" out of there. I am wondering if it could have just been a bad gasket. The compression numbers are still puzzling though, so am thinking about that.

 

[Jeff Walkowiak]

Re: Newbie with Sportjet 120, strange compression numbers and

the compression would be high because of the fluid in the cylinder, the big problem is being sure how it got in there in the first place, have the head surfaced if it is warped it may be leaking water in to the chamber, if you don't resurface it it will do it again, water leaking past a head gasket usually leaves a black trail where the gasket mates with the aluminum. you can surface it yourself with a large piece of glass and some 80 grit sand paper glued to the glass but on a straight 4 it takes a big piece of glass and lots of sand paper

 

[gcglastron]

Re: Newbie with Sportjet 120, strange compression numbers and

Sorry I haven't responded sooner, but alas, had the day job that I had to go to! However, I did take the boat and motor to the shop of a good mechanic friend to have him take a look at the cylinders, since I don't know much about what is good/bad. He is guessing that the "mud" is an oil-water mix, from a water leak somewhere. He also agrees with you Jeff, that the water-oil fluid in the cylinder 4 is probably causing the high compression number.

Anyways, we looked closely at the block to see if there was any apparent crack, and the block looks good (ie. NO apparent cracks). We measured the flatness of the head, and found a slight amount of warpage (5-6/1000), so he recommended me having a machine shop hone it flat with strict instructions to take the minimal amount off. The block itself is flat with no warpage. The gaskets for the head and the exhaust manifold themselves didn't look bad, but my friend said that warpage as small as 4/1000 could blow the gasket.

Also, there was a tiny amount of scoring in cylinder 4, which my friend said we should be able to polish out with some very fine wet sandpaper (how fine would you recommend - 800 or higher grit?). I figure I can do that and then reassemble the head and exhaust manifold gaskets, with the proper torques, and give the motor a trial. Hopefully, there is no crack in the block and the honing and new gaskets will solve the problem. I will re-check the compression after re-assembling and let you know what it shows. Thank you again Jeff for your help!

 

[Jeff Walkowiak]

Re: Newbie with Sportjet 120, strange compression numbers and

I would use 220 wet sand paper with oil on it, the scores were probably caused by water removing the oil from the cylinder wall, also the top of the piston will be cleaner than the others if water was getting in the combustion chamber. as for head gaskets leaking , the long 4 cylinder heads are more susceptible to warping. when you get a head gasket see if they offer what is called a low compression gasket, it is basically a thicker gasket and it will compensate for removing some of the metal from the head when it is surfaced. A point of interest napa auto parts sells a lot of marine engine parts, they have a small engine book and you can get gaskets electrical parts etc at very reasonable prices, some napa stores don't even know that they have those parts available.