Sport Jet 90 leaking exhaust gasket?

[RedBarron55]

My new to me Hobie Jet has a problem with water getting into #3 cylinder even when the dealer adapter is purttng out low flow.
It may have also let water in when I had the boat in the water last weekend and I wonder if the gasket may have been damages by running it out of the water either by me or the previous owner?
It seems that with even a very small water output the water can get into the cylinder.
Is this normal?

 

[Speedling]

No, you don't want water in the cylinder.
Check how the water goes into the exhaust and engine block and be sure nothing is obscured. If there is a blockage in the exhaust it can back up into the cylinder through the valves.
Or, it could be head gasket.

 

[Cobra Jet Steering LLC]

Water inside the engine will be the kiss of death to your rings cylinders and bearings I wonder if you already damaged the engine I have a fer things that you can check but I am breaking my rule of no posting B C so I need to stop posting now and post it A C

 

[Cobra Jet Steering LLC]

Ok I believe we have already discussed that you own a Force 3 cylinder 2 stroke vertical outboard power head, back when we discussed the electrical system.
Your engine operates with 3 float style carbs not diaphragm type that other 2 stroke engines use. Those are also an issue and I believe you already addressed that part.
Also be very careful of the spark plug wires as those deteriorate inside the coating and actually loose the core wire over time Usually requiring new solid wire plug wires that can be replaced without replacing the coils if you know how, I do, so if that becomes an issue your engine will run good when cold but start dropping a cylinder and miss real bad after a minute or two of running. You will keep blaming the carbs but in fact it is the plug wires. To see if they are corroded remove the plug end and you will see the core wire, pull on it with some needle nose pliers if the wire is good the core will not budge if it is bad the core will just pull out without resistance and after a short piece comes out it just disappears.

Now to address the water in the engine, the power head gets hottest at the top "heat rises" and if it overheats the top cylinder usually blows a head gasket and if that happens the HEAD always WARPS and will need to be surfaced or it will just keep blowing them. A sign of overheating is the color of the paint on the head it will darken and a sign that someone had a over heat issue can be that the engine is freshly painted to conceal the discoloring of the paint. Also while on the color change topic if you pull your head from the block look in the narrow areas of the head and if you see a darker color in certain places this is an indicator as to where the head gasket was leaking and where the head is warped, as you surface the head to reinstall it be sure all the dark spots have been removed from the head as this will indicate the head is flat again. To do your own head resurfacing use a heavy piece of glass with 80 grit sand paper glued to it and move the head side to side on that sand paper for an eternity " or slightly shorter time that still feels like an eternity until the entire surface is all shiny. I actually built special Jeff surfacing machines to accomplish that because it was so time consuming and tedious, I still have a small version of the one I made for a friend of mine about 30+ years ago.

To check for water damage inside the engine , remove the spark plugs and first look at the tips, they should be chocolate brown if you see silver or grey on them that is a sign of water inside the combustion chamber during operation also if you notice the gap keeps getting closed on a particular plug that is a sign of play in the connecting rod from bearings going bad. Real bad if that is happening!
So with the plugs removed rotate the flywheel and watch the top of the piston through the plug opening it too should be chocolate brown if it is clean you can bet water is inside the combustion chamber removing the carbon from the top of the piston and eventually removing the aluminum and depositing it on the cylinder walls where it will cause ring seizure.
After you see the top of the piston rise to the opening while rotating the flywheel slowly you will see it start to go back down, when it does STOP rotating the flywheel and use a screwdriver to push down on top of the piston via the plug opening, if you feel it make a clunk your rod has bearing issues, if it is tight and no clunk it is ok.

 

[RedBarron55]

Thanks for the reply and the information.
I have checked the compression cols with a not fully charged battery and get 95 PSI on all cylinders. This sounds a little low to me, but cranking speed may make a difference.
I washed out the cylinders with WD40 and sprayed some in the intake while spinning over the motor.
I also put a little 2 cycle oil in each cylinder and spun the engine to spread it around.
Putting the plugs back in after blowing the clean and it did start and idle OK now with the carbs cleaned and reinstalled.
I just hope that the water has not started corrosion in the bearings and it has not broken a ring etc.
Fingers crossed!
It sounds OK, but who knows.
The engine has not run enough to discolor the paint and it looks new.
I really don't want to pull it apart if I don;t have to.
On another note I took my genuine Harbor Freight oscillating saw and cut the flange on the left side at the flotation box so that I could see how it was installed.
As I suspected the boxes were attached to the hull with polyester mat and they have peeled off the hull side and are stuck on the box.
When I cut parallel to the box towards the hull I could remove the tabbing and see the joint open so that the water I saw when I bought the boat had to have run into the foam area.
When I have uploaded the pictures I took I will add them here.
As you can see from the picture the tabbing is loose from the peeled top to the box and there is no barrier to water entry.
I plan to cut the tabbing completely away and remove the boxes and pull the foam.

 

[Cobra Jet Steering LLC]

The fact that you have the same reading of compression on all 3 cylinders is a good thing Usually your top cylinder will be lower if you have a bad head gasket

 

[RedBarron55]

The only thing I know to do is proceed with fixing the boat.
I am concerned that if there is excess weight in the rear the boat might sit lower and if there is a bad spot in the exhaust manifold and gasket water will leak into the lower part of the chamber and flood the #3 cylinder.
The same thing with the boat on the dealer adapter out of the water.
Is there a good drawing of the cooling system so that I can see better how the water comes in and what it takes to get into the cylinders?

 

[Cobra Jet Steering LLC]

They have not made those engines for a long time so look on the web and see what you can locate Also look for a service manual from Climer publications

 

[RedBarron55]

Thanks Jeff.
I have a PDF file of the factory manual, but there is not a good picture that shows the water flow.
I have found something on a 4 cylinder Force outboard and it seems to show me that the water comes in the bottom of the exhaust chamber and through the block and to the head and then over board. I assume down through the exhaust, but this is where I get lost.
I can see where the water can come up and over the exhaust elbow and into the bottom of the expansion chamber, but I don't see how the cooling water gets there unless there is a leak from the cooling side of the exhaust to the exhaust side.
This is not for the Sport Jet 90, but is close.

Re: Water flow diagram

In the diagram you are looking at the cylinders with water flow to the old style thermostat which was located at the very top of the head and water only flowed down a cast in tube.

In the diagram, Left part is the exhaust chest, middle is the cylinders, and right side is the head.
This diagram is for an old Force outboard and the difference is that in the Sport Jet the water comes in at the lower left from the jet pump tap, from what I can determine.

 

[Cobra Jet Steering LLC]

That is something I never had a reason to explore so I can't be any help on that one

 

[RedBarron55]

I have ordered a gasket and I will take the exhaust manifold off and see what is going on if anything.
My guess is that the exhaust heat might burn the gasket and create the leak from the water side to the exhaust side.
If the engine were producing power and had pressure in the exhaust system that as higher than the water side you are OK, but if not then the water would enter the exhaust side.
Especially if the engine is turned off and the cylinders and exhaust cools might the suck water in (maybe)

 

[Cobra Jet Steering LLC]

I really doubt you actually have any leak in the exhaust system as long as the exhaust is exiting properly the water should be exiting also ,actually on that engine you do not even need to run the engine while you flush it on the hose . Your engine does not have any water sitting in it after you use it unless something is plugged up it . It drains itself via gravity.

 

[RedBarron55]

Thanks, but I was running the engine to check it out.
I have a bunch of things going on and the #3 cylinder getting water when running is a real pain.
Last Saturday I put the boat i the water to check it out and had problems with the starter Bendix and probably the fact that there was some water in the #3 carb and less in the #2 but the it also feeds the enrichment valve.
I have ended up getting water in the cylinders at least once because of having the water flow from the hose too high and being hooked to the small flush line that goes to the thermostat housing.
I cleaned the motor out and built an adapter for the main hose, but sill must have had too much flow, I don't know, but I am worried about the flush hose and the cylinders!
I have the gasket coming really because I saw a post from a guy with a 120 4 cylinder that had similar problems filling his #4 and he found a blown out spot in his gasket.
I do notice exhaust gas coming out of the hose if I start the engine with it disconnected, but this could happen either way I think, leak or not.

Thanks for the help

 

[Cobra Jet Steering LLC]

exhaust coming out the hose with the water off is normal, exhaust shares the same space as the water as for getting water in the cylinders I wonder if there is an obstruction where the exhaust exits causing the water to be pushed into the cylinder hard to say .

 

[RedBarron55]

The water seems to run out of the bottom OK.
I don't know how to check.
Does the water just run into the exhaust?
Where does it go after it passes the thermostat?
Or more likely do I still not have a good understanding of the flow in the Sport Jet?

 

[Cobra Jet Steering LLC]

It's an outboard power head , the jet pump supplies water to the water jackets but it has no water box so the water and exhaust exit the bottom of the boat the thermostat just regulates how much water gets into the water jacket, when you disassemble the water jacket cover you may find a lot of sand inside it I have seen water jackets with a lot of sand in them from people running through shallow water and sucking the sand into the jet thus that sand gets put into the cooling jackets. I can not see how it is getting into your cylinder unless you have water in your fuel system or water in your fuel filter but that really does not make sense as the fuel comes from the bottom cylinder upward so the bottom carb would get the water in it first if it was in the fuel system.

 

[RedBarron55]

The water might have gotten in early from the tank, but now if I pump a sample into a clear glass jar it is clear with no water.
I suspect that the carb issue is over with cleaning them out and dumping the water that was in the lower bowls.
Remaining is the separate issue of getting water in #3 cylinder.
I like to have parts in hand before I remove the exhaust manifold.
I know the water flows in the bottom of the exhaust manifold and around the exhaust and into the block and head.I still wonder just what is the reason water gets into the exhaust chamber?
I know that the exhaust goes up the loop to prevent the water from outside the boat from getting back into the expansion chamber.
I wonder where the cooling water escapes the engine and how it gets down to the outside ( I assume in the baffle under the boat.
Why are these motors so sensitive to the flow and pressure of cooling water coming in via the hose from the pump?
WHATUPWITHTHAT?
I found a couple of pictures of the manifold and here they are:

If any water gets in here it goes right into the #3 cylinder ports and OOPS!
As an aside when I put the boat in the water and ran it a bolt about half way up towards the inside row front of the manifold was leaking water. I put a little gasket sealer on the bolt and tightened it up and stopped the external leak, but inside who knows?

 

[RedBarron55]

I looked at the manifold bolt I found leaking when I put the boat in the water and ran it and is is the one that is right in the middle of the large opening at the inlet to the exhaust elbow.
On the picture above it was the 4th bolt from the right right in the middle of the exhaust port where all of the exhausts come together.
This would probably be the hottest spot and the only way for the bolt to leak water is for the gasket to be leaking between the cooling plenum and it is easy to see that it is just as likely for the water to continue into the exhaust and then into the cylinders.
If I understand the system the water should be isolated from the exhaust completely and the path should be from the hose at the bottom through the block and head and then (I think) through the outlet in the base plate to the chamber under the engine where the exhaust joins it from the bellows.
It would be difficult to think that other than a major blockage here for water to back up through the bellows to the exhaust manifold.
My OPINION is that the exhaust gasket is easily burned through with no cooling water to keep the temperature low enough for it to survive. Tomorrow I am going to try pulling the manifold to inspect for a leak in this area.
This explains why water gets into the cylinders on the hose!
I will post pictures either way.

 

[Cobra Jet Steering LLC]

sounds goo

 

[RedBarron55]

I got the steering parts today.
Looks good.
Thanks.
I think I may drill the holes and trial mount, but leave them off for when I get the boat going so that I can do as you say and try before and after.
Thanks again