Moisture on #4 cylinder reeds

[sschefer]

I just discovered moisture on the reeds on carb side of # 4 cylinder on my 91 Mariner 100. This is the only cylinder with that shows signs of moisture on the reeds. I am running a water separator and have tested the fuel for moisture and there doesn't appear to be any.
The reeds are all laying flat against the blocks and cylinders 1, 2, 3 all look fine.

On the water, acceleration to 4000 rpms is great but after running a few minutes I begin to get a rattle. If I back off the throttle the rattle subsides and I gently bring it back to the dock.

My suspicions are that the thermostat is opening and water is getting into #4 cylinder. I think the mositure I see is being blown back through the reeds and collecting on the outside of the reeds.

Have any of you mechanics seen this before? I'm thinking exhast plate gasket or possibly a blown head gasket.

Thanks in advance for any insights you might have.

Steve

 

[j_martin]

Re: Moisture on #4 cylinder reeds

I just discovered moisture on the reeds on carb side of # 4 cylinder on my 91 Mariner 100. This is the only cylinder with that shows signs of moisture on the reeds. I am running a water separator and have tested the fuel for moisture and there doesn't appear to be any.
The reeds are all laying flat against the blocks and cylinders 1, 2, 3 all look fine.

On the water, acceleration to 4000 rpms is great but after running a few minutes I begin to get a rattle. If I back off the throttle the rattle subsides and I gently bring it back to the dock.

My suspicions are that the thermostat is opening and water is getting into #4 cylinder. I think the mositure I see is being blown back through the reeds and collecting on the outside of the reeds.

Have any of you mechanics seen this before? I'm thinking exhast plate gasket or possibly a blown head gasket.

Thanks in advance for any insights you might have.

Steve

Pull the plugs and have a peek into the cylinders. If water gets into a cylinder, by whatever means, it will be super clean. It should have a little carbon and oil in it.

hope it helps
John

 

[sschefer]

Re: Moisture on #4 cylinder reeds

Pull the plugs and have a peek into the cylinders. If water gets into a cylinder, by whatever means, it will be super clean. It should have a little carbon and oil in it.

hope it helps
John

Thanks John,
I'm pulling the powerhead off tonight. If there is no indication of a problem at the exhaust plate then I'll pull the head off.

I have my suspicions but I'll hold back and see what others say so I don't get folks thinking in my, often wrong, direction.

 

[BR]

Re: Moisture on #4 cylinder reeds

Steve,

Check your crank seals on the lower end cap. That's what did my 4 cyl. 850 in. The rattle you hear may be your upper main crank bearing. Be prepared to replace that too as it gets lubrication oil from base of crankcase via the thin hose connecting both. When #4 is getting water it doesn't take long for upper bearing to lose lubrication.

Good Luck!

 

[sschefer]

Re: Moisture on #4 cylinder reeds

Thanks BR.. I just ordered a new set of gaskets for it. I'll pull it tonight and get it on a stand. I was just going to lift it and change the Exhaust plate gasket but now I think I'll just tear it down and rebuild it. I have a machine shop within a couple of miles that than can check these blocks for cracks.

I'm in no hurry, I already made my annual fishing trip and I have a new F-150 Yamaha that I can slap on it. I'm selling this boat with the mariner motor this winter. I'm fixing the mariner because I won't sell it if I know it has a problem.

 

[sschefer]

Re: Moisture on #4 cylinder reeds

BR, I think you nailed it. The connector tube between the water pump and the water tube in the L/U was split down the side. It looked normal when the L/U was off but when I put a little pressure on it, it slipped off to one side.

My unproven theory (aka best guesstimate) is that because this engine has a high volume water pump it filled the l/u first and when it built up enough pressure the water went up the tube and cooled the engine. That would explain why the pee tube looked normal. The water in the l/u was probably clear up to the bottom of the lower main seal on the power head and it was slinging water into #4.

Anybody ever seen or heard of this before?

 

[sschefer]

Re: Moisture on #4 cylinder reeds

O.K. I think I'm finally getting to the bottom of this and it's multiple problems.

The exhaust plate gasket was definitely leaking. There was a carbon layer throughout the entire plate casting. But there was also a oily waterline on the bottom of the block casting at the lower main cavity area.

There is no readily apparent water in the #4 cylinder and the fuel oil mix that came out of the lower main and dumped into the #4 piston when I layed the power head over is not water contaminated.

#4 Rod bearings appear a bit cleaner than 1,2,3. That's concerning to me so I'll pull the crankcase cover off and have a look at all of the seals. They'll get replaced even if they aren't bad.

Does anybody want to see pictures of a torn down 100hp mariner?

 

[RaScLeS]

Re: Moisture on #4 cylinder reeds

yes i would