1957 johnson 7.5hp water in lower cylinderbut still have good compression?

[grave digger]

I a new user to this forum and thought maybe somebody could help me. I have a 1957 johnson 7.5 hp that runs great out of water but as soon as you start it in the water it wants to only run on the top cylinder. upon inspection of the lower plug there was water getting into the cylinder some how? any sugestions??

 

[HighTrim]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

What is the compression readings?

Common problem, with backpressure on the exhaust you are dropping a cylinder. Just because a motor runs on muffs does not mean it will run while under load. Are the coils original/cracked?

May also have a faulty head gasket.

 

[mekkamaz]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

I agree with HighTrim...faulty gasket it is...

 

[boobie]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

Head gasket or exhaust covers and/or gaskets.

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

compression is still 83 in bottom and 87 in top.

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

sorry. coils in good shape will shoot 14 inch spark.

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

sorry again thats 1/4 inch spark

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

how will i know if it is a head gasket or exhaust gasket?? thanks digger

 

[boobie]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

With the compression you have I'd shoot for the exhaust covers.

 

[1946Zephyr]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

Ahhhhh yes. Someone got it right. Good job boobie. I had a motor that had this issue once. It so happened, it was a 1957 Evinrude Fleetwin. It drove the serviceman at the local dealer nuts for a considerable amount of time. He went through the expense of having the head milled and everything and water still got in the lower cylinder. I got it home after I purchased it and a 7.5hp Johnson for parts. Somehow, I thought about pulling the exhaust cover and that is when I found a pinhole that had corroded through the thin aluminum plate, that goes between the exhaust cover and the block. This little pin hole was squirting a nice little stream of water into the exhaust port of the lower cylinder, while this motor was running LMAO!! Since I work in sheetmetal, I just made a new plate and put it back together. Problem solved.

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

so are you saying it is a bad baffle plate? or is there another part you are refering to? Thanks Digger

 

[Mas]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

Yes, he is suggesting the exhaust baffle plate. Be very careful of the small screws that hold the cover on...they break easy after sitting for 50+ years. Once they break, your problem becomes a little more difficult!

Mas

 

[Mas]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

...might want to try using an impact driver...the old type used with a hammer.

mas

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

thanks for the advice!!!! I will try that and order the part. should I be able to find that part here on iboats? or where should I go? Thanks Digger

 

[1946Zephyr]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

If you can't find it, they're easy to make. Stainless might be a good option, vs. aluminum.

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

Well got to take the exhaust cover off today to get to the baffle and when I did I come to find out the baffle looks good no pin holes that I can see and not rusty or anything. could it be the head gasket? and when I put the baffle back in should I use a gasket sealer?Thanks to all that have given suggestions please dont stop. I want to get her running good. Thanks Digger

 

[boobie]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

Make sure you put new gaskets on and use something like OMC gasket sealing compond on them. You may have missed it but an exhaust cover gasket could have also caused the prob.

 

[1946Zephyr]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

Yea, now it most likely is the head gasket or water jacket surrounding that cylinder. You might have the head checked for flatness.

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

Ok. I will check head gasket as soon as the new one I ordered gets in. Thanks for the input. Digger

PS: will keep u posted.

 

[grave digger]

Re: 1957 johnson 7.5hp water in lower cylinderbut still have good compression?

does anyone know the torque and order for the head when I replace the gasket??? Thanks Digger