Weak Cylinder

[tespejo]

I have a 1961 Johnson Seahorse with a weak cylinder compression. I apparently need new piston and rings according to technician. Other than this problem the motor starts and is good shape physically. I would like to have this repaired but cannot find parts. Is there anyone out there that can help me get parts and hopefully get this outboard run like it is suppose to.

Terry
Prince George, BC
Canada

 

[JB]

Re: Weak Cylinder

Please give us a model number and compression numbers, Terry. We cannot give you good advice without knowing what you are actually dealing with.

My guess is it ain't broke and can easily be revived without a big expenditure.

 

[tespejo]

Re: Weak Cylinder

Model # of 1961 - 18 hp johnson seahorse with weak cylinder if FD - 15 F. Serial # 312869. According to technician compression is 80.

 

[Daviet]

Re: Weak Cylinder

Compression of 80 is not all that bad on a pull start engine, what is the compression of the other cylinder? Are you having a particular problem with the engine. You might try a good decarb and see if it comes up any.

 

[tespejo]

Re: Weak Cylinder

Compression of 80 is not all that bad on a pull start engine, what is the compression of the other cylinder? Are you having a particular problem with the engine. You might try a good decarb and see if it comes up any.

New carb kit installed. New head gasket installed. Motor will not rev to full throttle. Is this piston and rings problem that need to be replaced? If so, are parts still available that you know of.

Terry

 

[JB]

Re: Weak Cylinder

Need compression for both cylinders, Terry. Comparison of the cylinders is the most important part of a compression test. You probably do not have a compression problem. It is more likely to be timing and synch.

Decarbonizing (decarb) has nothing to do with the carburetor. It is a procedure for cleaning carbon from the cylinders and rings, though as Davie says, 80psi is not bad for a pull start outboard PROVIDED that the other cylinder is within 15% of that number.

Under exactly what conditions is the engine unable to reach what RPM (full throttle). Is it in gear? Under load? FW or REV? What prop? This info is critical to making a useful diagnosis.

 

[AlTn]

Re: Weak Cylinder

try marineengine.com for engine diagrams and parts availability...I'm with Daviet, 80 psi. isn't that bad on a pull start...

 

[tespejo]

Re: Weak Cylinder

Need compression for both cylinders, Terry. Comparison of the cylinders is the most important part of a compression test. You probably do not have a compression problem. It is more likely to be timing and synch.

Decarbonizing (decarb) has nothing to do with the carburetor. It is a procedure for cleaning carbon from the cylinders and rings, though as Davie says, 80psi is not bad for a pull start outboard PROVIDED that the other cylinder is within 15% of that number.

Under exactly what conditions is the engine unable to reach what RPM (full throttle). Is it in gear? Under load? FW or REV? What prop? This info is critical to making a useful diagnosis.

The engine will not reach rull throttle in gear and under load. Engine starts and will reach its full RPM just over the start line on throttle. I have brought this engine in the shop here in Prince George, BC, Canada and technician indicates that I need new piston and rings. Come to think of it the service advisor, who seemed rather unknowledgeable, was not quite sure of the problem. I rechecked my bill, where I was charged $ 140.00 CAD for new head gasket did not indicate the compression results. I am going to call them today and get exact readings if they can still remember. Thanks for all the feedback so far.

Terry
Prince George, BC
Canada

 

[boobie]

Re: Weak Cylinder

Pull one spark plug wire at a time when it's running and see if it's firing on both cyls.

 

[bwkre]

Re: Weak Cylinder

I agree regarding the compression. I have the 1961 Evinrude 18hp, same motor and my compression is 80 psi on each cylinder. As far as I'm concerned it runs great. It pushes my 14' aluminum flat bottom to 31 km/hr with 2 people and gear. Sounds like you have trouble but more information is needed to help you. A lot of really smart guys here that can help you out.

 

[tespejo]

Re: Weak Cylinder

I agree regarding the compression. I have the 1961 Evinrude 18hp, same motor and my compression is 80 psi on each cylinder. As far as I'm concerned it runs great. It pushes my 14' aluminum flat bottom to 31 km/hr with 2 people and gear. Sounds like you have trouble but more information is needed to help you. A lot of really smart guys here that can help you out.

I just got more information on the compression of cylinders and according to technician one cylinder reads a 100 and the other is 60. So hopefully this means something to someone because I don't know too much about motors except doing routine maintenance. Anyway, a couple of technicians have indicated that cylinder work is necessary, i.e., replacement of piston and rings. So any kind of suggestions or recommendations would be greatly appreciated.

 

[kbait]

Re: Weak Cylinder

boobie ^ tried to get you to do a cylinder drop test. Start motor in barrel/on lake and have at highest idle in neutral. Pull one spark plug wire. If that wire is firing, and it's spark plug is working, by pulling that plug lead, the motor will react w/lower RPM's. Replace wire and do the other cylinder. If pulling the plug wire on each cylinder causes the RPM's to slow, then your spark is likely fine on both. If by pulling one lead the motor dies, or the RPM doesn't change at all, you have a non-firing cylinder and you need to do a spark test to determine if there is any spark getting to the plug. Use a spark tester and make sure you're getting a 1/4" snappy blue bolt in open air for each cylinder.

These old motors will idle and appear to run very well if firing on only one cylinder, but you'll only get 1/3 speed at WOT.

PERFORM CHECK THIS TEST before you dismantle a perfectly good powerhead! You may have a bad coil, dirty pointset, bad plug lead, bad spark plug or a faulty condenser on one cylinder. Or you could have low compression, which should have been evident by inspection when the head was removed to replace the gasket. Diagnonse and find the exact problem before you make repair plans/purchases..