1964 Johnson 18 HP compression??

[oldfarmall]

Hello-

I am in the process of fixing up an old Johnson Seahorse 1964 model 18 HP. This motor has not been run in for about 10 years. It ran good the last time we used it, but the lower unit went bad and it was put in the shed ever since. I have now got a good lower end for it, and am in the process of getting it going. I have not attempted to start the engine yet. Did a cold compression test by pulling the recoil a few times. I got 70 pounds on each cylinder. Is this good? Also, with the spark plugs in place it seems to have great compression when trying to crank over. What should the compression psi be with a warmed up engine for this model? Any thoughts would be great. Thanks!


Jesse

 

[asdasc]

Re: 1964 Johnson 18 HP compression??

Hi and welcome!

Those numbers seem a little bit low, but as long as they are similar you are fine. It could be low just due to the speed you are turning it over and lack of lubrication, build up of carbon, etc.

Do yourself a HUGE favor and look in the Top Secret information at the top. It is really a list of frequently asked questions. There is one in there called awakening a sleeping outboard. That will take you thru all the things you need to check and do before starting the motor to make it good without doing any damage to the motor.

The 18's are GREAT motors, so get it running and enjoy it!

If you can't find the information there, let me know and I will post a link.

 

[coolguy147]

Re: 1964 Johnson 18 HP compression??

ya thats right on the border line. id say go ahead check spark then change impeller and clean carb and so on

 

[jbjennings]

Re: 1964 Johnson 18 HP compression??

My 50's and 60's 18hp OMC outboards that run good have between 115 and 125psi. I suspect an incorrect measurement or inaccurate gauge (common). Usually when there's compression that bad, there's one cylinder that's a lot different from the other. At least, that's my experience. I'll bet your motor is fine.
JBJ

 

[thbtgold]

Re: 1964 Johnson 18 HP compression??

Does anyone know where to get rebuild parts (pistons etc) for a '59 18hp?

Hi and welcome!

Those numbers seem a little bit low, but as long as they are similar you are fine. It could be low just due to the speed you are turning it over and lack of lubrication, build up of carbon, etc.

Do yourself a HUGE favor and look in the Top Secret information at the top. It is really a list of frequently asked questions. There is one in there called awakening a sleeping outboard. That will take you thru all the things you need to check and do before starting the motor to make it good without doing any damage to the motor.

The 18's are GREAT motors, so get it running and enjoy it!

If you can't find the information there, let me know and I will post a link.

 

[asdasc]

Re: 1964 Johnson 18 HP compression??

BRP still makes them. In order to get the parts you need, you will need to know the original part number and type it into a retailers website such as this one. You will need a parts manual.

Marine Engine

Pistons are 377262 for a 1958, but I am fairly confident they are the same.

 

[crxess]

Re: 1964 Johnson 18 HP compression??

Pull the plugs-Tilt the motor, plug holes up - level the pistons - fill with Marvel oil or PB Blast and let sit over night.

Get it running and do a de-carb. may have stuck rings after sitting all that time.

 

[ozarkzander]

Re: 1964 Johnson 18 HP compression??

I just picked up one of these myself FD18E off of craigslist for $125. It was too heavy for the boat he had it on and wanted to pull the rear end under water when it got too much gas. the compression on mine was 90 lbs in each cylinder. I'm going to do all of the things listed here to awaken a sleeping motor since he hadn't "ran" it other than showing me that it works in a year. There is a place for a starter on this that I am thinking of taking advantage of. I have the parts catalog coming to me in the mail right now, so we will see.