Trying to evaluate an old Johnson 50hp

[coreyrosenfeld]

I want to see if the old Johnson 50hp motor I bought with my boat is running. I have built a nice stand using tips from the forum and will have the motor on it tonight. Now, the lower unit is missing the lower part of the housing and the gears are out of it as well. I know I will have to replace with a new lower unit anyway. <br /><br />Can I try to start this thing without the lower unit working to see it it will start? What things should I look for in this stage to help evaluate this motor to see if it is worth working on. <br /><br />Also, what do I need to do a compression test and how is this done.<br /><br />Thanks

 

[Chinewalker]

Re: Trying to evaluate an old Johnson 50hp

Hi OC,<br /> There's no reason why you can't fire it off with the lower unit removed. Keep in mind that the motor will have no load on it, so keeping the RPM below 2000 is a must. Also, you've only got about 30-45 seconds before the motor will start building up enough heat to be considered "hot", so run it for short periods only and allow it to cool completely after running before starting it up again.<br /> One other thing - I find that sometimes large motors, when started off the boat without the steering, etc. hooked up may try to spin away from you. The torque of the motor will make it want to turn and on a less than substantial stand it may want to fall over. I recommend that you have a helper with you to hold the motor from turning, keeping his/her hands free of all moving parts in the process. With the unit off, you'll not have a spinning prop to worry about, but there's still plenty to keep yours eyes on and hands off....<br /> Start with compression. Get yourself a compression gauge from Sears or NAPA - should run you less than $30.00 for a decent one. Check all four cylinders - you want them even across the board with no more than 10% variance between them. Check for spark. Good, hot spark will jump a 1/2" gap.<br />- Scott

 

[phatmanmike]

Re: Trying to evaluate an old Johnson 50hp

connect a garden hose to the water pickup tube with a hose clamp, then you wont have to worry bout burning up your motor.<br /><br />better safe than sorry

 

[coreyrosenfeld]

Re: Trying to evaluate an old Johnson 50hp

Ok, I guess what I need is a quick class on the basics of how these motors work. I have the clamp thing that has the female end of the garden hose in one side.(It came with the boat and I had no clue what it was.) What size battery will I need for the boat? I will have the standard lights and a troling motor. Should I get the dual purpose cranking/deep cycle? What size?<br /><br />Thanks

 

[coreyrosenfeld]

Re: Trying to evaluate an old Johnson 50hp

Oh, where do I hook the clamp to? Where is the water pick up tube?

 

[angus63]

Re: Trying to evaluate an old Johnson 50hp

Factory manuals can be found at<br />www.theoutboardwizard.com<br />Judging from your questions and your interest to work on this yourself, first thing to do is get the manual. It will be a few bucks well spent. Sometimes ebay has used ones also.<br />Good luck

 

[Solittle]

Re: Trying to evaluate an old Johnson 50hp

Old Cobia - Best bet at this point for you is to find a friend (or make a new one) who knows a little bit about these motors. Sounds like you are starting from ground zero as we all did at one point and it is great to have a mentor to get you started. Feel free to post of course but you will save a bunch of time by having someone looking over your shoulder.

 

[R.Johnson]

Re: Trying to evaluate an old Johnson 50hp

I thought of something when reading the above post's about moving the engine around, and getting it on a stand. That engine had a tilt assist to help tilt the engine when on the boat. Now that the engine is off the boat, that entire transom mounting bracket is in the lock down position. The tilt assist was a coil spring wound from either 1/4", or 5/16' square stock spring steel. As you can imagion, that spring stores tremendous force when wound, and locked down. What ever you do! do not trip the tilt release when that engine is off the work stand, or off the boat. To do so will let that entire mounting bracket fly forward with enough force to cause serious injury, and I mean SERIOUS. If it struck you in the face, you would be lucky if it did,nt kill you. That thing was a real BOOBY TRAP when locked down, and off the boat. I wish I would have caught this sooner.

 

[coreyrosenfeld]

Re: Trying to evaluate an old Johnson 50hp

Thanks for the warning... The motor is on the stand now and IS in the locked position! Thanks...

 

[R.Johnson]

Re: Trying to evaluate an old Johnson 50hp

This is one post where I,m really glad to see the owner respond. Be carefull also with the motor on a workstand. With the gearcase off, it could over-balance, and fall forward.