Which motor to purchase – if any

[jeff-register]

I have no qualms about the 500. All depends on how you look at the motors. Four cylinders are so much smoother running & a guy can start it by the rope. Only issue I see is the isolation dyna floats. Hard to find good ones & there is solid replacements but they tear up stuff. They are easier to me to work on for tune up, just need a timing belt is all. The mag is very dependable too. I would go to a later carbs to have fixed jets too.

[jimaz]

This just popped up on my radar. Guy is local and says it has been stored for 23 years. He bought it 4 years ago but never got around to doing anything with it. He paid $450.00 then. Was a runner when put away. Not sure what to offer. Might still pick up one of those merc’s this weekend, but thought I might get this Johnson as well to start out on given the thoughts I have received here so far. Would be my first motor restored and am determined to do it on my own.

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[lindy46]

I wouldn’t buy it without first checking compression. Even if compression is good, I wouldn’t pay more than $200. But then, I’m cheap and usually don’t pay more than $100 for my old motors.

[lindy46]

By the way, that’s a 1958 Johnson

[jimaz]

What kind of compression numbers would be still okay?

[opposedtwin]

110 and higher is best on the Johnson big twins. check it dry/cold. Numbers could come up a bit after being run but might not too. Look for similar numbers top/bottom. Any more than 5-7 pounds difference and you may have a bad cyl. I’d go for the super sea horse over the jav. 5 more horse, looks to be more complete and quieter.

[opposedtwin]

And yes, no more than $150-$200 even with decent numbers. He was a fool to pay $450. Don’t become his fool.

[jimaz]

Thank you opposedtwin, lindy46. Taking all this very helpful advice in. Will see how it goes. If not, the search continues. No hurry.

[jeff-register]

I believe with the proper service book the 500 is the motor for you. I like the Merc 4 cylinder motors as they have a simple magneto, smaller pistons which make manual starting easy & are so smooth firing every 90 degrees. No battery required & can charge a battery as well. Make sure the gearcase is sealed & no rust. They are fully bearinged for less friction but require clean oil to run on. Everything is easy once you know how & some bolts require some heat to get them out the first time. Be sure to add heat before stripping out the heads of the bolts & be patient. Mercury had no idea these motors would still be in use 70 years later so be easy with them & use good thread anti seeze stuff so they will come out again. You will be awarded!
Good on gas, smooth running & dependable motor when tuned well. The carbs are so easy, just set the floats & jets & align with the other carb. Oh fully bearinged rods, wrist pins, cranks & gearsets. Great design!! And usually plenty of extra HP!

[jimaz]

Well, ended up making a deal for the Johnson after all. The guy was stuck on what he had paid for the motor 4 years ago and did not look like he was going to budge. Then got a text mid Saturday morning that my offer of $200.00 was acceptable after all. Turns out he was only 20 minutes away. While there, tried compression test off a battery. Starter would not budge. Did have a fair amount of bounce when pulling on rope, but recoil seemed gummed up and would just slowly drag back into the housing. Part of that seemed like it had to do with the compression release being fairly gummed up as well and was catching or not releasing cleanly on the return. Did not feel or hear any scraping during pull.
Decided to just go ahead and bring it home. Put together a simple stand for it and got it mounted. Came across a service manual on marine engine site, but not sure if that would be the most detailed one or the best resource for obtaining a service manual. It cover 1946 thru 64 2.5 thru 40 hp Johnsons. Part number 302321_10 for reprints I think???

Also found article regarding waking up a sleeping outboard. As this one has been sitting for 23+ years, thought that might be a good place to start. Have sprayed a little penetrating oil on every exposed nut and screw except ones associated with the powerhead. Will have to put together a shopping list to get started on wakeup including battery, fuel cell and the correct single fuel line for this motor. Which adapter or premade fuel line would work???

Came with controls and wiring harness. Looks pretty rough. Not sure what parts if any are salvageable. Do I need just a simple ignition switch to add to harness for now???

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