Rebuilding a 1976 15HP Johnson

[DaveInGA]

What does it take to rebuild a 1976 15HP Johnson from top to bottom and do it right?

I'm talking separating out each section of the motor, disassembling it, cleaning it, going through it and replacing things that need to/ought to be replaced after a motor has been around 31 years.

What all should be bought for the powerhead, for instance? This motor is at 80 PSI compression and is very hard to start. It's been decarbed per the procedure on the board and has the following new parts installed: New plugs, new starter rope/spring, new impeller. A spark tested showed both cylinders to be getting excellent spark. The carburator seems to be in good shape.

Thanks,

Dave

 

[HighTrim]

Re: Rebuilding a 1976 15HP Johnson

there are a couple threads you should read, go through them then come back and post your results, the experts on here will help you after that, gl

http://forums.iboats.com/showthread.php?t=158086

you didnt say whether you could start it up or not, but this will help

http://forums.iboats.com/showthread.php?t=158071

 

[DaveInGA]

Re: Rebuilding a 1976 15HP Johnson

Yes, I can start it and get it to idle. I've already went through the awakening a sleeping outboard and decarb process. I'm getting good fuel and good spark. The rubber thrust bushings are worn out and it "clunks" when moved. The compression measured in both cylinders is right at 80 PSI when measured with a brand new gauge.

Plastic knobs, etc. are old, rotted and keep breaking and rubber gaskets such as the lower motor cover gasket, etc. are falling apart. The lower gearcase is leaking oil. The motor, even after having a can of seafoam run through it per the decarb instructions, still smokes if revved any at all. Plugs are getting fouled even though the fuel mixture is correct and the carburator idle has been properly set. It's not running rich or lean and will idle.

In other words, the motor is plainly worn down to the point it needs rebuilding.

 

[tashasdaddy]

Re: Rebuilding a 1976 15HP Johnson

Dave, other than necessary gaskets, there is no way to tell what you need to order, until you get into it. be sure to have the correct Johnson manual for it. not an aftermarket.

 

[DaveInGA]

Re: Rebuilding a 1976 15HP Johnson

tashasdaddy,

Do you think it might be worth putting a carb kit into it before starting on rebuilding it? That's about the only thing I haven't done related to tune up.

 

[iwombat]

Re: Rebuilding a 1976 15HP Johnson

I think I'd just be double checking the choke plates to make sure they're opening up all the way.

80 is on the low side, but one gauge's 80 is another gauges's 110. Do you have any way of calibrating that gauge? Another motor maybe?

You can gasket and re-ring a 15hp for around $120 or so. You might need new pistons and a bore if it's out of spec though. That would probably pile on another $100 or so. But, if you've got enough wear to warrant a re-bore, you probably want to replace the rod bearings at a minimum - add some more $$.

Have you inspected the exhaust tube? Those motors have a tendency to build up _a lot_ of carbon in the tube. That could be causing some of the symptoms you describe. (My last 15hp had a nearly closed exhaust tube.)

 

[DaveInGA]

Re: Rebuilding a 1976 15HP Johnson

iwombat,

Thanks for the information. I'll check out the things you've mentioned. I need to tear it down a bit to see where things are anyways.

Unfortunately, I don't have a way of calibrating the gauge. It is a new gauge though, dunno if that's good or bad.

I'm thinking right now if I can get what I want out of it, I'd be better off to either sell it or go for a full rebuild, whatever that means. I've never been one for compromise measures. I'd rather do it "right" the first time and not go back into an engine later. If not, I'd rather just get rid of it.

Dave