15 hp Johnson(long)

[Cobra Pilot]

I have been trying to get an old outboard running that has been sitting up for 5 years. The motor is a 1986 15 hp electric start Johnson. I have rebuilt the carp. replaced the plugs, fuel lines, and fuel tank. I have changed the oil in the foot (it was clean) and rebuilt the water pump. The fuel pump works and the compression is around 85 on both cylinders. The motor will run for 15 to 20 seconds. Here is the problem, during the cranking and running phase the engine will lock up and I have to rotate the flywheel backwards to free it up. It will even lock up when you are cranking it with the plugs out.I tried poring Marvel Mystery Oil in the plug holes and letting it set for a week, no change Any ideas?

 

[Joe Reeves]

Re: 15 hp Johnson(long)

Remove the lower unit. Remove the spark plugs. If engine still locks up when cranking, you have a serious internal powerhead problem. But first, perform the following test.

(Piston Play Check)
(J. Reeves)

This procedure will tell you if there is any wear or play in the Wrist Pin, Wrist Pin Bearing, or Connecting Rod to Crankshaft area.

Remove the spark plugs. Insert a screwdriver, dowel, punch, or some object of your choice through the s/plug hole and into the cylinder/piston area. Hold the tool lightly against the top of the piston. Turn the flywheel by hand, bringing the piston up to top dead center, then continue turning the flywheel to pull the piston down about a inch..... all the while holding the tool lightly against the piston top.

Now, at the point whereas the piston has been dropped down about a inch, grab the flywheel and hold it firmly. Now, push that tool solidly and firmly against the piston top.

If the piston moves without moving the flywheel, there is a problem (wear, play, clearance, etc) somewhere with the items mention in the first sentence. Be sure to check all of the pistons/cylinders.

 

[Cobra Pilot]

Re: 15 hp Johnson(long)

I can feel no play with either cyclinder.

 

[Cobra Pilot]

Re: 15 hp Johnson(long)

I dropped the lower unit and it was still binding. I than removed the plugs and squirted MMOil into the carp. Cranked it over and metal filling came out the plug holes with the MMOil. Bad news!

 

[tx1961whaler]

Re: 15 hp Johnson(long)

Bad news!

Yes. Bad news. Pull the cylinder head and check the damage. Pictures would be helpful.

 

[Cobra Pilot]

Re: 15 hp Johnson(long)

I don't feel comfortable taking this engine apart myself. I think the problem my be the upper rod bearings but of course I am not sure. My question is would I be better of paying someone to repair this motor or selling it for parts? All the other parts seem fine.

 

[tx1961whaler]

Re: 15 hp Johnson(long)

You may just be able to get a rebuilt or used power head. It's not a huge job to do on a small motor; mostly part swapping from the old to the new.

For me to decide, I'd use the following points:
1. Does the motor have sentimental value?
2. What is the cost of a new motor?
3. What is the cost of a comparable running replacement motor?
4. How much does it cost for a professional shop repair?
5. How much for a DIY repair?
6. What is the overall condition of the rest of the motor? (e.g. beating a dead horse?)
7. What is the part-out value?

 

[Whoopbass]

Re: 15 hp Johnson(long)

Part it out on Ebay.
You have a solid $500 in parts.

15 hp carb $100-175
lower unit 125-175
complete electric start assembly 150
pull start 40-50
transom bracket 30-50
prop 25-35
cowl 10-40
Miscellaneous parts 50-100