1974 15hp 2 stoke engine - Head Gasket / Electrics

[Calibra]

Hi

​This is for a mate of mine and I am just trying to help him out.

​He took his boat out and after 30mins, the engine died. He started it and it ran as if the fuel pump had failed.

​Fast forward 4 months...

​He brought it round to my place, and I've found the following issues

​1) Compression in the lower cylinder is now 100psi, while the top one is approx. 130psi - 6 months ago they were the same.
​2) When pulling on the cord to start the engine, neither spark plug works (Tried new ones)

The engine isn't seized and moves fine without any issues

​I've decided to look at the powerhead first and then the spark issue.

​1) Do we have to remove the powerhead from the leg in order to do a head gasket?
​2) How do you undo head bolts when they are stuck in solid?

​For the electrics, is it possible to swap them out with a newer engine? Say from 1979 onwards?

Condition of spark plugs shown

Thanks

James

 

[Newyota]

As far as spark make a duel spark checker out of a block of wood and two 1/4 inch bolts and a piece of aluminum and and a ground strap.I just did that for my 9.9hp Johnson.Too hard to really see and check spark with the plugs.I thought I had no spark and when I did the test I could see I had great spark.Do you have a kill switch that could be bad?They run on an open circuit on my motors and ground out circuit when pushed.Never pulled the head.

 

[oldboat1]

Head cover comes off without additional disassembly, but a little trick on that motor. Clearance is tight at the bottom, so the bottom bolts need to be backed out but left in the cover when the cover is lifted out.

 

[thumbnut]

Head cover comes off without additional disassembly, but a little trick on that motor. Clearance is tight at the bottom, so the bottom bolts need to be backed out but left in the cover when the cover is lifted out.

The trick is to put the bottom bolts in the head before installing the head. I put the head on with upper bolts and had to start over to get the bottom ones in first. no big deal but...