Johnson QD-15 '54 10 hp blown head gasket?

ExxWhy

Seaman Apprentice
Joined
Oct 31, 2009
Messages
49
I didn't get too far with this project before I have a question. 1954 10hp with unknown history. Ran when parked 10+ years ago. Looking to get it running to use, so plan on a complete tuneup with new coils, points, carb kit , water pump, fuel pump mod etc.

First thing, checked the compression to see if it was a viable candidate. Top cylinder 75, bottom 15. Sprayed more oil in the plug hole, now I have zippo for compression. Hmmm, not good.

May as well pull the head and see what I see. Expecting burned piston or badly scored cylinder. It all looks OK to me, but the head gasket looks very suspicious. As circled in the picture, there is a section that looks blown out to me. Also some blackness on the cylinder top surface and some darkness in the water jacket. Suspecting the head gasket is blown and was going last time it was running. Sitting for 10 more years didn't help it. Head bolts were fairly snug all the way out as if they had not been turned in 55 years, so guessing it may be original. Maybe not, but the gasket is OLD. It is making pressure in the crankcase when I turn it over as I get a little puff in the cylinder when I turn it over with the head off. Cylinder walls feel OK, the picture makes it look worse than what I can feel. Actually, the bottom cylinder looks a bit better to me than the top that had decent compression. Seems like the proper amount of play in the piston at the top, not too sloppy, not too tight. All in all seems to me like it should have compression with a new gasket. But, this is the first outboard motor I have ever taken apart, so I wanted to get a second or third opinion before I dump money into it. ($200 or so in parts for everything, well worth it if it's a runner, not so much if it needs more.)

One last question. When installing the new head gasket, it should go on dry or use some sort of gasket compound?

Take a look at the pics and let me know what you think.

Many thanks,
Eric

QD15-1.jpg

QD15-2.jpg

QD15-3.jpg
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: Johnson QD-15 '54 10 hp blown head gasket?

Definitely looks like the gasket let go. Get a new one (I think they've got them here on Iboats) and see what happens! Head gaskets go on dry. Make sure the head and cylinder block faces are clean.
 

ExxWhy

Seaman Apprentice
Joined
Oct 31, 2009
Messages
49
Re: Johnson QD-15 '54 10 hp blown head gasket?

Sounds like a plan. I guess it was the plan all along. :)

Interesting and ambitious boat projects you have there Chinewalker.
 

samo_ott

Vice Admiral
Joined
Jun 18, 2006
Messages
5,125
Re: Johnson QD-15 '54 10 hp blown head gasket?

Yep, I would just get a head gasket and install and then test the compression again. If it's not good, dont get any new parts!
 

1946Zephyr

Vice Admiral
Joined
Oct 21, 2008
Messages
5,556
Re: Johnson QD-15 '54 10 hp blown head gasket?

Good motors and are relatively easy to coax back to life. You can also remove the bypass covers, to see the condition of the pistons too. If they don't appear to have any scoring, then it's likely they're in decent shape and ready to rock and roll. Incase you're wondering what bypass covers are, they're the two little plates on the side of the engine block, located about where the bottom of the stroke is. I would at least get it running and run it for a little while, before you'll be able to get an acurate compression reading. Typically, a motor that has set for many years will have rings and grooves that are slightly sticky. Running the engine will get good lubrication worked in around the rings and get them flexing better. Open the throttle all the way open and try your compression test again.:cool:
 
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