Compression Question...

[bkatz]

I am going to be buying a 1968 Johnson 20hp outboard. I just looked at it, seemed to run fine and idled fine as well. The only thing I am worried about at this point is the compression. It was 120/115. Is this something that i should be worried about? Or is that normal? Just for some background, the engine has been used in fresh water, it has a rebuilt carb, new water pump, new points and all gaskets have been changed. Gear oil looks good as well. So what do you think...is it worth the investment and will at last?

 

[Howard Sterndrive]

Re: Compression Question...

The only thing I am worried about at this point is the compression. It was 120/115. Is this something that i should be worried about?

nah- that's pretty decent.
if it's been sitting a while, numbers might come up after a tank of fuel goes through it.
a decarb might also raise it...cleans the rings


good you checked the gear oil - lower units are getting a bit scarce for these and new lower gears and such are very dear.

 

[Mas]

Re: Compression Question...

Compression numbers are good. A good investment????depends on the amount invested. Will it last...yes...as long as you take care of it!


MAS

 

[jbjennings]

Re: Compression Question...

I agree, the motor sounds like a good one. But I've never met a boat that didn't like to pull money out of the owner. They're not good investments!
I think I know what you mean, though. The last thing you need to check is probably something you won't be able to check----will the clutch dog and gears HOLD gear at wide open throttle. You can't check that without running it. To me, the lower unit having no water in it is a good sign.
I wouldn't put much more than 3 or 4 hundred in it, myself.
Your compression numbers are fine. The standard I've been told is within 10% of each other, and yours easily falls within that range. Yes, it will last. Keep an eye on the water pump output, keep fresh gas in it mixed properly, and it will give you a lot of fun.
Nice motor!
JBJ

 

[bkatz]

Re: Compression Question...

Thanks for the input! As far as the gears go I had the motor in a test tank and it seemed to run great when wide open. The only issues I came across were the motor seemed to flood easily. But I took the plugs out got them as dry as I could and gave the cord a few pulls to get any gas out. I then started the motor without the fuel line attached and it started and ran for a good min. then I put the fuel line back on and had no other issues, this happened twice!

 

[Mas]

Re: Compression Question...

I do not know what you're asking, but running the motor without the fuel line just means that you're just using up the fuel that is remaining in the carb bowl.

Look toward a bad float needle and seat for a flooding issue.

MAS