compression

[scatgo]

Anyone have a clue as to what the compression should be on a Johnson 1980 35hp two cycle two cylinder shold be? The Selco online manual seems to go on forever about the difference between the two cylinders should be this or that but I have yet to find out what the psi should be.

 

[racerone]

Is it a SELOC manual ?------Post your values.------I would be looking for about 120 PSI .------Very few books post the factory values as there are many variables on testing.

 

[boobie]

Does this motor have a rewind starter ??

 

[scatgo]

Going to do the compression test this weekend if the weather holds out. It was a pull start. It was switched out to electric. start. Just noticed a hose that connects to the intake manifold and runs up to the upper cylinder head. Anyone know the reason for this hose?

 

[racerone]

Do not know what you mean by " upper cylinder head "-----Post a few pictures of this hose.

 

[scatgo]

Part number 92 in the diagram. Connects to bypass cover just under the top cylinder.

 

[racerone]

That hose goes to the bypass cover and not an " upper cylinder head "------It just gets rid of any extra fuel in the intake manifold.

 

[F_R]

I think he means #92 going to the upper bypass cover, not cylinder head.

 

[scatgo]

Ment to say below cylinder head. Sorry about that. Thanks for the help people.

 

[Bosunsmate]

Hard to know precisely unless your compression tester is recently calibrated. I had this motor it had about 118 on bottom 103 on top and went well for life. Sold it years later for more than i paid. Salty too

 

[scatgo]

Should the test be done with engine warmed up both sparks removed and WOT?

 

[boobie]

Yes !.............

 

[oldboat1]

I'll vote for both plugs removed, just to get a better/faster crank. Additionally, you don't want the second cylinder to fire while testing the first! (At least pull off the boot.) Keep pulling it over or cranking with the starter until the needle stops moving.

Warm might give you a little higher reading. Throttle position should make no difference on a 2-cycle motor -- do it if you better trust the results that way.

 

[scatgo]

OK looks like iam getting 80/85.

 

[racerone]

Your gauge is junk.-----Or there is something wrong with the motor.----Cheapest inspection is to remove bypass cover to look at pistons & rings.

 

[scatgo]

Did test my new compression tester after getting those numbers.

 

[racerone]

So is your gauge reading properly , yes , no or do not know ?

 

[scatgo]

Tested good.

 

[racerone]

Head gasket may be blown.--------Head gasket is cheap compared to jumping up and down and guessing about your motor.

 

[oldboat1]

If replacing the head gasket (should do that), resurface the head -- and while you are in there, good to clean out the water passages with a flat blade.