Advice on '79 6 HP motor

[weekendfisher]

Hi Guys,
Just picked up a clean '79 model 6 HP Johnson two cylinder as an auxiliary for my half cab.
I have a few questions about it as i have not have much experience with the smaller HP motors.
What i wanted to know is what sort of compression should i expect on each cylinder ?
Also how hot should the water coming from the tell tale be ? It does seem to come out alot warmer than from larger motors.
I can't see any issues with it and it starts first pull of the cord so i believe its ok just wanted to know a bit about it.
I bought it from a marine mechanic so i trust it is in good working order.
Thanks

 

[outboards115]

Re: Advice on '79 6 HP motor

Hi,
I think the compression for these motors should be between 75 and 120 psi, also if the compression is below 60 psi you might want to get it cheked out. I think you should check out the thermostat and replace the water pump if the water is comeing out hot.

 

[Bosunsmate]

Re: Advice on '79 6 HP motor

My rule of thumb is so long as you can put your hand on the head for a while its not too hot. The thermostat if your engine has one open around 65degree celcius. So long as its not near the temp of a cup of tea it should be within limits
Ive had a look at one model 79 6hp and i couldnt see a thermostat, so long as a good steady stream of water is coming out the telltale its very unlikely to be malfunctioning.Just check when your using it at high throttle that the telltale is working otherwise it might be pressuring (exhaust gases into the water jacket, but im sure thats not the case with yours.
You want your compression readings to be close to each other with the plugs out.i dont know what the readings are expected for that motor

 

[weekendfisher]

Re: Advice on '79 6 HP motor

Thanks guys,
The motor gets warm but i can hold my hand on the head the stream of water would be about 30-35 degrees Celsius so i guess that sounds ok
The compression was good 91PSI on the top cylinder and 88PSI on the bottom cylinder so not to bad for a 33 year old motor.
I am curious as to how the insides look as the head looks like it has never been removed the paint on the bolts is still intact.
Th head looks good no signs of leaks or warping but if the head has never been removed i might pull it off and replace the head gasket as a precaution
Thanks for all of the help guys

 

[Bosunsmate]

Re: Advice on '79 6 HP motor

Careful with the head bolts as if some have seized over time it may turn into a long job. They a smaller and more fragile than the ones on the bigger motors you'd be familiar with