30 PSI Compression both cylinders 1979 evinrude 35hp 2 stroke

Squatch0817

Cadet
Joined
May 19, 2020
Messages
22
I have 30 psi in both cylinders of my 1979 evinrude 35hp 2 stroke engine. its only electric start. the starter is seized up but the new one should be arriving in a a couple weeks. i got the reading of 30 psi in both cylinders with a rope pull on the flywheel. is the rope pull adequate enough for a compression test or do i need the electric starter to perform a proper compression test?
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,793
You can use a Rope to test compression, you will likely have to do it several times, until the gauge reads no higher. That engine isn't too big about 32 Cubic inches. If both cylinders are low, it could be a bad Head Gasket.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
I think there is more to this story than you are telling us.. Seized starter? No compression? OK, so was it submerged or what? Or overheated and fried?

Anyhow, to continue with the guessing game, if you suspect a blown head gasket, remove the cylinder head and look.

Too bad you already sprung for a new starter.
 

Squatch0817

Cadet
Joined
May 19, 2020
Messages
22
I do t know much about the motors history. Just bought the motor. I know that the cowling was off for some time and was in the rain.The motor is not seized at all. 30psi in both cylinders. Not trying to keep info from y’all. Just don’t know much about the motor.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
I believe jimmbo was suspecting you were only pulling the rope one time. If that is correct, then do it with multiple pulls before tearing into the head gasket.
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,605
And make sure you remove the spark plugs on all cylinders when doing the compression test. It pulls way easier and will still give you the numbers. As for the starter, could have been an easy disassembly and cleaning to get it working again. JMHO
 

Squatch0817

Cadet
Joined
May 19, 2020
Messages
22
I’ve pulled the rope about five times and only get 30 psi in both cylinders. I’m not sure what to do from here as for the starter goes I took it apart and it was all corroded and seized up inside.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,793
What do you mean by Seized Up? That term is usually used when you can't get the crankshaft to turn.

Those engines are quite common, probably cheaper to find another, than to rebuild this one.
 

Squatch0817

Cadet
Joined
May 19, 2020
Messages
22
The starter was seized up not the engine itself. I just don’t have a good compression on either cylinder of the engine. What can cause that? About 30 psi compression in each cylinder.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,744
With 30 PSI compression just pull the cylinder head off.----Not the water jacket cover.--10 bolts or so and you will have your answer.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,793
On the Cylinder Head there is a Water jacket cover, it is held on by a number of small Bolts/Screws. The Clyinder Head Bolts are Larger,
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
13,793
Don't take the Cover off, just remove the Cylinder head
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
I’ve pulled the rope about five times and only get 30 psi in both cylinders. I’m not sure what to do from here as for the starter goes I took it apart and it was all corroded and seized up inside.

See, that is why I suspected the motor had been submerged. Yes, rainwater could have gotten in, but that much?? Anyhow, you are now to the point of investigating the possibility of a blown head gasket. If it is blown, it will be obvious when you get the head off. You will also be able to see stuff like battered up parts or other physical damage.

If, IF, you truly only have 30 psi (gauge reading correct) and you don't find a blown gasket, then the motor is going to need some more disassembly to find the compression problem. Who knows?? Submersion, ran hot, ran without oil, who knows?
 

Squatch0817

Cadet
Joined
May 19, 2020
Messages
22
See, that is why I suspected the motor had been submerged. Yes, rainwater could have gotten in, but that much?? Anyhow, you are now to the point of investigating the possibility of a blown head gasket. If it is blown, it will be obvious when you get the head off. You will also be able to see stuff like battered up parts or other physical damage.

If, IF, you truly only have 30 psi (gauge reading correct) and you don't find a blown gasket, then the motor is going to need some more disassembly to find the compression problem. Who knows?? Submersion, ran hot, ran without oil, who knows?

Thank you for the info the head gasket was defintiely blown so was the water case seal and the thermostat. i may change the rest of the gaskets but i haven't investigated the other gaskets too much yet. what do you think about changing out the rest of the gaskets? the pistons and cylinders look pretty darn good.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
And we are back to the same question. WHY is the head gasket blown? They don't do that without a cause. Most often cause is overheating. If it was overheated, all of the gaskets related to exhaust heat need to be replaced also. Not a simple job. But once you get the exhaust covers off, you will be able to see the pistons' sides and look for heat damage. Be prepared for the worst. If the worst doesn't happen, well this is your lucky day.
 
Top