Compression test on a cold motor

[smsscuba]

I tested the cylinder compression on all three cylinders of my 1998 Johnson
35hp.I know that this should only be done once operating temp is achieved,but I am awaiting a replacement part and can`t start it just yet.

I got all three cylinders at about 105 PSI (cold).I tried it again numerous times and about the same results were achieved.

Is this a fair pressure reading for this age engine, taking into account that it is cold.

 

[oldcatamount]

Re: Compression test on a cold motor

It's fine. The key is that all three are close together like you have. Are you using a rope or electric starter? An electric starter will give you higher readings as it's turning the motor over faster than you would with a rope start.

 

[smsscuba]

Re: Compression test on a cold motor

It is manual (rope) start.

 

[DJ]

Re: Compression test on a cold motor

Fine.

 

[boobie]

Re: Compression test on a cold motor

If you want to keep that good compression you've got, remove the oiling system on it and use premix 50:1. Been there and done that.

 

[smsscuba]

Re: Compression test on a cold motor

How do I stop the oiling system without physically removing it from its location?

 

[Too Cycled]

Re: Compression test on a cold motor

Agreed.

Premix your fuel and your motor will work without mixture concerns.

I had a 1989 70 hp VHO Evinrude with oil injection ... one failed oil pump and $1400 later ... I now have a 1989 Johnson 70 hp that I premix fuel for.

From what I've heard, the design is flawed anyway as the fuel/ oil mix suffers during acceleration after a prolonged period of idle and does not remain constant at 50:1 as hoped.

I'm no pro ... more of an experienced victim of my own ignorance on the issue.

 

[boobie]

Re: Compression test on a cold motor

It's hard for me to explain on here but what you end up doing is remove the oil tank and oil pump as an assembly. Then you will have to do a little fuel line plumbing. What you end up doing is leaving the fuel pumps and fuel filter in the system going directly to the carbs by-passing the tank and oil pump. Don't forget to mix the fuel 50:1.

 

[v20 outrage]

Re: Compression test on a cold motor

You also must disconnect the wireing from the VRO or your alarm will drive you out of your mind.
You best change the fuel pump to a pre VRO age like 1985 as it has no oil system connected with it.
Sal

 

[boobie]

Re: Compression test on a cold motor

We are not talking about a mtr with a VRO. This mtr has an oil pump on it that is simular to the old Accumix that OMC built in 1987 and was not worth a S#%t. When you remove the oil tank the pump and electronics come with it. This was one good mtr and if the owner wants to keep on using the oiling system on it all I can say is Good Luck. Seen too many of them blow. I'm done preaching !

 

[posuelo]

Re: Compression test on a cold motor

hi i'm going to buy a 2001 150 hp johnson ocean pro ,is a 110 psi a good piston compression?

 

[posuelo]

Re: Compression test on a cold motor

there is any one to helpme on this question please?

 

[boobie]

Re: Compression test on a cold motor

You may want to start your own thread. You will get better replies.