Compression Test??

[MASTER Brian]

When doing a compression test on a 1977 70hp Evinrude, do I need to ground out the plugs? ....or can I just leave them hanging? If I need to ground them what is the best way to do this?

Also, besides 10% of each other, any idea of what factory compression is?

Thanks

 

[Daviet]

Re: Compression Test??

Yes, ground the plug wires. Use jumper wires or anything that will ground them, I have a 4 point spark checker that I use.
I have never found any listed compression standards, probably anything over 100 to 110 would be good.

 

[Challenger84]

Re: Compression Test??

to give you an idea.. my 70hp johnny has 150 psi on all 3 cylinders.

 

[MASTER Brian]

Re: Compression Test??

Thanks for the replies. I have a Clymer manual that covers this motor and it says to disconnect the power pack to armature place connector to disable the ignition system.

Is that actually necessary and doesn't removing and grounding the plugs essecentually do the same thing? Or is this their way around grounding the plugs?

The book just says "should not be less than 100psi."

 

[Challenger84]

Re: Compression Test??

Their shouldn't be more then 10% differencebetween them and under 100psi.
I think 100 psi is the bear min.

 

[Narojobra]

Re: Compression Test??

Is this why I don't have spark anymore? I just unplugged all 3 plugwires, removed the plugs and conducted the test. Now I have no spark. Did I just blow my power pack?

 

[MASTER Brian]

Re: Compression Test??

Is this why I don't have spark anymore? I just unplugged all 3 plugwires, removed the plugs and conducted the test. Now I have no spark. Did I just blow my power pack?

There is a good chance, but someone should be able to test it.

 

[JB]

Re: Compression Test??

Do not get hung up on psi. It can differ greatly depending on the guage, conditions and technique.

If all cylinders fall within 10-15% the engine is healthy.

Look in the Top Secret File for detailed instructions on one way to do a safe compression test. Leaving the ignition on killed it.

 

[MASTER Brian]

Re: Compression Test??

Do not get hung up on psi. It can differ greatly depending on the guage, conditions and technique.

If all cylinders fall within 10-15% the engine is healthy.

not really too worried, about psi at this point.

Look in the Top Secret File for detailed instructions on one way to do a safe compression test.

I looked there and guess I'm confused about this statement. "The starting jumper (step #4) goes from the +12V cable to the terminal that the starter switch normally puts +12V on to start." Are you saying to basically run a wire from the +12v on the battery to the +12v connection on the starter and that this will crank the engine bypassing the electrics?

Leaving the ignition on killed it.

Wasn't me that killed the ignition, another poster.

Sorry about the sort of double post, but the thread has started to become more about psi and a possible killed ignition. Something I'm trying to avoid............