68 Johnson 55hp (TRL-10R) cold compression test low?

[DWM76]

Hi again all,

I decided to test cylinder compression now that I have the starter motor issue resolved. Pretty good chance I am doing it wrong since as mentioned in previous threads I am a total boat newbie and not a mechanic and I get my info from video's and the manual.
Results - cylinder 1 - 68psi, 2 - 70psi, 3- 72psi.
Method: Cold motor (have not confirmed it will start yet - waiting on replacement coil - bought without one) Guy said he had it running....sure.
Tested compression with spark plus in (2+ gauge in 3rd) I have since read to test with them all out?
Tested by charging starter directly - rebuilding wiring harness as it was too far gone with corrosion. Would this matter?
I have only residual lube in the lower unit gearbox as I previously rebuilt the water pump and shift solenoid assembly.

In order to get a more accurate compression reading what am I missing or doing completely wrong?

Thanks again!

 

[racerone]

Try with a " known to be accurate gauge "-----You should see 140 psi on that motor !!

 

[oldboat1]

screw-in style gauge, testing with all plugs removed. Crank until you see no additional increase (maybe three or four pulls with a recoil starter, a few seconds with an electric). It's a good idea to fill the l.u., and dip in a tub of water for testing -- don't want to spoil a new impeller. (Borrow or rent another tester.)

 

[boobie]

First thing you should do is see if you can get it started.

 

[DWM76]

Thanks for the advice. I filled the L/U with OMC premium lube and dropped it in water. Pulled the plugs and tested compression again with WOT. Slight improvement to 75-80psi. Top was lowest. Manual says 100psi minimum so not looking good.
When the coil gets here and I have the harness rebuilt i'll test again (assuming I get spark!)
With low psi, but variance between within 5psi can I assume the motor will function, just at reduced HP? I imagine likely harder to get started as well?

Thanks,

 

[racerone]

Throttle does NOT need to be wide open to do a compression test on that motor.

 

[DWM76]

I am curious if there is a difference WOT or not. The Manual says, "Insert a compression gauge into the No. 1 (top starboard bank) spark plug opening. Crank the engine with the starter, or pull on the starter cord, thru at least 4 complete strokes with the throttle at the wide-open position, or until the highest possible reading is observed on the gauge."
So WOT or not I should get the same result?

Thanks,

 

[racerone]

Correct.-----Intake and exhaust ports are WIDE OPEN when piston is at the bottom of the cylinder.-----Compression does not start till exhaust ports close.-----I am not sure who writes these manuals that you are using.