Small Engines (Lawn Mowers, etc.): Compression, compression check, plug hole

Question
HI Mike

I wrote to you the first time on the 16th of May about my Murray 6HP self propelled not cranking because I either hit something, not enough oil, or the grass was to thick and choked out. I tried to restart it but noticed it wasn't as firm when I pulled the rope as before. I got the flywheel of and the pin looks good. Next im going to borrow a compression gauage and see how this looks. I have a few questions about this. I have not replaced the pin and the flywheel yet. Will I need to do this before I check the compression? How many cranks will I need to pull? What pressure am I looking for? I just want to make sure I get a true and accurate reading.

Also before I do any of this someone told me to spin the blade as Im looking in the spark plug hole to make sure I see movement going on in there. I guess I should see the piston bobbing up and down as it goes thru the strokes? If that looks good then its on to the compression check?


Thanks for your help!

Steve

Answer
Hi Steve,

You can check compression without the flywhel installed.  Pull it over a few times, looking for at least 75 psi. 150 would be better.
Yes the piston should move as you turn over the engine.
Low oil??  If that was the case, engine damage may have occured.

Keep me posted,
Michael