Compression test gone bad

[uofm rebel]

I decided to do the right thing and perform a compression test on a '98 25hp Johnson before purchasing it; however it seems that this was my first mistake. I read every post on compression checks before performing my first and none mentioned this particular issue. The piston hit the last thread of the compression gauge adapter which boogered the threads as well as knocking a a small ding in the top of the piston. When I unscrewed the gauge, with the help of a socket, the warped threads did very little damage to the threads on the head. ie. I am able to screw the spark plug in by hand so I do not think I will have to tap the hole. My concern is for the piston. I've had differing opinions from mechanics that I have talked w/on the phone. One tells me to run it and not worry about a small ding and another tells me; Heli coil$25, head gasket $25, labor $150 to inspect. I have not ran the motor since purchasing as I am afraid of what might happen. Motor ran fine on the test and the compression of that cylinder was 120. Did not test other cylinder due to first cylinder stupidity. Any suggestions? Any clue as to cost of new piston? <br />"If it wasn't for bad luck I'd have no luck at all."

 

[ob]

Re: Compression test gone bad

uofm rebel,If the compression after your mishap produced 120 in that cylinder it may be just fine.On the other hand ,depending on the depth of the ding in the piston dome,it could potentially lead to a hot spot or fracture under load.So the million dollar question is,can you rotate piston to TDC and with the plug removed give us some indication as to the severity of the ding and we can better advise.Don't know what type of adapter you used to run compression test,but you alaways need to insure mechanical clearance with a hand rotation before cranking.That's a mute point now. Post back and tell us what you find.