CHECKING COMPRESSION WITHOUT RUNNING MOTOR???

FISHNFLI

Recruit
Joined
Jan 29, 2002
Messages
4
I AM LOOKING AT A 79 85HP V4 JOHNSON TO PURCHASE AND I WOULD LIKE TO CHECK COMPRESSION BEFORE I PURCHSE IT. MOTOR HAS NOT RUN SINCE 92, WAS FOGGED, BUT I WILL NOT BE ABLE TO START IT TO TEST COMPRESSION. I HAVE CHECKED COMPRESSION MANY TIMES ON AIRCRAFT ENGINES BY SCREWING IN GAUGE AND HAND TURNING THE PROPELLER. CAN I PUT THE JOHNSON BOAT ENGINE IN GEAR AND HAND CRANK THE PROP TO GET A COMPRESSION READING??? OR TURN PROP NUT WITH WRENCH UNTIL I GET TO CYLINDER UNDER TEST??
 

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: CHECKING COMPRESSION WITHOUT RUNNING MOTOR???

Howdy FnF,<br />I think I would turn engine over with ah big ole sock wrench on the flywheel nut. Be sure ignition system is grounded. <br /><br />c/6<br /><br />hooty
 

hondon

Lieutenant Commander
Joined
Jun 11, 2001
Messages
1,922
Re: CHECKING COMPRESSION WITHOUT RUNNING MOTOR???

You can always use a rope with a knot on the end to turn the motor over .You will find the flywheel notched for exactly this purpose.Not sure how much I'dd rely on compression readings doing it that way though as you wo'nt get much of a spin and you'll probably be pretty worn out and p.oed by #3.Why can't you crank her over?
 

petryshyn

Commander
Joined
Oct 3, 2001
Messages
2,851
Re: CHECKING COMPRESSION WITHOUT RUNNING MOTOR???

Hi Fishnfli<br /><br />You don't have to run it to check compression, although it is better if warmed up. Just bring along a battery and booster cables, and crank it over. I'd want to lube the water pump with water or RV anti-freeze (pending on outside temp.) before you crank. If circumstances dictate that you cannot check compression, assume its bad....<br /><br />just my .01 worth.... :)
 
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