compression amounts on 1993 40 hp johnson

[lundrebel]

I was wondering would be a good compression check on a rebuilt 40 johnson. What is the correct way of measuring? Thanks for any info

 

[SparkieBoat]

Re: compression amounts on 1993 40 hp johnson

run engine to operating temp..shut off..remove all the spark plugs, move the throttle to WOT position. connect compression gauge..turn over for about 4-7 secs or until you see the psi needle stop going up. you would want to see it around 120 +- 5 psi. but anything over 90 is ok as long as you do not have more than %10 difference.

 

[HighTrim]

Re: compression amounts on 1993 40 hp johnson

Very important to use a remote starter, or rig a simple jumper cable, to engage the starter solenoid without turning the ignition on.

On rope start engines, pull the emergency kill switch. I also ground out my plug leads to the block just in case.

Not really important to move the throttle to WOT, main thing is the the difference as stated, post your results.

 

[boobie]

Re: compression amounts on 1993 40 hp johnson

The OMC service manuals always stated no more than 15 psi difference between cyls, having mtr warmed up and throttle at wot position.