I'm looking at a 2005 Ranger Z21 in another state with a Mercury 250 four stroke on it, sorry I don't have serial number yet, salesman is sending tomorrow. He says the hours on the motor are 230 hours. The compression are as follows:
#1 cylinder =170
#2 cylinder =190
#3 cylinder =175
#4 cylinder =190
#5 cylinder =190
#6 cylinder =185
Should this fluctuation in cylinder compression be something to worry about? I haven't never owned a for stroke so not for sure? Thanks
in cars i like to see less than 10% variation between cylinders. here that would be 19 psi from your highest 190 psi reading. your lowest is 170. so that's Very slightly over the 10%. Being that it's an outboard it may be slightly different acceptable range.
If it was me i wouldn't be too overly concerned, but there are 2 cylinders that's lower than the rest. #1 #3... Makes me wonder about them.
According to data in the Mercury Verado SM your motor appears to be just fine from a compression standpoint. Using Mercury's formula, and based on the highest cylinder in the motor you are looking at (190 psi), the lowest cylinder should be no less than 161.5 psi. The lowest cylinder you mention is 170.