Simple compression test question!!!!

[couger300]

Hell all, I'am looking at purchasing an older 1 owner Celebrity 200cc that is in absolute incredible condition. The engine is a 5.7/260 engine with alpha one drive. I will be going to take it for a water test this weekend and I am going to request that I be able to do a compresion test following the drive. I've only owned and done repairs on 2 stroke outboards. I have 2 quick questions. What wire needs to be grounded and how do I recognize it. Roughly what readings should I expect to see? This forum has been very helpful in the past so I figured I'd just start with the experts! Thanks in advance!

 

[Fishermark]

Re: Simple compression test question!!!!

You basically want to make sure the distributor is not firing. What needs to be grounded is going to be different with different ignition systems. You can remove the main cable and be done with it.

Be sure to remove all spark plugs and have the throttle wide open. Then turn the engine over through at least four full revolutions - watching the gauge with each turn of the engine.

 

[Bt Doctur]

Re: Simple compression test question!!!!

using a jumper remove the coil wire from the cap and ground it or
unplug the ign module from the port riser or
remove the purple wire from the + side of the coil
remove all the spark plugs
Then with the throttle wide open crank for 3-5 revolutiuons and record reading.
with unknown year, service history, number of hours between 100 and 175 psi, hi to low within 10%

 

[81 Checkmate]

Re: Simple compression test question!!!!

Unplug the single coil wire from the top of the coil and ground it...Then do as Fishermark said......Look for a Consistent number reading between all cylinders.......If they are in the 90 psi range but consistent it means you still have compression but it's getting tired. 140 to 150 psi range is good healty motor.