Outboard compression test question

[Stratosman]

I want to see if I got this right. Pull all the plugs and using the compression guage, turn over the engine 4 or 5 times while reading the guage, take the highest number from each cylinder. Is this the correct way to perform a test. I assume the motor should be warmed up some prior to the test?

Any other advice would be greatly appreciated.

Thanks alot.

[Valv]

That's correct.

The way I do it, it's just remove all plugs, connect tester on a cylinder and crank it for few seconds. Take readings, and go to next cylinder.

I have to do this since I don't know if a motor is runninng or not or which condition it is prior to start it.

Correct procedure is to warm up engine, disconnect all plugs, put throttle at WOT (wide open) crank motor, and do readings.

I found out there's not much difference between my way and the "manual" way, the MOST important thing to remember is difference between cylinders cannot be more than 10%

Ifs a V6 has 4 cylinders at 125lbs, 1 at 105 and 1 at 65 it means it's "gone", even 5 at 125lbs and 1 at 65lbs is not good, but I had very few instances where rings were stuck on piston (due to long time inactivity), in this case a Ring Free soak overnight took care of the problem.

Also there's not much of a "standard" compression spec, I've seen motors with 185lbs and some with 85lbs, but below the 80's I would worry about it.

I think that's it, how about all of this after only 10 minutes you posted....isn't FishingMinnesota.com great or what ???

[Stratosman]

You're the greatest Valv. I kinda figured I'd get a response from you somewhere on this thread. You know how it is, you think you are pretty sure how to do something but you just want to make sure...

The one thing I would have forgot was the WOT upon testing.

Thanks again.

[Valv]

I wouldn't even bother with WOT, it will give you slightly higher results, my gauge barely picks it up.

Also to see if a ring is stuck or cylinder slightly scored, tilt motor mostly horizontal (if possible) the pour a spoonful of motor oil into plug hole and test compression again.

[Stratosman]

what does that do?

[Jeremy airjer W]

If the compression increases than there is a problem with the rings, piston, or cylinder wall. If the compression doesn't increase than the problem is higher up (unless the piston is in seriously ruff shape). Burnt valves or maybe a head gasket are a couple of possibilities

[Stratosman]

Okay,

I performed the comp. test as previously outlined. Warmed engine for approx. 20 minutes. pulled all plugs and tested individually. All cylinders tested as follows..

#1-4: 130 psi

#5: 125 psi

#6: 132 psi

This seems like it should be pretty good right?

Also, what would a leak-down test detect differently from a comp. test if anything and is this a better guage on a motors condition?

Thanks again all!

[Valv]

Sounds like a good runner to me.....

[musky hunter]

You've gotten some good advice on the engine. Luckily, you can rule out major engine damage or wear as a factor if it it still rough running as the compression test is near perfect. You are down to electrical or fuel deliver if you still think things are not running smoothly