How To: Compression Test

[Red Devil]

Can someone provide a detailed "how to" compression test? For instance, are all 3 plugs supposed to be out and should the throttle be held wide open while cranking? I remember Miketrin did a nice one for me with the spark plugs last summer.

[Jeff C]

Devil:

Get the ski warmed up....... Take out a plug at a time, screw in the tester, zero it out, hold the throttle WFO and crank it for about 5 seconds or so.

Look at the reading. Move on to the next cylinder, lather/rinse/repeat......


cylinders should be within 5-10 psi of each other. Some people say within 10%

[boataddict]

Do not waste your money on a cheap tester. I have a Snap On but I am sure that there are less expensive ones out there.

[Red Devil]

Thanks guys....

[RXP-REX]

What numbers should we be looking for when checking compression on the 4-tec SCIC engine? Like what should each cylinder's compression be?

Thanks.

[RX951]

http://www.greenhulk.net/forums/show...ession+testing

[RXP-REX]

http://www.greenhulk.net/forums/show...ession+testing

Thanks RX951. One more quick question though. Your "How To" is in the Yami section. Do the 150psi readings account for us RXP guys too? I didn't think we ran the same compression as you GPR guys?

[RX951]

Thanks RX951. One more quick question though. Your "How To" is in the Yami section. Do the 150psi readings account for us RXP guys too? I didn't think we ran the same compression as you GPR guys?

No, I'm sure compression is different due to different motors, but the process of obtaining the compression readings correlate. One plug at a time.

[RXP-REX]

No, I'm sure compression is different due to different motors, but the process of obtaining the compression readings correlate. One plug at a time.

Right, but I was wondering if anyone knew what the compression should be for each cylinder on an RXP engine?

[friebe1]

145-155 would be normal. The key is to test on a motor after it has run and reached operating temps and has a fully charged battery.
I like to use the within 10% rule so as long as they are all within 15 psi of each other, no worries.
If they are not, then do a leakdown test to see where the leak is.
Steve