How to do a Compression test

[TrickStang37]

title says it all. Ive ripped apart the motor couple times, even my friends motor, bu tI never done a compression test before, i know its easy. in my chiltons book it says to turn the motor over with the "auxiliary start switch", what and where is that?? i thought you turn it over with the ignition switch but it says to leave it in in the OFF position.

 

[HISSIN50]

short version. warm motor up. disconnect the ignition and crack the TB wide open. pull all plugs. then do the test (dry). then do the wet test (tiny amount of oil in each cylinder - be aware of hydrolock). absolute numbers dont mean as much as relative numbers, IMHO.

when you buy a compression tester, it should have some detailed instructions.
good luck.

 

[Michael Yount]

The compression gauge should have a fitting that allows you to screw it into the spark plug hole - remove the plug of course. Unplug the coil wire so the engine doesn't start - then while holding the throttle wide open, turn the motor over for a few seconds. The better gauges have a check valve that will hold the reading for you. In the old days you needed to be able to look at the vacuum/compression gauge while you were cranking. Back in the day, many cars had a button under the hood that allowed you to engage the starter without the ignition switch being on - for maintenance/repair reasons.

Work your way around all 8 cylinders. Readings should be within 5-10% of each other. The actual number will vary depending on how the engine is cammed, what the static compression ratio is, etc. It's good for identifying a particular cylinder that's having some sort of problem. A leak-down test is better for determining how well cylinders are actually sealing.

 

[Daggar]

The auxiliary switch is a tool you can purchase from an autparts store that basically "shorts" the terminals on the start solenoid so that the motor turns over. You can so the same thing with a metal wrench or a screwdriver.

Reference: Gone in 60 seconds where sex goddess Angelina Jolie was jackin Ferraris from the storage facility. hehe

 

[Michael Yount]

Angelina Jolie - I'm sure she'd appreciate we spelled it right.

 

[Daggar]

My bad... correction made. Sorry honey (if you're reading this)... Tuesday night still good with you??

 

[HISSIN50]

Back in the day, many cars had a button under the hood that allowed you to engage the starter without the ignition switch being on - for maintenance/repair reasons.

i guess stangs are old - one can remove the slide-on terminal on the solenoid and touch it to the hot (battery) lug on the solenoid. the car will crank, but if the key is off, it should not start (unless one has done a diesel transplant).

 

[Michael Yount]

She can't take your message right now....what's that honey? Yeah, I'll be right back in there. Gotta go guys.

 

[HISSIN50]

She can't take your message right now....what's that honey? Yeah, I'll be right back in there. Gotta go guys.

ok, this is just getting weird.

um, Michael, I'm thinking that Vegas agreed with ya after all. J/K.

 

[Michael Yount]

Sorry - I don't usually get caught up in that stuff. Happily married for 31 years; but something about her mouth.....oops, yeah, this IS getting weird.

And we all know what happens in Vegas, stays in Vegas.

 

[HISSIN50]

Sorry - I don't usually get caught up in that stuff. Happily married for 31 years; but something about her mouth.....oops, yeah, this IS getting weird.

And we all know what happens in Vegas, stays in Vegas.

Michael, you are in rare form tonight. Keep it coming (i know i let that one go).

the stuff between you, Daggar and a certain someone is quite amusing.

 

[bln92cpe]

Sorry - I don't usually get caught up in that stuff. Happily married for 31 years; but something about her mouth.....oops, yeah, this IS getting weird.

And we all know what happens in Vegas, stays in Vegas.

Damn...I didnt know old timers were on the s site LOL

 

[Michael Yount]

JT - go back to the 230F degree post - now he's after you too....

 

[HISSIN50]

JT - go back to the 230F degree post - now he's after you too....

just addressed him as politely as i could. no one on here has called me a freak before.

i almost choked while reading some of his posts. he knows things about you and what you like to do in your spare time that i bet you did not even know. I'm enjoying it and eagerly awaiting the next round of witty repartee (you and Dags are doing quite a nice job, BTW).

 

[HISSIN50]

Damn...I didnt know old timers were on the s site LOL

always good to come in here and disrespect the most knowledgable person in here (Guru).
BTW, i have respect for my elders. i hope to learn 1/10th as much as he has forgotten.

 

[83GT289]

interesting thread.. especially the Angelina comments. Mmmmmmmmm.

 

[Daggar]

She can't take your message right now....what's that honey? Yeah, I'll be right back in there. Gotta go guys.

Dammit! Ahh well... I suppose if I didn't mind Billy Bob, I can get over whatever followed. Just clean her up b4 tuesday huh?

 

[Michael Yount]

"Spit" polished. Can't believe I said that.

bln92cpe - yup, there's some oldtimers aboard. I'll pass along a tip. You can tell the old timers 'cause they know how to spell.