Jump to content
  • GUESTS

    If you want access to members only forums on HSO, you will gain access only when you Sign-in or Sign-Up .

    This box will disappear once you are signed in as a member. ?

  • 0

How to check compression on motors


Valv

Question

You can check compression yourself or have a shop do it for you.

It's a very simple procedure, go to Walmart (or any auto part store) buy a compression tester for $ 30.00 (automotive section), take all plugs out, thread tester in and crank motor keeping WOT (Wide Open Throttle), repeat process for every cylinder and record the results, you don't want anything more than 10% difference in between. The compression can vary from motor to motor, you can see from 85lbs to 175lbs depending on motor and year, but below 85 it's very suspicious. Now, if you find a cylinder that is almost flat, try to pour a little of motor oil in the hole, then test again, if it reads much more than previously (almost like the others) you MIGHT have stuck ring(s), caused by carbon, they will loosen up when you start motor.

This is normal, but very uncommon, 95% of the cases you have a bad cylinder...walk away regardless of how good is the deal (unless it's free) or how good loooking is the rig.

Link to comment
Share on other sites

1 answer to this question

Recommended Posts

  • 0

Three things

1. Make sure to disable the fuel and/or ignition systems.

2. Be consistant. Usually a motor will make a distinct sound once every revolution. I usually give each cylinder at least three revolutions to show me what it has.

3. If you have two cylinders right next to each other with low compression and the oil trick doesn't work, theres a good chance the head gasket has failed between the two cylinders.

Link to comment
Share on other sites

Guest
This topic is now closed to further replies.


×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use and Privacy Policy. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.