Guests - If You want access to member only forums on FM. You will gain access only when you Sign-in or Sign-Up on Fishing Minnesota.

It's easy - LOOK UPPER right menu.

Sign in to follow this  
Followers 0

How to check compression on motors

2 posts in this topic

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.

Share this post

Link to post
Share on other sites

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.

Share this post

Link to post
Share on other sites
This topic is now closed to further replies.
Sign in to follow this  
Followers 0

  • Posts

    • eyeguy 54
      loaves of bread........   where did you go to school??    and how would you shave??   
    • DonBo
      Leftover spring turkey permits go on sale March 20 The 105,464 leftover permits for the 2017 spring turkey hunting season will be sold on a first-come, first-served basis beginning Monday, March 20 at 10 a.m. Leftover permits will be first issued for sale by zone, one zone per day. The following zones have leftover permits, and scheduled sales dates are as follows: Zone 1 - Monday, March 20; Zone 2 - Tuesday, March 21; Zone 3 - Wednesday, March 22; Zone 4 - Thursday, March 23; and Zones 5, 6 and 7 - Friday, March 24 (due to the low number of permits left in these units, sales have been combined into one day). After zone-specific sales, all remaining turkey tags will be made available for purchase Saturday, March 25. Extra turkey tags can be purchased at a rate of one per day until the zone and time period sells out or the season closes. Leftover turkey permits cost $10 for residents and $15 for non-residents – each will have equal opportunity to purchase over-the-counter permits. All hunters are required to purchase a spring turkey license and 2017 Wild Turkey Stamp, unless they have previously purchased the license and stamp or are a 2017 Conservation Patron License holder. Leftover permit purchases will not affect preference point status for future spring or fall turkey permit drawings. Leftover permits can be purchased online through   and at all license agents. Hunters with any questions regarding permits should contact the DNR Customer Call Center, open 7 a.m. through 10 p.m., seven days a week, at 1-888-WDNRINFo (1-888-936-7463).
    • Borch
      Raining hard up there too JI'm?  Been raining here all day with a couple thunderstorms rolling through to boot.  Hope to still find some good ice up north before it's over.
    • Cliff Wagenbach
      No I have not. Cliff
    • leech~~
        Yep, it maybe a good weekend for all of us to head up to Jim's area this coming weekend! Let's do another GTG!