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  1. #1
    otoss's Avatar
    Join Date
    Mar 2010

    question on compression test

    Hi all,

    Can't post on the how section so I'm posting here. How do you do a compression test on the cylinders?

    If someone as a link that explains how to do it please post it. I never did a test and wouldlike to do it.

  2. #2
    I pew pew lazors
    Join Date
    Mar 2010
    1. Buy a compression gauge and a 5/8" deep plug socket. i believe you need something with 12mm threads for the gauge (someone will correct me if wrong). If you don't have an 18" extension for your ratchet, pick one of those up too.

    2. Remove the oil dipstick from the dipstick tube and pull the plastic cover off the top of the engine to expose the coils. Reinsert the oil dipstick.

    3. Disconnect the coil and pull it off the spark plug. A little twisting might be required if the coil won't give but don't beat them up too much.

    4. Remove the spark plug from the engine.

    5. Thread your compression gauge into the spark plug hole. Be extremely careful to not cross thread. I repeat, BE CAREFUL to not cross the threads. Only tighten finger tight.

    6. Hold the throttle WOT and crank the engine. I usually count 10 "cranks" per piston (just to stay consistent).

    7. Record the reading.

    8. Remove the compression gauge. Most have a button to "depressurize" the gauge.

    9. Add anti-seize lubricant to the spark plug threads and reinsert the spark plug. Again, BE CAREFUL not to cross the threads. Tighten finger tight. Then tighten with the ratchet an additional "one 1/4 turn". I think the exact torque spec is something like 18 inch pounds (someone can correct me on this again too).

    10. Reinsert the spark plug coil. Add some marine grade grease around the top of the spark plug boot (near the lip). This will help keep water out. Make sure the coil fits snugly on the spark plug.

    11. Don't forget to plug the coil back in.

    Do this for all three cylinders. And DO NOT cross the threads!

    I hope this helps.

  3. #3

    Join Date
    May 2007
    Miami FL
    Thanks Peebee. I know is old but i am new to 4tec engines and wanted to make sure i didn’t need to ground anything.

    Can someone tell me what the compression is for a Non Supercharged 2004 sportster.

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