about to do a compression test

Thread in 'Technical Questions' started by BillyBoy722, Jan 16, 2011.

  1. BillyBoy722

    BillyBoy722 Member

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    hi,

    i went to halfords and bought a compression test and ive read the instructions and understand what to do just wondering if anyone else has any more tips for me apart from what it says on the piece of card.

    if anyone wants to know which one i got this is the link to it!

    Halfords | Gunson Hi-Gauge Compression Tester
     
  2. McLarenboy

    McLarenboy Member

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    it's just that easy
    - drive the car to get the engine hot
    - remove fuelpump fuse
    - remove sparkplugs one by one and check compression
     
  3. BillyBoy722

    BillyBoy722 Member

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    sweet easy peasy then!

    what is the usual compression for a not fooked cylinder etc etc
     
  4. dazl71

    dazl71 Member

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    Warm it up. Unplug CAS and remove all the plugs, expell hot air via cranking for a second or 2 then install tester as per destructions hold on WOT and crank away until a peak reading is seen, record and repeat on others
    Thats about it mate.

    Everyone has there way to a point as long as it gets the job done ;-)
     
  5. McLarenboy

    McLarenboy Member

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    good compression result for the CA18 is >10 bar.
     
  6. BillyBoy722

    BillyBoy722 Member

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    has anyone got a pic of the CAS plug that i need to unplug??
     
  7. Stavros

    Stavros Active Member

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    The thing on ther front of the cam cover mate, easy peasy.

    As long as you got 'some' compression, and they all within about 1bar of each other, dont worry, the car is ok.
     
  8. BillyBoy722

    BillyBoy722 Member

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    okay cool thanks alot!
     
  9. tathan

    tathan Member

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    it's the big thing on the end of a cam.

    reading isn't massively important, any number around 10bar is ok, but it's more important that they're all the same.


    edit: damnit, must learn to type faster
     
  10. diamondsink

    diamondsink Kyouto Drift

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    You need to have a good battery. A sr should be around 150psi. You need to crank it till it stops rising. Get a mate to watch the gauge.
     
  11. BillyBoy722

    BillyBoy722 Member

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    not got a mate mate. Will just use the wife instead ftw lol battery is shizer but got a booster to get it going to do the test on the car. Cheers for tips
     
  12. milez

    milez Active Member

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    How did you get on?
     
  13. BillyBoy722

    BillyBoy722 Member

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    not done it yet. Plan on doing it on tuesday if the wife can help if we aint had our baby yet. Would do it tomoz but got a range so going to be out all day.
     
  14. Mitch

    Mitch In moderation

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    PM sent with step by step instructions. Leave your missus indoors to be pregnant, you can do it yourself.
     
  15. BillyBoy722

    BillyBoy722 Member

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    cheers for the step by step Mitch but sadly couldnt do it this morning as went hosp and then when tried it discovered that the battery is flat as a pancake! so gutted tried a few things to sort it but didnt work so going to get a trickle charger and charge the batt for a while and see if that sorts the batt otherwise just going to have to get a new battery!
     
  16. GrimR33per

    GrimR33per Member

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    Heres a guide i did.. May help abit ..

    [ame=http://www.skylineowners.com/forum/showthread.php?t=158553]Skyline Owners Forum[/ame]
     
  17. r3k1355

    r3k1355 Well-Known Member

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    Not alot of help unless you're logged into the Skyline OC.

    Copy and paste it here?
     
  18. BillyBoy722

    BillyBoy722 Member

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    Copied of Skyline Owners

    It will tell you if your engine has good compression. An engine is essentially a self-powered air pump, so it needs good compression to run efficiently, cleanly and to start easily.

    As a rule, most engines should have 140 to 160 lbs. of cranking compression with no more than 10% difference between any of the cylinders.


    CLICK HERE FOR RB ENGINE COMPRESSION PRESSURE REFERENCES



    Strong compression is essential for an engine to run properly and efficiently. A noticeable loss of power or efficiency, or blue white smoke may be cause to test an engine's compression. .

    A compression test measures how much air an engine's pistons are compressing, which can be compared against one another, and against manufacturer standards to determine if there is a problem in this area. While a lack of compression is most common, it is also possible for compression to be too strong. Over-compression can result in a problem known as detonation, which can be very damaging to an engine's internal parts.


    Low compression in one cylinder usually indicates a bad exhaust valve. Low compression in two adjacent cylinders typically means you have a bad head gasket. Low compression in all cylinders would tell you the rings and cylinders are worn and the engine needs to be overhauled.





    All you need to test your engine is;


    A compression testing kit. Range from £20 - £25 from any Motorstore

    1/2'' inch Ratchet

    A Spark Plug socket, (helps if it has a rubber grommet inside) with extension bar

    And in my case (CA18Det) Might be the same for RB, cant remember. Anyone confirm?

    A 3/8" inch Ratchet (5/16mm bit) with extension bar

    Or a Possy Screwdriver. However, the ratchet and socket will work better than the screwdriver as theres a chance you will grind down your screws!!

    And a wire brush if you wish to brush down your sparkplug tips.

    Also make sure your battery is healthy and full of charge..

    [​IMG]

    In the packet there are 2 Sparkplug sizes. The main is the one you will need.

    [​IMG]

    Start your car and leave it running for 5 minutes. Dont leave it to long or it will be to hot to attempt to do this..

    Turn off ignition..

    Now to start getting your hands dirty. Remove your coilpack cover. These bolts are normally 10mm.... Keep them safe and dont drop any in your engine bay. You may never see them again, Lol..

    [​IMG]

    You will now see your coilpacks...

    [​IMG]

    So the next step is to remove these. There are 2 ways of doing this.. One is to remove all bolts and remove all coilpack individually. Im doing it the quicker way and removing them all on the plate they sit on.

    The quicker way is that there are 2 different size (in length bolts). Some bolt to the head, and others to a plate that hold the coilpacks. There are usually 4 on each coilpack. 2 of which are different colors on each coillpack.

    In the CA's case, the Black bolts are the ones that need to be loosened, or removed. Leave the gold ones.. You can use a screwdriver but try not to ruin the head of the bolt. It is advised to use the right socket for it. Be much easier. 5/16mm in this engines case

    [​IMG]

    Once done lift them up and move them out the way....

    [​IMG]

    Now you will see your spark plugs.. 4 in this case.. You will have 6

    [​IMG]

    [​IMG]

    And begin to remove all spark plugs... The reason your remove all the spark plugs is because if you leave the plugs in, then the engine is not going to reach the desired cranking RPM, and so the readings will be lower.

    [​IMG]

    Now once you have removed the spark plugs, insert your compression tester and screw so its finger tight. Don't over do it.






    DO NOT START THE CAR... First you will need to either disconnect your CAS, pull out your Fuel pump fuse, or unplug ECU.. If you remove Fuel pump fuse, start the engine and allow it to idle until it runs out of fuel and stalls, repeat this three times to ensure all fuel in the system is gone.

    As mine is easily accessible, i unplugged ECU....


    [​IMG]
    [​IMG]
    So once done you can now try to start your car. I turned the key and ran each cylinder for the same number of revolution's, at least five to eight. That way, in each cylinder, the Piston can reach TDC (Top Dead Centre) the same amount of times to get a fair reading.. Do this and fully press in the accelerator.. Pressing the accelerator allows for maximum air intake. If you don't have the maximum available air going in, the results will be out, as its sucking against a closed throttle plate.

    Then go check over your result.. And jot them down

    [​IMG]


    Don't forget to release pressure by pressing the button below before you try your next cylinder.
    [​IMG]
    And then repeat till your done...

    [​IMG]

    [​IMG]

    [​IMG]




    So my results are....


    152
    151
    110
    120


    Not the healthiest of engines, but it has had the same oil for 4 years and been sat still for 3, lol. Will give her a good service and then try again.. But its pointing towards headgasket.

    The closer the numbers the better. Cylinder 1 and 2 show very good pressure. Would of liked them all to be near that, lol.


    To carry out a proper test you will need to take three or four pressure readings for each cylinder. Working on a warm engine with a fully charged battery!


    If your tests turn out not to be great, then do a wet compression test..

    A wet compression is carried out the same way as a normal test except that you pour 5ml of engine oil down each spark plug hole just prior to fitting the compression tester, allow about 30 seconds or so for the oil to settle around the piston rings and form a seal. Don’t forget to write down all three or four pressure readings for each cylinder. Compare the wet compression test results with the first set of test results.

    An increase in pressure indicates worn piston rings and/or worn cylinder bores, as the additional oil has acted as a seal.

    No increase in pressure points towards the camshaft or the valve gear and could mean any combination of: pitted or worn valve/valve seat, bent valve, worn valve guide, burnt valve or a worn camshaft lobe.

    No increase in pressure may also be due to an externally cracked cylinder head or externally blown head gasket this would be a little obvious though, as you should be able to hear it hissing/popping or see it bubbling.

    When your done re-fit all and tidy up
     
    #18 BillyBoy722, Jan 18, 2011
    Last edited: Jan 18, 2011
  19. BillyBoy722

    BillyBoy722 Member

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    well ive added pics but not sure if in the right order!

    this will really help
     
    #19 BillyBoy722, Jan 18, 2011
    Last edited: Jan 18, 2011
  20. r3k1355

    r3k1355 Well-Known Member

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    Always worth doing a wet and dry test if the numbers are off.

    Low results on number 4 can also be down to the battery flattening, hence why everyone told you to make sure the battery was a good strong one that was fully charged.
     
    #20 r3k1355, Jan 18, 2011
    Last edited: Jan 18, 2011

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