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Thread: 5D55 Compression failure after new 4D56 head and new headgasket installed.

  1. #1

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    Offline
    Join Date
    12-27-2015
    Posts
    4
    Location

    Chico, CA
    Vehicle

    1983 Mitsubishi Mighty Max
    Engine

    4D55-T

    5D55 Compression failure after new 4D56 head and new headgasket installed.

    Hi all first time posting on the forum. So I have a 1983 mighty max turbo diesel, and recently the head gasket went out. I pulled it all apart to find a pretty badly cracked head. After some research i ordered a new 4d56 head complete with cams and valves. Also put in new injectors, thermostat, water pump, fuel pump and had the radiator pressure tested and flushed. I have it now back up and running, but it is running quite rough. I figured i had made a mistake with the timing or something since this is the first head gasket or timing belt i have done. I had the truck towed down to my mechanic who knows these trucks quite well. He said that the timing is set right but it failed on the compression test. Cylinder 1 and 4 are about 30 psi low and cylinder 2 and 3 are 120 psi low. So far we have not been able to come up with a cause other than bad piston rings, which i am really hoping it isnt. I contacted the guy from whom i got the head to make sure there couldn't be a problem with the combustion chamber size in the new head or anything else with the new head. Only things he could think of was at it being a timing issue or piston rings. My mechanic is going to check the timing further tomorrow but is pretty certain it is correct. It seems odd to me that the cylinders 1 & 4 and 2 & 3 are equally losing compression if it is the rings, but that could still very well be the case. If anyone has any ideas of what could be causing i would greatly appreciate the input, thanks for reading!

  2. #2

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    09-10-2016
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    5
    Location

    Olga Wa
    Vehicle

    1983 Mitsubishi Mighty Max
    Engine

    4D55-T
    Hi, I am brand new to this particular engine but have quite a bit of experience with engines in general. Often when two adjoining cylinders are bad it is a problem in the sealing (or gasket) between the two. I feel your pain.....

  3. #3

    Array
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    Offline
    Join Date
    01-18-2015
    Posts
    153
    Location

    Inwood WV
    Vehicle

    1991 Mitsubishi L200
    Engine

    4D56-T
    Find out if he tested 2/3 with all glow plugs out.
    Sounds like either gasket between 2/3 or you need to adjust the valve lash

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