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Thread: 3.9 Deck Clearance

  1. #1
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    3.9 Deck Clearance

    I have gone ahead and purchased a 3.9 to replace the 3.5 in the Range Rover. The 3.5 is very tired and I am pretty sure the camshaft is worn. Over the weekend I dismantled the 3.9 motor. Its a low compression, the crankshaft measured up ok and is useable, as are the pistons. I will replace all bearings, timing chain and gears, camshaft and lifters. One strange thing was the marks in no.1 cylinder wall, never seen them before. I took the motor down to my engine man this morning. We measured the deck height to bring it down to 0.010 to increase compression. All piston to deck measurements were 0.050 to 0.052 thou except for the front of piston no.1, it is 0.030, tried several pistons in the position and still got 0.030. After scratching our heads for a while we determined the liner must be in the block on a slight angle. Not sure how we are going to get around this. The carbon buildup in cylinder no.1 is consistent with the other cylinders, nothing to suggest there has been a problem, except for the marks in the bore.

    I am also going to replace the camshaft, there are many to choose from. Does anyone have suggestions on what lift and duration I should be looking around for or a grind you have successfully used.

    Block.jpg

  2. #2
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    I cannot answer your questions but while it is hard to see in the pic it, by the thickness of the liner at the top it looks as if you may have top hat liners installed but I cannot be sure.

    Garry
    REMLR 243

    2007 Range Rover Sport TDV6
    1977 FC 101
    1976 Jaguar XJ12C
    1973 Haflinger AP700
    1971 Jaguar V12 E-Type Series 3 Roadster
    1957 Series 1 88"
    1957 Series 1 88" Station Wagon

  3. #3
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    Sorry, probably should have made it clear that this is not the actual block. With a straight edge across the block all the liners are level.

  4. #4
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    if the deck is level, and all pistons measure the same length then it can only be the crank thats out ??
    "How long since you've visited The Good Oil?"

    '93 V8 Rossi
    '97 to '07. sold.
    '01 V8 D2
    '06 to 10. written off.
    '03 4.6 V8 HSE D2a with Tornado ECM
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    '16.5 RRS SDV8
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    1988 Isuzu Bus. V10 15L NA Diesel
    Home is where you park it..

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  5. #5
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    Not necessarily.

    Gudgeon pin in piston could be incorrectly machined, as could crown/skirt, crown could have collapsed on ring lands, many many reasons for a problem like that to exist, including little end incorrectly machined, or bent rod. Doesn't take much.

    but since o.p. stated many pistons express same result, need to ask if they were on different rods or the same rod each time.
    i.e. eliminate all variables where possible.

    Key is, you won't know until you pull the piston and rod and mic them up and check them for parallel bores on a surface plate.

    a bore that is not true will leave telltale signs on the gudgeon pin and the little end, especially with that kind of difference... should be highly visible wear pattern on the pin and in the little end bush.

    then there will be leading edge wear on the piston crown, perhaps scuffing, or a binding ring in a land.

    lots of things to look for and no answers available! - without a complete disassembly examination and precision measurements.

    iotw, noone here can give you an answer based on a picture and a description.

    insofar as cams... plenty of threads on here about them, have a bit of a rummage around and see what you come up with.
    Roads?.. Where we're going, we don't need roads...

  6. #6
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    wont be parallel bores on a 3.5/9, just big oval holes!, thats why they changed rods/pistons with the 4L,
    "How long since you've visited The Good Oil?"

    '93 V8 Rossi
    '97 to '07. sold.
    '01 V8 D2
    '06 to 10. written off.
    '03 4.6 V8 HSE D2a with Tornado ECM
    '10 to '21
    '16.5 RRS SDV8
    '21 to Infinity and Beyond!


    1988 Isuzu Bus. V10 15L NA Diesel
    Home is where you park it..

    [IMG][/IMG]

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