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Thread: Sleuthing a knocking 300 tdi

  1. #1
    Join Date
    Jun 2013
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    Orroroo
    Posts
    442

    Sleuthing a knocking 300 tdi

    Hi all,

    Just pulled the pistons out of my defender, it has had a knock since just after I bought it, maybe it had it before but has just got more noticeable over the journey.

    Anyway due too a clutch failure I've pulled the motor, it was still running fine, just knocking.

    Here are the pistons:

    Is this from overheating?

    There has been previous water ingression in the bores by the look of it,I guess before I owned it, as it doesn't use water or much oil really.

    And would this be enough to knock?
    I could have sworn it was a big end knock but did them a couple times with little change

    Cheers
    James

  2. #2
    Join Date
    Mar 2007
    Location
    Warwick Qld
    Posts
    1,858
    Quote Originally Posted by shack View Post
    Hi all,

    Just pulled the pistons out of my defender, it has had a knock since just after I bought it, maybe it had it before but has just got more noticeable over the journey.

    Anyway due too a clutch failure I've pulled the motor, it was still running fine, just knocking.

    Here are the pistons:

    Is this from overheating?

    There has been previous water ingression in the bores by the look of it,I guess before I owned it, as it doesn't use water or much oil really.

    And would this be enough to knock?
    I could have sworn it was a big end knock but did them a couple times with little change

    Cheers
    James
    Without seeing them in the flesh, I would hazard a guess that the engine has overheated at some stage.
    Assuming the pistons in the picture are from left to right, 1 to 4, number 1 has suffered the most, then progressively down from there.
    That would tend to point to the knocking being piston slap, rather than bearing knock. Not so much from piston wear, as from the rings losing tension.
    Seeing what, if any, scoring was evident in the bores would paint a better picture.
    Also, measuring the bearing gap, against the factory specs, may help.
    This doesn't necessarily mean overheating to the point of seizing, but probably not far off it.
    Depending on your plans for future use of the vehicle, either a comprehensive rebuild, or a set of rings and maybe bearings would be the solution.
    Hope that helps
    -----
    You have the right to remain silent. Anything you say will be misquoted, then used against you.
    -----

    1999 Disco TD5 ("Bluey")
    1996 Disco 300 TDi ("Slo-Mo")
    1995 P38A 4.6 HSE ("The Limo")
    1966 No 5 Trailer (ARN 173 075) soon to be camper
    -----

  3. #3
    Join Date
    Jun 2013
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    Warner Area - SEQ
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    1,421
    Funny... I've just had something very similar happen to me.... clutch failure, followed by removing the engine to replace the clutch and then looking at what else was needed doing while the engine was out... Well, that turned out to be a expensive idea in the end but at least I now know that the bottom end of the engine is in good order...

    What was done to the engine:
    > Removed the piston and it looked like they had gotten hot or something (see pics) - Block needed boring and new pistons and bearings bought
    > New Rear Main Seal
    > New Oil Pump gears
    > Ended up having to buy a new Camshaft and Cam bearings due to what looks like something causing damage to No.1 (see pics)
    > All new seals, etc
    > New Reconditioned Injectors





    Engine was seemingly running fine before Clutch failure, so I don't know how long it would have lasted... may have kept going ?? Engine has 362k kms on the clock
    Attached Images Attached Images
    Cheers.....
    Rob M


    Car-1: 1996 Discovery Tdi Auto
    Car-2: 1995 Defender Tdi 110 Wgn
    Car-3: 2009 Defender PUMA 110 Wgn
    My TRIPS: Rob's Triplogs and Trip Reports

  4. #4
    Join Date
    Jun 2013
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    Orroroo
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    Quote Originally Posted by donh54 View Post
    Without seeing them in the flesh, I would hazard a guess that the engine has overheated at some stage.
    Assuming the pistons in the picture are from left to right, 1 to 4, number 1 has suffered the most, then progressively down from there.
    That would tend to point to the knocking being piston slap, rather than bearing knock. Not so much from piston wear, as from the rings losing tension.
    Seeing what, if any, scoring was evident in the bores would paint a better picture.
    Also, measuring the bearing gap, against the factory specs, may help.
    This doesn't necessarily mean overheating to the point of seizing, but probably not far off it.
    Depending on your plans for future use of the vehicle, either a comprehensive rebuild, or a set of rings and maybe bearings would be the solution.
    Hope that helps
    I wasn't going to post these pics but they came out better than I thought:

    I've got another motor, supposedly 120k, it needs the timing/front covers replacing, I'm seriously thinking of dropping that in.

    And yes, it ran well with the bores looking like that!

    And yeah number 4 looks fine, the knock always seemed to come from number 3, it always abated somewhat when no.3 injector was cracked

  5. #5
    Join Date
    Aug 2006
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    Kingston, Tassie, OZ.
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    13,537
    100% that engine has been HOT.
    The Isuzu 110. Solid and as dependable as a rock, coming soon with auto box😊
    The Range Rover L322 4.4.TTDV8 ....probably won't bother with the remap..😈

  6. #6
    Join Date
    Jun 2013
    Location
    Orroroo
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    442
    Quote Originally Posted by justinc View Post
    100% that engine has been HOT.
    Yeah that was my take, just wanted back up!

    Amazing how well it went

  7. #7
    Join Date
    Aug 2006
    Location
    Melbourn(ish)
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    thats been hot to the point of the ally coming off the pistons.

    also known as the piston grabbing the bore.

    You know it got really hot when the ally is still fused to the bore. And yes, they'll run like that. not well but they run.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    TDI D1(parting/ed)
    Tdi autoManual d1 (Kept it for the girlfriend)
    Archaeopteryx 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
    If you think you're in front on the deal, pay it forwards.

  8. #8
    Join Date
    Jun 2013
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    Orroroo
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    We've also have a hilux that many years ago ran out of oil, the oil light wiring broke and the intake pipe got a hole in it during harvest when it was very dusty.

    End result was all nipped up, similar to this but much much worse, we ended up having to die grind the alloy off the bores at the bottom, and you would not believe how well it runs, still no power though.

  9. #9
    Join Date
    Nov 2008
    Location
    Black Mountain, Eastern Vic.
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    758
    I have a knocking 300tdi too. I could never decide what was causing it. I sounds like a big end but it is there hot and cold but only under load. Nothing like bearing noise in other engines I have had. Thought it might be a loose piston so I did a compression test.
    The pressures on cylinders 1,3 &4 were about 300psi which is expected with an engine which has done 300k km. Factory spec is 348psi. Surprisingly the pressure on cyl. 2 is 375psi. No idea why it is so high.
    Anyway I am replacing the crank bearing shells - needed because oil pressure is down to 100kPa hot.
    Don't think it will fix the knocking but you never know....
    Pics of the shells attached. Interesting wear pattern on 4 and 5 mains.
    Terry
    Attached Images Attached Images
    56 86" 2.0 P UK built, driven here overland.
    63 88" 2.25 P Canvas top. found in a hidden gully.
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.
    2000 P38 4.6
    2010 Guzzi 750

  10. #10
    Join Date
    Nov 2008
    Location
    Black Mountain, Eastern Vic.
    Posts
    758
    New std shells in. 0.05mm (.002") bigend journal wear, no measurable ovality.
    Hot oil pressure only came up to 200kPa hot. Pressure relief valve ok.
    Interestingly the knock is very much reduced, I can hear it probably because my ears are tuned to it. It would be lost in the general 300tdi clatter to anyone else I think.
    My theory is that no.2 cylinder with the high compression is working harder than the others and that was knocking the worn bigend. Can't think what else it could be.
    No.2 bigend shells were not any more worn than the others so I think I can live with it.
    Still don't know why the compression is so high.
    I might tighten the no. 2 exhaust valve clearance a bit for a short run and see if the compression leak changes anything.
    Terry
    56 86" 2.0 P UK built, driven here overland.
    63 88" 2.25 P Canvas top. found in a hidden gully.
    80 109" 2.6 P ex Army GS, saved from the scrappie.
    95 300tdi 130 Single cab tray.
    2000 P38 4.6
    2010 Guzzi 750

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