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Thread: Onto the conrod bearings (TDI)

  1. #1
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    Onto the conrod bearings (TDI)

    I've got the sump off, dropped the ladder frame (200 TDI), looking at the big end bearings.

    With a motor that's done ~500k and starting to get low oil pressure at hot idle, I am mentally preparing myself for an engine out rebuild. But if I am lucky and crank is in good nick this will be a sump off/on job to get back on the road ASAP.

    I have big end shells #1 and #4 out, and so far so good. Certainly over due, but crank is smooth. I know there are measurements to observe but I'm on my back without a micrometer so I am going to go by eye/feel/sound on this one.

    Now waiting for the replacement bearings to arrive.....

    Should I need to take the engine out I will do it all by the book, BUT whilst I have sump access is it worth replacing just the lower MAIN bearings on caps 1 - 4?

  2. #2
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    You can usually get the upper shells out too, just refashion a suitable split pin to fit into an oil hole in the crank and stick up about 3mm, then rotate the crank to push out the shell. Same maneuver to get it back in.

  3. #3
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    Do em all one at a time
    I did my 300 in situ i just pushed them out from the opposite side enough to grab with some pliers easy as to do
    And i mean the (Big Ends) the main`s should be fine as they don`t cop a hammering like big ends

  4. #4
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    My only concern with playing with the mains is disrupting the flaky rear main seal/ t-seals
    10:1 if you don’t have a leak now you will soon after!

    I’ve only stripped a few high mileage 300s and on them the Conrod big end shell wear far exceeded the mains. In light of minimal wear on the shown shells I would be thinking of not touching the mains

    Steve

  5. #5
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    1 and 4 conrods done. Onto 3 and found this (see photo)

    First four shells out the bag were as expected and fit fine (plastiguaged), the last four have a hole in them. What have I got here?

  6. #6
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    First things first, never replace one half of a bearing! All the oil will tend to migrate to the loosest part, and starve your nice new bearing shell of lubrication, ensuring its' early demise.

    The hole is for oil to flow through onto the bearing face.

    The tab is to locate the bearing shell within the conrod big end. If you are only replacing the bottom shells (bad idea!) then those shells are for the top side. Push a conrod and piston up the bore a bit, and you should see the cutout and oil hole in the existing shell. The shells can only go in one way, due to the tab.
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  7. #7
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    Erm, look at my earlier photo of 1 + 4 bearings removed. No holes top or bottom.

    The last four shells in the bag were inline to service conrods 2 + 3, but they have bloody holes in them. Ive got the wrong set clearly.

  8. #8
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    OK so I ordered RTC2993 for my TDI but it looks like I received bearings for a 2.25 diesel (RTC7139)

    The 2.25 bearings have the hole on the upper bearing shell, the 2.5's are solid uniform.

    Supplier is telling me that I have the best bearings for the job, that the hole is of no consequence, and that I should install the holed bearing in the bottom position.

    What do you lot think?

  9. #9
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    Quote Originally Posted by donh54 View Post
    First things first, never replace one half of a bearing! All the oil will tend to migrate to the loosest part, and starve your nice new bearing shell of lubrication, ensuring its' early demise.
    In a hydrodynamic bearing the shells shouldn't touch the journal, the load is carried by the oil between the surfaces.
    The only time it should touch is on startup (no oil pressure). A worn shell bearing creates a bigger gap so the oil flows out more freely so you run lower oil pressure, plenty of lubrication but might be possible for the surfaces to make contact.
    The 'white metal' (Babbitt) surface is soft and any particles get embedded, long term the white metal is worn away down to the copper backing.
    The Science Behind Modern Performance Engine Bearings

    But I'd agree, you only change both halves of the bearing.


    From the supplier's comments the 2.25 has oil squirters in the conrods hence the hole to let oil up the conrods, doesn't the 200TDI have them ?? Looking at your pictures it doesn't so the supplier has suggested putting the ones with the holes in the caps so you get a full surface area in the highly loaded shells in the conrod. If they are exactly the same size I can't see a problem.


    Colin




    Colin
    '56 Series 1 with homemade welder
    '65 Series IIa Dormobile
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    '76 SIII 88" (Isuzu C240)
    '81 SIII FFR
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    Motorcycles :-
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  10. #10
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    Its of no consequence in a tdi... however in a 2.25 that hole MUST be there😅
    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..😈

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