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D8N engine rebuild. Couple of questions.

Discussion in 'Dozers' started by Alberta Cowman, Jan 8, 2020.

  1. Alberta Cowman

    Alberta Cowman Active Member

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    My D8N 9TC02252 was getting exhaust in the coolant. Pulled the head and the head gasket fire ring was blown out on #6. Sent it it to be resurfaced, magnafluxed and valves replaced.

    The liners had no crosshatch left so we were hopeful of getting away with an inframe. We dropped a rod and a main cap and the bearings were pretty rough and the crank had a few minor scratches so we decided to do a complete rebuild. Still waiting on word on the crank. Hopeful for just a polish.

    Just looking over the oil pump gears and they have an abnormal wear pattern to them. This has the two section pump setup. The rear 1/3 to 1/2 of the gears in the main pump body have more wear than the forward portion of those gears. The scavenge pump gears appear to have more uniform wear. I can still see the machining marks on the gears except for where they are polished. They are smooth and look good otherwise. Just wondering if the abnormal wear is anything to be concerned about?

    Also seeing as I have the torque converter out is there anything I should check or replace on it while it's out? Was running good when we took it down. It's my first time dealing with one so I'm a little unsure.

    First pic is of our fun so far. I think we reached the end of our troubles hopefully. Second is a scavenge pump gear. Third is a main pump gear. Fourth is a rod bearing. Think we were on borrowed time.

    Thanks image.jpeg
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  2. Nige

    Nige Senior Member

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    First question - how many hours on the engine and the converter and has either of them ever been rebuilt before.?
     
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  3. Alberta Cowman

    Alberta Cowman Active Member

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    Hi Nige.

    The hour meter says 12,500. I bought it two years ago and have put about 600 hours on it. Not sure if the meter has been changed as that seems too low.

    I don't really have any history on it. The engine bearings were OEM and don't have a date stamp so I'm unsure if they've ever been replaced. It was odd in that the main bearing caps weren't numbered so I assume they haven't been off?

    There was paint on the gasket edge between the block and flywheel housing and no chipped paint on the external bolt heads so I don't believe the crank has been out of it before. The head had no paint so it has been replaced or rebuilt some time previous.

    Not sure about the status of the converter. I didn't see any obvious signs of it being replaced/ rebuilt. Not sore what an average life span of one would be?

    I bought it as kind of a project. The undercarriage was nearly shot and it was hard starting. I put all new Cat rails, idlers, rollers, segments and several bogie pins on it a year ago. It was a fair bit of fun to pull the engine and TC so I'd like to do this right and really appreciate all the experience such as yourself on here.

    Thanks.
     
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  4. John C.

    John C. Senior Member

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    I used to always to do a tear down and inspect on the converter when I had the engine out. I’ve found the vanes on the stator starting to loosen and change their angles. The oil wasn’t heating yet but was close showing a big problem. It doesn’t take long to tear them down and bearings and seals aren’t that expensive. The three critical and expensive parts are the impeller, turbine and stator.
     
  5. Nige

    Nige Senior Member

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    I’d agree with John. The converter is out, tear into it and reseal it at the very least. Maybe new bearings as well.

    If you look at the back side of the crank bearings you should find a 6-Letter Code. It might look something like UNDDNN. Post that code and Information is available to date the bearings. With that and the date of manufacture of the tractor it should be possible to determine if the bearings are original or not.
     
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  6. Mobiltech

    Mobiltech Senior Member

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    I would at least reseal converter and inspect metal seal ring retainers closely.
    Those oil pump gears don’t look bad but watch out for wear in the bearings and shaft surface of the oil pump.
    While you have the trans pump drive shaft off now would be the time to at least replace the trans pump input seal.
     
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  7. Alberta Cowman

    Alberta Cowman Active Member

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    I couldn't find a 6 letter code on the bearings. On the rod bearings I found a 5NMOO O

    On the main bearings there's a
    5 NEOO 13 (lower half)
    5 NROO 3 (upper half)
    image.jpeg
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  8. DMiller

    DMiller Senior Member

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    At least nice and clean, bearing shell erosion usually indicates coolant in oil(Acidic metals removal to cavitation erosion(Steamoff), doing it right full out of frame and cannot agree more converter is out go thru it.
     
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  9. Alberta Cowman

    Alberta Cowman Active Member

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    Thanks guys.

    I read through the converter disassembly and reassembly and it doesn't appear to require any special tools.

    I don't think my micrometers are big enough for measuring the stator flange and impeller wheel flange. Should I be finding some larger ones?
     
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  10. Mobiltech

    Mobiltech Senior Member

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    If you can see machining lines on edges of mating surfaces you probably wont need to measure them.
     
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  11. Alberta Cowman

    Alberta Cowman Active Member

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    Didn't know what to expect or look for as I've never opened one up before.

    Thanks for the tip.
     
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  12. Mark250

    Mark250 Senior Member

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    Hi,we had a lot of trouble with #6 piston seizures on the early D8N, at one stage we were using a different part number piston from memory than what the parts book indicated
    Cat later put out a service bulletin covering this topic and what to do about it.
    i don't have the resources any more to see if this is still a problem but looking on SIS there are still references to this issue
    Mark
     

    Attached Files:

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  13. Alberta Cowman

    Alberta Cowman Active Member

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    The oil pump shafts look good yet. The bushings show some scuffing so I'm going to replace them.

    The transmission pump looks to have been changed fairly recently. The couplers on the transmission pump drive shaft are cracked so I'm going to replace them. And a bunch of hyd hoses that are original yet I believe.

    Thanks.
     
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  14. Mobiltech

    Mobiltech Senior Member

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    Just 3 small bolts gets you the input seal holder and bearing off the pump. I’d still check the lip seal if I were you.
     
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  15. Alberta Cowman

    Alberta Cowman Active Member

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    Funny you mention that #6 was giving issues. On mine #6 had a head gasket blow out and the piston rings were broke in a couple pieces yet the other 5 pistons were good.

    I'll have to check with my machine shop as far as what piston/liner assemblies they ordered.

    Did you upgrade them to dual piston cooling tubes?

    Thanks for the heads up.
     
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  16. Alberta Cowman

    Alberta Cowman Active Member

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    Sounds simple enough maybe I'll add it to my parts order and do it just to be safe.

    What part of Sask are you at? I'm an hour west of Edmonton.

    Thanks.
     
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  17. Nige

    Nige Senior Member

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    Regarding Date Codes on the crankshaft bearings, they are marked with only month and year rather than day, month, and year which is what I was originally thinking would be the case.

    NEOO translates as March 88, NROO as April 88, NMOO as February 88. With the build date of the tractor being May 1988 I am of the opinion that these are the original crankshaft bearings.
     
  18. Alberta Cowman

    Alberta Cowman Active Member

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    Thank you.

    I definitely learned something today.
     
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  19. nicky 68a

    nicky 68a Senior Member

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    I fitted a new complete oil pump to my D8R motor even though the one in it wasn’t the worst I’d seen.
    Cost about 1000 US dollars from ITR non oem.
    I also fitted all new Cat hoses that run from the tank down the chassis to the front.
    Another 1000 but well worth it while you have acess
     
  20. Nige

    Nige Senior Member

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    Agreed. For the value of everything else that's will be installed in it a the cost of a replacement engine oil pump is small beer in comparison.
     
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