Reboring old 6.9 block

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Ethan Smith, Jan 10, 2018.

  1. Ddizzy77

    Ddizzy77 Registered User

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    Probably don't do a lot of idis, scared to touch it. I think you have a solid plan to do it yourself, if you have the time do it slow and build it proper.
     
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  2. Macrobb

    Macrobb Full Access Member

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    Yeah... you can make it work fine. Also, check if your aftermarket pistons(.040-.060" over) come with the pin shifted up .010" to account for decking. They might well; mine apparently did.

    The thing to check there is test-fit the piston and see how far it comes out of the bore at tdc. If it's over spec, the piston can be decked to compensate.

    Also, check valve recession on the heads(head deck to valve bottom surface). If it's out of spec, recess those valves until it's OK. You don't want the clearances too small there, either head side or block side.
     
  3. Ethan Smith

    Ethan Smith Registered User

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    Thanks man. I appreciate the advice. Think its worth looking for a new block so ive got a longer stroke on it or is that not gonna make a difference.
     
  4. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    The crankshaft is what gives you the stroke. They are the same between 6.9s and 7.3s except for the 7.3 with a Factory turbo. That one is different.
     
  5. Ethan Smith

    Ethan Smith Registered User

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    Good copy. Mine was fried so id have to get another. They said they had one but with them not comfortable working on it id rather just wait for an old tired block to come along and work with that. They didnt charge me for maggin it and inspecting it, which simultaneously makes me both incredibly grateful, and suspicious :idiot:
     
  6. G. Mann

    G. Mann Full Access Member

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    I just listened to a long time diesel engine re-builder who said, in his 25 yrs of building engines, every one that had cavitation issues that he tore down also had a failed engine ground strap. Engines with good grounds never had cavitation.

    That made sense to me, although I have no idea how to prove it... Just checked all my engine ground straps... cheap to do.
     
  7. Ethan Smith

    Ethan Smith Registered User

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    Yeah that makes sense. The machinist said electrolysis is what does the cavitating. Not sure how coolant additives help but i think they form a layer to dissipate the shock over a wider area and then through the grounds from the bore. Awesome to think that explosion within the block creates a small electromagnetic field around the chamber that needs dissipating.
    The block my buddy sold me had been sitting out for most of a decade, at least -Playme. Im not sure what kind of corrosion made its way to the inside of cooling passages but im gonna just wait for a tired old motor with a good crank to hapenstance upon me for a good price. Then turbo time!!!:peelout
     
  8. Ethan Smith

    Ethan Smith Registered User

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    My mistake, not through the grounds from the bore, but rather from the bore into the coolant, through the block to the grounds to be dissipated through the frames or wherever. On a microscopic level cavitation would look very wild. An explosion from combustion separating the coolant from the chamber and somehow creating minuscule sparks that corrode the walls of the chamber if the engine lacks proper coolant additives. additives.
     
  9. G. Mann

    G. Mann Full Access Member

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    A bore scope inspection of the block cooling passages would tell you if there is any cavitation. With the block hot tanked and the freeze plugs out... would be a quick thing to look, and put your concerns to rest.

    As for the cylinder bores.... Just did 8 sleeves on a 6.9 block and took it back to Standard bore.... Customer wanted it to be a "perfect 6.9" so spent the money.
    Studs and Turbo, etc etc etc..... Runs damn nice..... now he is breaking it in carefully, by driving it like a rented mule.. ;))
     
  10. Ethan Smith

    Ethan Smith Registered User

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    Woah lucky guy! Bet that sounds sweet. I cant wait to build a freshy but boy moneys getting tighter these days. So here i am in the woods hunting down a relic! :smoke:
     
  11. Ethan Smith

    Ethan Smith Registered User

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    Shoot and hes just now driving it like its rented? Ive been doing that on my 85 since i got it like every bump costs me ten dollars! Which it does!
     

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