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6.9 rebuilding tips

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Mailbox, Dec 13, 2019.

  1. Mailbox

    Mailbox Registered User

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    I am rebuilding my 1985 6.9 IDI. I am looking for any tips, warnings, or suggestions for modifications. I am planning on a mostly stock rebuild. My priorities for this job in order of importance are:
    1. Dependable and long lasting engine
    2. Do it myself
    3. Save some money
    4. Improve gas mileage
    5. Increase horsepower

    About the truck:
    1985 F250, 4 speed, probably about 250,000 miles. Rumor has it the original owner used it to haul trailer loads of hay all over the state. It has a turbo on it made by Turbo Engineering that makes about 8 pounds of boost when the truck is working hard. I've had it for four years and it has always started easily and ran good. It has been smoking more and more and the power seems to be dropping of a little. It also has lots of oil leaks. Oil consumption got up to about 2 quarts per 20 gallons of diesel. A leak-down test showed pretty wide variation in the cylinders. I have the engine out and taken apart now. Cylinders are in spec. Heads are straight and sound. Valve guides are very loose and the valve seals were in bad shape. I'm having a machine shop replace the guides. Almost no visible wear on the bearings. Overall everything looks really good.

    About me:
    I have rebuilt a couple of gas engines but this is is my first diesel. My mechanical knowledge comes from 4 years of high school shop class and a couple of decades of fixing things myself. I have a pretty good selection of tools including a lathe and mill, though I can't call myself a machinist.

    Any tips, warnings, or suggestions for modifications will be appreciated.
    Thanks
     
  2. TahoeTom

    TahoeTom Supporting Member Supporting Member

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    Do you have press in or bolt in piston cooling jets? The switch was made on block # 237016. The press in style will make it difficult to hone the cylinders.
    One mod I made was to block off the coolant ports in the heads that are sealed by the valley pan/intake gasket. On the 7.3 the ports were sealed with cup plugs. My machine shop was able to mill them and tap to accept pipe plugs. DSC00109.JPG
     
  3. riphip

    riphip Supporting Member Supporting Member

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    Cainon and dgr like this.
  4. hce

    hce So can i.... Supporting Member

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    Not cheap, not necessary, balancing the rotating assembly. You may think the engines smooth, but once you experienced a balanced assembly its night and day. Also not necessary not cheap gapless ring really helps with the blow-by. I would also replace the rocker arm bolts, there a small size fasteners doing a critical job.
     
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  5. bbjordan

    bbjordan Snow Monkey

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    I like the idea of gapless rings like hce said, but ya, not cheap. I just went with the minimum end gap. Head studs are not cheap either, but they are probably the cheapest form of insurance for reliability, especially since you are running a turbo.
     
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  6. Oldiron

    Oldiron Full Access Member

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    @bbjordan if you dont mind can I get more info on the gapless rings? I am assuming less blow by? Less oil consumption?
     
  7. hce

    hce So can i.... Supporting Member

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    First of not a budget item, but may pay for themselves.. For the idi second ring is a two piece ring and when overlapped effectively make a solid ring. Nothing really special on cylinder finish needed, still had cross hatch on the cylinder when rebuilt so there was just a quick pass with the rigid hone. I believe the plateau hones were ran through as well. No break in period rings seated from the get go. Have about 10,000 miles so far so good, no oil useage, oil still goes instantly black when changed. As far as blowby, very little and just a light coating of oil in the cdr. Oil no longer accumulates in the cdr, banks turbo installed so the cdr does not drain. Less pressure in the bottom end should also help with oil leaks, I still have one spot on a valve cover fitting me. Some do argue that a 2nd gapless ring creates pressure between the first and second ring therefore hampering the performance of the first. I purchased just the 2nd ring from R&d and used a conventional ring set for the first and oil. Can purchase direct from total seal. More info at total seal
     
  8. CDX825

    CDX825 filtration nut

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    Whats the price for a set of gapless rings for one of these?
     
  9. hce

    hce So can i.... Supporting Member

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    R&d has them listed for 240 for just the second ring, complete total seal ring kit from summit 508. These are 7.3 prices. 6.9 are a special order from total seal, but should be close.
     
  10. bbjordan

    bbjordan Snow Monkey

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    Oldiron, what hce said ^^^. :D
     
  11. ColLonewolf

    ColLonewolf Registered User

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  12. jaluhn83

    jaluhn83 Full Access Member

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    Press in jets are not a huge issue, but you need to be careful removing and fabricate some tooling for install. Somewhat more risk in that you need to double check aim, but not impossible and wise to do even with bolt in.

    Update the rockers to 7.3 style (no bridge).

    Personally, I do not feel that gapless rings or balancing are worth the money. Blowby isn't inherently that big of a problem, and there's more risk in install/fitting with gapless rings. Likewise balancing - a super smooth engine may look pretty and feel better at idle, but no meaningful impact beyond that. Many things that can make it run a bit rough even with good balance also which would negate all the effort.

    Ceramic coating on the pistons is worth doing IMHO, especially for a turbo. I did this on my last engine (build with a HX35 & ~20 pis boost) and I credit it with reduced coolant temps and lifespan. That engine did suffer a cracked piston at ~80k miles, however upon teardown the oil jet for that cylinder was plugged and my best guess is that it had been plugged since the rebuild. That engine also suffered some chronic overfueling due to low boost (exhaust leak due to damaged piping). The other 7 pistons and the bore all looked great.
     
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  13. Mailbox

    Mailbox Registered User

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    Thanks for all the tips and the manual posting.
    I do have the press in cooling jets. I expect to ruin at least one of them so hopefully I can get new ones.
    I would like to balance my engine but I probably don't want to pay a machine shop to do it. Does anyone know an old school method to do it without a fancy machine?
     
  14. hce

    hce So can i.... Supporting Member

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    Talk to your machinist. Matching piston is easy, just a scale. One could make a setup to do rods. Matching the rods are the most time consuming. The rest really is all about the fancy machine and experience, especially if you want to see any significant improvement.
    post-1299-0-16577700-1501267448.jpg
     
  15. 1992 idi 73

    1992 idi 73 Registered User

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    There is a PDF like this that my dad found, its on my home computer but I'll try to find it for you. Its an entire tear down and rebuild service manual the Ford sent out. It has two parts one is about the chassis and the other just specific to all the engines.
     

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