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Fhead Rpm

Discussion in 'Early CJ5 and CJ6 Tech' started by Jrobz23, Sep 16, 2020.

  1. Sep 16, 2020
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    How many of you guys ever spin these above 3200 RPM? If I have, it's maybe once or twice screwing around.
     
  2. Sep 16, 2020
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
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  3. Sep 16, 2020
    Jw60

    Jw60 Chim chiminey Chim chim cher-ee!

    Sedalia MO.
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    I've done 65 maybe 70 for a few miles with the 5.38s and 32s without Overdrive.
    It wasn't very happy about it but 1000 miles at 55 gets hot.
    3600 was about the top before valve float issues.
    3200 was typical for me.
     
  4. Sep 16, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    I take mine to 4K fairly often. I have to wind it out in first to make the shift to second when plowing up hill in high range. It starts losing power at around 4200 but will keep pulling until around 5k when it falls on its face.
     
    73 cj5 likes this.
  5. Sep 16, 2020
    GillaFunk

    GillaFunk New Member

    Bonner’s Ferry,...
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    I cruise at 2500
    I shift at 2800-3000

    however my engine has been completely torn down and overhauled professionally.

    above 3000, the engine sounds like it’s reviving pretty high
     
    Rick Whitson and mickeykelley like this.
  6. Sep 16, 2020
    73 cj5

    73 cj5 Not ready for the junkyard yet 2020 Sponsor

    Mississippi
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    Ready to put another set of rings in it? :lol:
     
    ITLKSEZ likes this.
  7. Sep 16, 2020
    GillaFunk

    GillaFunk New Member

    Bonner’s Ferry,...
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    Wow. That’s interesting.
    Now that I have OD, A Weber, and an improved ignition system, I haven’t found the need to rev it that high. Glad to hear the engines can spin like that.

     
  8. Sep 16, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    “Can” is different than “like to”
    :D
     
  9. Sep 16, 2020
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member 2020 Sponsor

    Denver, CO
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    Interesting to note that the willys graph Howard posted stops at 4000 rpm? Maybe you could finish the graphs?
     
    Glenn likes this.
  10. Sep 16, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    A high school buddy used to say, “The redline is just a suggestion.”
     
  11. Sep 16, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    The problem with high RPM in these engines is the long stroke. The rod velocity is high and puts a lot of strain on the rod bearings. If the oil film does not collapse, it should be fine. Not all of these engines are in top condition though. I would expect the side thrust on the piston is pretty high too, just from the geometry of it.
     
  12. Sep 16, 2020
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    4000-4500 for me in the sand dunes when I had mine.
    Yes, I had it balanced.
     
  13. Sep 16, 2020
    Mcruff

    Mcruff Earlycj5 Machinist

    Albertville, AL
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    The modern 107 ci Harley engine has a redline of 5500 rpm and it has the same stroke, albeit the oiling system on the Harley may be better than the F134 engine. I would say that with a little zinc modern oils in these older engines is a big help especially if the engine has been rebuilt well.
     
  14. Sep 16, 2020
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    Keep in mind how old some "used" f-heads are, and that the technology of the time made 60,000 miles a lifetime for an engine.

    This is another way of saying high rpms can blow the bearings out of a tired F-head. And a jeep in modern traffic is very easy to push too hard, unwittingly.

    I still remember the sound of that crankshaft knocking.... and the look on my father's face. :cry:
     
  15. Sep 16, 2020
    73 cj5

    73 cj5 Not ready for the junkyard yet 2020 Sponsor

    Mississippi
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    If you have a tired engine throw some 50wt and a bottle of oil stabilizer in it then send it. :twist:
     
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  16. Sep 16, 2020
    kenb

    kenb Member

    Detroit
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    M38A1 published cruise speed is 55mph which works out to about 3300 RPM. I won't run mine that high. Max cruise for me is 2700rpm. I usually shift below 3000. I live in a flat area though so I'm not trying for max power. My goal is engine longevity.
     
    Glenn likes this.
  17. Sep 16, 2020
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    I have parted out two race Jeeps with F134's. The first had the wrist pin pull out of the piston, and set in motion all kinds of carnage. This happened a little over 7100 rpm where it had been for over 5 minutes in the swamp buggy race.
    I still have another race Jeep engine that is intact and was regularly run up to 7200 rpm.
    Both these engines have custom ground Crane Cams, nearly 1/4" combined milled from the deck and head (piston crowns milled to pop-ups), roller rockers, and 4bbl carburation fed though the side of the head.
    Both engines have reletively stock cranks and rods, and still use cast pistons.
    If you think this is BS, let ITLKSEZ (Ryan) weigh in as he has experience with race built 134's. You will never forget the sound of an F134 at 7000 rpm!
    -Donny
     
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  18. Sep 16, 2020
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
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    Yell as loud as you can while gargling. That’s the best way to describe the sound. It’s pretty awesome.
     
    Fireball likes this.
  19. Sep 16, 2020
    mickeykelley

    mickeykelley Well-Known Member

    Republic of Texas
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    This is about my typical and mine was rebuilt professionally too. When cruising at 45-50ish, especially during the Texas summers, it gets a bit warm when done for miles. I’m right off the highway, so I don’t have much choice to get anywhere. Willy seems very comfortable at 30-35 mph.
     
    Last edited: Sep 17, 2020
    GillaFunk likes this.
  20. Sep 16, 2020
    kenb

    kenb Member

    Detroit
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