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M38A1 distributor replacement

Discussion in 'Early CJ5 and CJ6 Tech' started by Mike C, Dec 20, 2014.

  1. Dec 20, 2014
    Mike C

    Mike C Member

    Austin, TX
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    Feb 19, 2007
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    I swapped out the converted 24v distributor on my A1 to use regular plugs and wires. I swapped in a WWII distributor that I had on the shelf, but I can't get enough advance out of it. Any advice? Is it possible to re-clock the housing somehow? This is easy on a later GM motor where you can move the distributor 90 degrees but doesn't seem obvious to me here.
     
  2. Dec 20, 2014
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    The WWII distributer is for what engine?
     
  3. Dec 20, 2014
    Mike C

    Mike C Member

    Austin, TX
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    It's the F-head motor in my A1.
     
  4. Dec 20, 2014
    gunner

    gunner Member

    Washington state...
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    Dec 4, 2012
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    Mike, I have a 4008 on my F-head, and the original 24v dist is in a box. The PO had converted to an alternator, but left the original dist in it.

    I picked up the 4008 from Oldtime a few years ago and it works fine. Doesn't have a vacuum advance- only mechanical, but you can quickly ID it since it's the one with the dust cover under the cap and covering the points/condensor). I think the 4008 is what the WW2 jeeps had. Ken (Oldtime) could tell you , maybe he'll reply.

    The CJ3B page has some good write-ups on the F-head systems, including the distributor
     
  5. Dec 20, 2014
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Aug 3, 2003
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    To reclock an F-head distributor would require removing the oil pump and resetting it, to shift the driven gear at the teeth on the cam.
     
    Last edited: Dec 20, 2014
  6. Dec 21, 2014
    Mike C

    Mike C Member

    Austin, TX
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    Thanks guys. It looks like I have one of 2 different styles. One has a plate on the bottom that controls total rotation on the distributor (mine) and the other uses a clamp that allows rotation of infinite degrees. I'll look at some of the parts I have and see if I can scrounge one of those, or as noted, clock the oil pump another tooth.
    Thanks guys.
     
  7. Dec 21, 2014
    flatyfreek

    flatyfreek Member

    Hillsburrito, OR
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    Dec 17, 2013
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    How hard is it to modify the plate for more advance, maybe even make a new one with longer slots? How far off are you?
     
  8. Dec 21, 2014
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    That plate can be mounted two different ways, and will effect timing a lot.

    One other thing, the F-head was not a WWII engine, which is why I asked, The WWII engines were flatheads and had either a gear mesh drive between the cam and crank (early) or a chain drive (later). Not sure what year the change was, and do not remember how that effected direction of rotation for the rotor.
     
  9. Dec 21, 2014
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    With a chain drive wouldn't it be opposite of gear driven rotation?
     
  10. Dec 21, 2014
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    You would think so. If memory serves, the drive gear for the oil pump in the mesh one is opposite of the one for the chain drive. The drive gear on the pump correspondes, or the whole pump does. So that the distributer spins in the same direction for all engines. I think.
    I'll have to find all my ECJ books and look it up again. I've moved, and do not know which box in the garage they might all be in.
     
  11. Dec 21, 2014
    Mike C

    Mike C Member

    Austin, TX
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    I knew the chain/gear factor was in play but never pondered the end result. My MB has a later L-head in it, so I don't know if chain or gear. It will be easy to flip the plate or possibly fab a new one so I'll look at that. Jeep at the farm and not my house so can't ask questions and look at it at the same time!
     
  12. Dec 21, 2014
    1960willyscj5

    1960willyscj5 Well-Known Member

    Mesa, Arizona
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    I know about the plate reversal thing because one of the PO's installed it wrong on my '60. Made timing real difficult, because the oiler on the side of the distributor would hit the block and not allow full swing of the timing until that plate was turned over. Made a big difference.
     
  13. Dec 21, 2014
    tcfeet

    tcfeet Member

    east of west,...
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    May 30, 2009
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    It is my understanding the M38A1 came out in 53, and it had the F Head engine in it.
    A friend has a 53 model, and it has the F Head in it also..........
     
  14. Dec 21, 2014
    Mike C

    Mike C Member

    Austin, TX
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    743
    The M38A1/CJ-5 exists only BECAUSE of the F-head motor. The short cowl of the CJ3A/M38 wouldn't fit the taller profile of the F-head motor. Same reason the 3B exists. Mine is just over 20,000 serial # and is a 1952. It had the early fenders on it as well when I got it but they were damaged. I have a 1953 as well, and it has the later fenders. M series vehicles had completely waterproof electrical systems and were the military standard 24v. The distributor had a coil built into it (similar to an HEI but watertight) and it had plug wires that screwed to the cap as well as to the plug to maintain the waterproof capability.

    But I have no need for 24v or waterproof ignitions. I'm happy with the 12v conversion, a 10si alternator, and just one 12v battery. Especially considering the former owner had converted the distributor by just knocking a hole in the cap and running an external 12v coil and it still had 60+ year old plug wires on it.
     
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