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304 Oil Pump

Discussion in 'Intermediate CJ-5/6/7/8' started by Allan, Jan 3, 2020.

  1. Jan 3, 2020
    Allan

    Allan 74 Renegade

    Olympia
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    I know that there are tolerances for the oil pump, I know it needs packed with petroleum jelly if rebuilt or tore down and put back together, Before I decided to rebuild the engine because it was smoking like crazy,( likely because of sticky oil rings), I was getting about 30 psi, not sure on volume. The motor is surprisingly clean as a whistle inside, 60,000 miles on odo. I felt that that’s a pretty reasonable pressure given the above mentioned. My question is should I rebuild the pump using a crown kit, or should I just put it back together with the old parts, new gasket. I don’t think you can get better than the stock gears ect. The aluminum is in good shape, gears aren’t bad, I’ve heard rebuilding them can sometimes make things worse if it’s not necessary. Or is there a more modern oil pump for these available?
     
  2. Jan 3, 2020
    73 cj5

    73 cj5 Not ready for the junkyard yet

    Clinton, Mississippi
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    I wouldn’t buy crown engine parts given their reputation. Bull tear has amc engine stuff. Melling probably has oil pumps for them.
     
  3. Jan 3, 2020
    sterlclan

    sterlclan Member 2022 Sponsor

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    I would be sure the filter adaptor is smooth where the gears ride on it and wouldn't use crown parts. get a better quality set of gears from the flaps if you choose. I cleaned and smoothed all the oil ports in the timing cover and the matching ones on the block,used stock gears and a bulltear filter relocating kit. gained 20 psi hot runs about 50 when hot and better than 30 hot idling. I still surface sanded the bulltear part to get a smooth surface. look for the blueprint 225 thread for an example of the type of oil passage clearance work im talking about. that info is for a v6 but very similar to our amc pump set up.
     
  4. Jan 4, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    30 psi under what conditions? A good rule-of-thumb is a minimum of 10 psi of oil pressure per thousand RPM. The cold oil pressure is meaningless since the oil thins out as the temperature comes up. You want to look at the hot idle oil pressure (HIOP) at full operating temperature. The HIOP is especially telling for these engines. If you see 30 psi at hot idle, you have good pressure. It should come up on the highway.

    Also, the original equipment electric oil pressure gauges aren't the most informative choice. Response time is really long, they are not very accurate (my impression), and they seem to fail a lot. IMO I would get rid of the factory gauge (if you have one) and replace it with a good quality mechanical gauge, say Stewart-Warner or Autometer or similar. Lots of discussion of this in old posts here.

    If you have low HIOP, it could be the timing cover, but it could also be the rod bearings are worn out, or you could have bad cam bearings (common - the originals are prone to delaminate). So fair warning, you might spiff up the timing cover and not fix your HIOP problem, if you have one. But the timing cover is on the outside, so that's a good place to start.

    A lot of experience with these timing covers, both original and Crown, on the Wagoneer/J-truck sites. The upshot is you are way better off to recondition the cover you have rather than buy a new one from Crown or wherever. No guarantee that the clearances on the Crown cover are correct, and the machining can be badly aligned on the Crown covers. So you end up blueprinting (and possibly rejecting) the new Crown cover, just like you would the original cover.

    The main issue is the end clearance between the gears and the oil filter adapter. This is critical, and covered in the TSM. The gears sit proud of the body, and the oil filter adapter gasket provides the minimal clearance. Here's a good thread to look at: V8 timing cover/Oil pump refresher. pic heavy. - International Full Size Jeep Association

    IMO the passage enlargement and stuff is race-car tech and not central to the issue. You'd be fine to follow the above thread and the TSM. I also am skeptical that the oil pump "rebuild kit" does anything, since it's the aluminum timing cover that wears. You get mostly the parts you don't need in the "rebuild kit."
     
    Last edited: Jan 4, 2020
  5. Jan 4, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Also, since you have the distributor out, word is you are better off to prime the oil pump with a priming tool rather than pack the pump with petro jelly. Easy, and no extra goop added to your oil.
     
  6. Jan 4, 2020
    Allan

    Allan 74 Renegade

    Olympia
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    Thank you great info, what I mean by the conditions are the engine wear that you spoke of.
     
  7. Jan 4, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    NP! By conditions I meant test conditions. Hot, cold? Fast, slow? Idle, highway? 30 is really low for cold on the highway but good for hot idle. Type of oil and filter will matter too.
     
    Last edited: Jan 4, 2020
  8. Jan 4, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    If you have the engine apart, be sure to measure the gear clearance when you assemble it. This is shown in the TSM. There is no guarantee that the new gasket will be the same thickness as the old, and the end clearance is determined by the gasket. Too loose and you'll have no oil pressure. You can buy thinner gaskets, or do the lapping routine shown in the link I posted above.
     
  9. Jan 5, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb

    Southern...
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    This is good write up. I learned a lot. Especially with the link to the FSJ write up and pictures. I noticed it was mentioned in the Jeep TSM that there is clearance tolerance of .0005 to .0025 for the gear teeth to case clearance inside the gear case bores. Do the gears and their respective shafts and shaft bores not usually wear? I did not see this mentioned as the cover and end of gear clearance seemed to be of the most concern. Am I missing something? Thanks Jim
     
  10. Jan 5, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    The sides of the gears are not in direct contact with the aluminum cover, so there should not be significant wear there. Anyway, the side clearance of the gears seems to not make much difference to the resulting oil pressure, compared to the end clearance. I would expect all moving parts to wear to some degree. Experience shows that the main location for wear that matters is the end clearance of the gears. It seems clear that this wear is almost entirely in the aluminum timing cover and oil filter adapter, not the hard steel gears.

    My understanding is the shafts of the gears and their bores don't wear much. The driving gear shaft that connects to the distributor is pretty long, and does not wear down the cover much. The driven gear rotates on a steel shaft stationary in the timing cover, so its axis is steel-on-steel, and would not wear much.

    upload_2020-1-5_7-18-14.png
     
    Last edited: Jan 5, 2020
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  11. Jan 5, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Here's another thread about the timing covers and timing gears, and how to blueprint an aftermarket replacement cover: Timing cover & chain sets ?? - International Full Size Jeep Association

    SC/397 is a pro engine builder and I believe he is a presence on the AMC boards as well.

    Quote from that thread - "Buick oil pumps are like AMC oil pumps but even stupider." :lol:
     
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  12. Jan 5, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb

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    Ah, Thanks for the additional text and link. I am now getting a better understanding of how things work. It makes sense now that the gear to cover clearance is the most critical tolerance. Just had another thought,( I know that's dangerous) would it work to use plasti-gauge to check clearance when lapping and fitting the cover, when you get close, just lay it on top of the gear and place new gasket on and torque down the cover remove and measure. what do you think?
     
  13. Jan 5, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Sure. (y)

    upload_2020-1-5_14-9-16.png
     
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  14. Jan 5, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb

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    Thanks, feel confident I can rebuild my pump now with success.
     
  15. Jan 5, 2020
    nickmil

    nickmil In mothballs.

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    I would recommend both packing the pump cavity with petroleum jelly and use a tool to build oil pressure before initial startup. The idea of the jelly is to lubricate the pump but more importantly to create a suction when the pump gears are turning to draw the oil from the pan into the pump. Without it you chance running the pump dry damaging it and possibly never drawing oil into the pump. I’ve seen it happen on both Buick’s and AMC’s. It’s such a simple thing to do it makes no sense not to and is good insurance.
     
  16. Jan 7, 2020
    johneyboy03

    johneyboy03 The green beast

    Quebec, Canada
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    Bulltear is on the point. Bought their nickel plating cover along their midplate is giving me real good result. Also they have a .07" gasket to have the better end clearence possible. I also gave a try to their relocation oil filter kit only to find a loss in pressure ( all the fiting and hoze added kill the pressure).

    I have around 10-15 psi on idle and it will right on the 10psi/1000rpm range when reving. no problem ever since.


    Only thing with bulltear...you have to work you patience since amc part are more a lobby than a full business. But once you get the product you'll be a happu customer.
     
  17. Jul 13, 2020
    rusty72cj5

    rusty72cj5 Member

    Florida
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    Allan, just wondered if you decided to pack the oil pump with petroleum jelly or just spin it with the drill techniques to prime it before start up and how it went for you. Almost to that stage in my 304 rebuild as well. ‘72 TSM and Haynes both say pack it with petrolatum but would rather not if not necessary. Only thing is mine will sit for a little while after rebuild is completed before I actually get to the point of cranking it.
     
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  18. Jul 13, 2020
    Allan

    Allan 74 Renegade

    Olympia
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    We are in the same boat, I am not sure what my engine rebuilder did but they are the best in town, I’m sure it was jelly if I remember correctly, I had mine rebuilt, and mine too will sit for a year before I get the body and new electrical done. I will use a drill and will do at low speed for sure, it isn’t turning that fast to begin with, I also put the bypass block in from Bull tear.
     
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