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bottom end knock...Help!

Discussion in 'Jeeps' started by Premierplowing, Nov 12, 2012.

  1. Premierplowing

    Premierplowing Member
    Messages: 40

    One of my Jeeps has developed a bottom end knock once the vehicle gets up to operating temp. Its most noticeable at low rpm, when shifting from forward to reverse or the opposite. Oil pressure does drop a bit at temp, down to 6-8 psi. But when revved, it jumps to where it should be. Any ideas on where to start to diagnose the problem? I'm thinking its either the oil pump or main bearing failure.

    Thanks for any input

    Tim

    1995 Wrangler Sahara 4.0/Auto
     
  2. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,114

    A knock shouldn't be caused by an oil pump failure, though damage caused by a lack of lubrication due to an oil pump failure certainly could. That would indicate two MAJOR (related) problems, and a potential for damage throughout the engine.

    Both the jeep's we've had (89 and 91) have exhibited oddities with respect to oil. Both oil pressure gauges would be pegged at all times while running. The 89 was sold mid 90's with an oil consumption problem of 1 qt per half hour highway driving. I acquired the 91 much more recently, and I intend to just keep running the thing until the engine completely self destructs itself, then replace the engine with something real. It sounds to me like yours may be ready for a new engine.
     
  3. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,552

    Engin Knock is not subject to shifting gears. Look for another problem IE bad motor mount , tranny mount....
     
  4. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,114

    It is subject to engine speed and load, which are affected by what gear you're in.
     
  5. Premierplowing

    Premierplowing Member
    Messages: 40

    The noise is apparant only when off the throttle WHILE at s changing gears or at an idle
     
  6. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,552

    Load and speed not changing gears something else going on
     
  7. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,552

    bad lifter ? the lifter is about midway down on the motor low oil pressure could cause knock at idle (doing bearing damage at the same time)
     
  8. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,114

    Just for academics sake, WHILE you're changing gears, the load is LOW. If a conrod bearing is worn, you could experience a piston slap knock at this moment.
     
  9. Premierplowing

    Premierplowing Member
    Messages: 40

    I'm fairly sure it's a rod knock. Its too loud and deep sounding to be a lifter noise which is a ticking sound. This is a beater jeep that we only use for residential properties and since winter is right around the corner , I just want to bandaid the problem to limp through the winter. Can I just put in new main bearings by pulling the pan?
     
  10. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,114

    My father did the rings on an '89 on his driveway. I was out of town at the time, but I know for fact that he didn't remove the engine. I presume that he must have accessed everything by pulling the pan.
     
  11. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,552

    Yes you can replace the main and rod bearings from under the jeep
     
  12. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,114

    One last thing I'd like to add... before you rip into it, be sure to get a second opinion from someone skilled who can actually be there to "experience" it. It really would suck to rip the engine apart and then find out that the bearings are all perfect.
     
  13. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,552

    i second that
     
  14. Mems

    Mems Senior Member
    from Maine
    Messages: 202

    Try a heavier weight oil as well. $15 worth of an oil change is well worth being able to see if some of the components are worn past their perspective "tolerances" and are now starting to create some knock in the engine compartment. Ultimately, yes the engine sounds like it needs a closer look, but the simple band aid of changing engine weight oil will give you a little better idea for cheap money.
     
  15. Premierplowing

    Premierplowing Member
    Messages: 40

    I ran 20w50 in it and it went away temporarily until the oil thinned out.
     
  16. basher

    basher PlowSite Fanatic
    from 19707
    Messages: 8,992

    You can access the bottom end thought the pan. I had this issue on the kid's 97 4.0L, when we dropped the oil pan we found pieces of piston skirt.:eek: My solution was a new long block, only cost about 2K total with us doing the work. Good to go for at least another 160KThumbs Up

    Quick fix attempt; Lucas oil additive.
     
    Last edited: Nov 16, 2012
  17. DieselSlug

    DieselSlug PlowSite.com Addict
    Messages: 1,054

    http://www.youtube.com/watch?v=CZH9CS-4pRw

    This was my old WJ. Bought it, drove it 700 miles delveloped a lifter tick type of sound then turned into a full blown knock. And this was already a replacement engine supposedly by P/O...
     
  18. Premierplowing

    Premierplowing Member
    Messages: 40

    I finally got around to getting the Jeep out of storage today. After getting it running I drove it around a bit to try to Reproduce the sound it made at the end of last season. The noise ended up coming from the transmission, It would only make the knocking noise when under a load. The fluid was a little low ...topped it off and the sound seems to have gone away.
    Any idea what was making the knocking noise?
     
  19. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,552

    U joint? else no clue on auto trans
     
  20. Premierplowing

    Premierplowing Member
    Messages: 40

    No cant be, I had one of my guys trying to find the source while i loaded the drivetrain with the brakes applied. Only made noise in R, D, 2,1... Not in park or neutral...I assume because it had no load on whatever was making the sound.