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Main Bearing Replacement

Discussion in 'The Garage' started by NerdBoy, Jul 2, 2004.

  1. NerdBoy

    NerdBoy 1/2 ton status

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    Is it possible to drop the crank out of a 350 and replace the main bearings, without pulling the motor?
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Yes, but only if you are on a budget, don't have much time, and can get the pan off without introducing dirt into the motor. I watched my friend and another guy put bearings in a 2wd Suburban once , the pan actually came out of that with little work. It can be done, if you really want to . I have never paid attention to how much room K trucks have though /forums/images/graemlins/k5.gif

    I don't recommend iy unless you have too /forums/images/graemlins/k5.gif
     
  3. NerdBoy

    NerdBoy 1/2 ton status

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    Pulling the pan off is not a problem at all on my truck. Did it 2 weeks ago to replace the oil pump. The engine is making a sound similar to a spun bearing, and I have checked everything else out. Am I going to have to pull the transmission to get the crankshaft out? I am on a tight budget, and I don't have the equipment to pull a motor out.
     
  4. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Well on that 2wd , they just slid the trans back and supported it. the flexplate/flywhheel will prevent the crank from dropping so trans needs at least moved back /forums/images/graemlins/k5.gif
     
  5. NerdBoy

    NerdBoy 1/2 ton status

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    So, if I am looking at the possibility of having to have the crank re-ground, it's probably just a better idea to pull the engine?
    Maybe I should start looking for a used 350 in good shape.
    I should probably buy a lottery ticket, too, then, as I really don't have the money for a new engine.
     
  6. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    As long as the journals are still good, you can get away with a cheap crank kit from somplace like PAW. Worst case scenario is the block will need align bored . You can probably find a rusted out running truck or car in Illinois cheaply and use the engine until you have more money /forums/images/graemlins/k5.gif
     
  7. ben427

    ben427 1/2 ton status

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    Just drop the pan and see how it all looks before you start friggin with yanking the engine. Rod bearings are easy to replace in situ, and you can even roll new main bearings in without dropping the crank at all if everything looks okay other than them.
     
  8. NerdBoy

    NerdBoy 1/2 ton status

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    I'll try that.
    I do have a question about that, though. If I pull the caps off, and don't see any bearing damage, should I just put the caps back on, and torque them to specs? Someone that was 90% full of BS once told me that they needed to be replaced if the caps get pulled off.
    Also, I am guessing that some plastigage would come in handy here, right?
     
  9. ben427

    ben427 1/2 ton status

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    If theres no apparant damage, just slam the cap back on and torque it up. Also, make sure you put the cap back in the same place, and in the same direction as it came off, seems simple enough, but people have messed it up.You wont need to plastigage if you use the old bearings again, but you should if you put in new ones, even though the crank is worn and clearance shouldnt be an issue.
     
  10. backcountry

    backcountry 1/2 ton status

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    If you have 4 bolt mains, remember the outside cap bolts should torqued different than inside bolts. I cant remember the torque spec though. /forums/images/graemlins/dunno.gif
     
  11. highrider_44s

    highrider_44s 1/2 ton status

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    hows the oil preasure /forums/images/graemlins/dunno.gif
    if you pull the mains off and they look good it wouldn't hurt to plastergauge one or two of them if i remember i had a motor with no oil preasure pulled the caps off and the barrings didn't look too bad threw some 6 thou palstergauge in to check didn't even squish it when we ripped her down pulled the crank out and the other half of the barrings were wore like a dirty old whore /forums/images/graemlins/peace.gif

    if you do roll some new barrings in you should also gauge them they should be about 2-3 thou /forums/images/graemlins/deal.gif if there not i think you can buy oversized barrings to make up the difference /forums/images/graemlins/dunno.gif /forums/images/graemlins/dunno.gif
     
  12. NerdBoy

    NerdBoy 1/2 ton status

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    Actually, the oil pressure seems to be ok. It seems a little low at idle, but, anything above idle seems good.

    I'm trying to track down a clacking noise in the engine, and this is the last thing I know of to check/replace. Just about everything topside has been gone over, already. I'm hoping that this is the problem, but I hope that there isn't any crankshaft damage.
     
  13. backcountry

    backcountry 1/2 ton status

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    Have you checked the fuel pump? /forums/images/graemlins/thinking.gif Mechanical fuel pumps can sometimes make alot of noise.
     
  14. backcountry

    backcountry 1/2 ton status

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    Could also be the water pump.
     
  15. NerdBoy

    NerdBoy 1/2 ton status

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    Checked the water pump, and all the other accessories.
    It could be the fuel pump. Hm.
    Should I look into putting a cheap electric pump on it, and a pump cover plate, to see if that is it? Or, do you have a better idea of how to check that?
     
  16. backcountry

    backcountry 1/2 ton status

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    Just remove it and check the shaft for wear and the arm on the fuel pump.
     
  17. diesel4me

    diesel4me 1 ton status Premium Member

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    I'd definately check the fuel pump too-I've bought a few good motors cheap that "rapped",turned out to be the fuel pump--also could be the timing chain slapping against the cover too,one motor I bought had the valve cover hitting one of the rocker arms and sounded like a bad death rattle,thought it was wrist pins or broken pistons,found that when I tried to tighten the valve cover bolts to slow the leaks and it got REAL loud!--took cover off and massaged it with a hammer,nice and quiet again!. /forums/images/graemlins/laugh.gif
    Usually if bearings are worn you get a noise like a woodpecker when you start it after sitting overnight,until oil pressure builds up.
     
  18. NerdBoy

    NerdBoy 1/2 ton status

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    It isn't the timing chain. Or the timing gears. I've had both, and the noise was still there.
    Maybe a better description of the sound would be useful. When it is cold, and idling really low, the engine almost sounds like a diesel. A rhymic "crunk" is the only way I can describe the noise. It's nothing topside, and it isn't detonation. I've been down those paths, and checked that stuff out. The only things I haven't checked, so far, are my bearings and fuel pump, that I know of. I plan to check the fuel pump this weekend before I start pulling bearing caps.
     
  19. backcountry

    backcountry 1/2 ton status

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    Almost sounds like piston slap if it only does it when it is cold. /forums/images/graemlins/dunno.gif

    Are you using forged pistons?
     
  20. NerdBoy

    NerdBoy 1/2 ton status

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    It's actually more noticable when it is cold because of the low idle. I just did a couple more tests. I'm pretty certain it is the main bearings. My oil pressure seems to be awfully low at low RPMs.
    According to the aftermarket gauge, it sits at about 5-10 PSI at idle, and up to about 2000 RPM. After that, it goes up to about 40 or so, gradually getting there as the RPMs increase. Now, I was always taught that 5-10 PSI with a brand new oil pump is low. Correct me, please, if I am wrong.
     

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