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350 runs for 20 seconds..then horrible moaning/rubbing sound??

Discussion in 'GM Powertrain' started by Big6ft6, Nov 14, 2008.

  1. Big6ft6

    Big6ft6 New Member

    Please help diagnose my sound.

    This has to be something pretty bad.

    I have a freshly rebuilt, bored, TBI 350.

    During the intial start up and cam break in I boiled over the coolant, but shut the carn down quickly.

    Now (after fixing the cooling problem) when I start the engine it will run great for about 20-40 seconds, then a very loud metal on metal rubbing/moaning sounds come from the engine. Of course I immediately shut it down.

    I can restart the engine and it will repeat, run great 20 seconds, then same thing. The sound is horrible, vibrates the truck.

    I have very high oil pressure (gauge ends at 60 psi and gauge stays pegged) I'm not the person who had the engine rebuilt so I don't know if a hi-volume oil pump was used.

    Something is clearly heating up in the engine and then losing tolerance and rubbing.

    I assumed a spun bearing, but after reading a bit sounds liek spun bearing makes clicking noises and cuases low oil pressure? This is definitly not clicking and I definitly don't have low oil pressure.

    What could this be? Does my high oil pressure mean my oil is blocked from getting somewhere?

    The engine must be trashed, becuase the first time I ran the engine I made it through 10 minutes of the cam break-in before it over heated so if something was starved for oil, it is ruined by now.

    Any ideas?
  2. retired

    retired New Member

    You didn't do the high idle cam break in did you? Sounds like the motors toast, spun bearing. don't feel bad I did it once myself.
  3. Big6ft6

    Big6ft6 New Member

    Yeah, everything I've read says it is critical to do 20-30 minutes at 1500-2000 rpm including instruction from the engine builder (I have a flat tappet cam)

    So I did this before I had the flywheel even hooked to the torque converter so the engine should've been load-free. But I only got 10 minutes through before the radiator started puking engine coolant.

    I thought of a good descriptor of the noise I'm getting...it sounds like a humpback whale...mmmooooooaoaaaaaa..it start and quickly builds in volume to the point the truck is almost shuddering and there is a squeal and I shut it down!

    what a terrible sound.
  4. phoebeisis

    phoebeisis Active Member 1000 Posts

    Big,
    I would be tempted to pull the oil filter off and cut it open to see if I find any metal.
    I think I would also drain the oil into a really claen container- let it sit so any shaving would drop out- pour the oil off and look for shavings.

    I'd do this because if you find shavings , you can just resign yourself to pulling the motor. Of course, you probably won't find shavings with a spun bearing, but the motor is still hurt.

    This stuff can drive you crazy. You didn't do anything to kill it; the rebuilder probably screwed up in some way. For $500 I would have taken that chance also; it was a good bet.

    If I had the $$, I would like to put the GM 383E stroker in to replace my 5.7 . It makes 90 hp more than a stocker would (340 vs 250hp).It is $4530 delivered with plugs, new dist,new plug wires,oil filter,installed plugs, gaskets etc). I'm certain GM performance must make a TBI drop in motor. Don't have $4500, if I did I would buy a 2002 for maybe $7000-$8000 which I sure don't have.

    Good luck with it. You can still part out the motor for decent $$.
    Charlie
  5. Big6ft6

    Big6ft6 New Member

    Thanks Charlie,

    I will do what you say to try to learn more. The noise sounds so terrible, it is hard to believe that running the engine for 15 minutes could have it this close to siezing. It has always had good oil pressure and had coolant for all of those minutes.

    I called the builder today even though I don't have any recourse with him since I didn't have the rebuild done, I thought I'd ask his advice. His first thought was that my torque converter (which is not bolted to the flywheel) was potentially rubbing on the flywheel, which I would think was a good bet if I hadn't already checked that, and if the noise was a little less horrible sounding.

    but let me tell you, the noise IS horrible sounding, it is a deep heavy moan, way too deep and heavy to be the flexplate brushing the mount pads on the torque converter.

    But I figured it was worth a shot, I will fill up the tranny with some fluid and bolt the torque converter up to eliminate and chance that the noise is from something in there rubbing, and give it another shot when I have a little more emotional stamina.

    Time for a weekend up north sitting in a tree.

    Any other ideas of what the deep moan could be, or advice, let me know, you all get me through the workday!
  6. CoolAirVw

    CoolAirVw New Member

    Did you have any luck??
  7. Big6ft6

    Big6ft6 New Member

    got a nice 8pt on my video camera, broadside at 15 yards. But it is "earn a buck" up here in Wisco so we're required to shoot a doe before we can shoot a buck, so I just was happy to get in on film.
  8. CoolBlueSS

    CoolBlueSS New Member

    What was your cooling problem? What does your top radiator hose look like when this noise is happening? I had one that a thermostat stuck closed causing the upper hose to be sucked flat. It made that same noise, and the pump was sucking air through the radiator cap.
  9. Big6ft6

    Big6ft6 New Member

    CoolBlues,

    Thanks for the idea, my thermo is operating properly as warm coolant is passing through the upper hose.

    this noise is a very heavy deep sound. It sounds just like I'd imagine an engine siezing would sounds like, or maybe a frieght train throwing on the brakes.

    Becuase of the magnitude of the sound I feel like two heavy peices of metal must be rubbing together very hard, and it gets louder very quickly. In my mind I picture a bearing surface spinngin and heating up, then getting bigger as it expands and jamming the operation of the engine.

    It doesn't make sense though. I have oil pressure and cold coolant...why would something in the engine start siezing? I just don't get it.

    Anybody ever had a bad problem with a distributor siezing up? The distributor spins freely when out of the truck, but maybe something bad is happening once it starts turning at running speed?

    But I can't imagine even a binding distributor being able to make the terrible sound that I hear. It sounds like a pistron siezing against the wall of a cylinder...yep...that bad. But I just can't figure why.
  10. CoolBlueSS

    CoolBlueSS New Member

    Only thin g I can think of is if you have an oil passage blocked after the oil sending unit. I would do like someone suggested, and cut the oil filter open to see what's in there.

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