very bad engine noise quiz

Discussion in 'Homesteading Questions' started by JV, Dec 6, 2004.

  1. JV

    JV Well-Known Member

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    Hello, I have a 1985 Nissan PU, 4 cyl, carburated engine. Over the weekend a noise started from the engine area and I don't know what it is. It started rather suddenly and immediately with it came alot more vibration and a small loss of power. The noise is a metal on metal knocking- it is at it's worst when you are just getting going and right after you shift gears. The noise gets faster as you increase the RPM's. Higher RPM's seem to diminish the loudness of the noise as well as the vibration. You can get the noise in neutral but you have to give the engine a real good amount of gas really quick. It does seem to be idling a little rougher but I am not sure. There is alot of vibration. even in neutral when it is idling and no harsh noises are coming from the engine, The cab shakes and so does the stick shift. I took each spark plug wire off, one at a time, trying to see if there was any difference in the noise when I revved it and there wasn't. I also disconnected the alternator belt to see if it was the water pump making noise and that made no difference. As you can see I am stabbing in the dark. Any help at all is highly appreciated.
     
  2. John Hill

    John Hill Grand Master

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    I think this is a noise that should be investigated immediately, metal on metal that you can hear while driving can be some things that are rather traumatic. It could be a crank or big end bearing or a number of other things. None will get better by themselves.
     

  3. ed/IL

    ed/IL Well-Known Member

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    Timing chain or belt is my guess.
     
  4. seedspreader

    seedspreader AFKA ZealYouthGuy

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    This might get a better response down in the Shop Talk forum, but my bet is it's a rod knock. An old trick my father taught me, if you have a broom handle that you can use that is sawn off flat on one end. You can place it against the block in several areas and put your ear to it and hear the local noise of the engine more distinctly, especially knocks etc.
     
  5. fordy

    fordy Well-Known Member

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    .................Common sense Rule Numero Uno (1)...Loud noises from the engine compartment should tell the owner to immediately Turn the Motor Off as soon as practical :rolleyes: . Unless , it's under warranty , then you can drive it until it explodes and hope the dealer will fix at their expense . Don't...drive your vehicle until the problem has been diagnosed !!...fordy... :eek:
     
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  6. Tracy Rimmer

    Tracy Rimmer CF, Classroom & Books Mod Supporter

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    Sounds like you've thrown a rod... at least, that's the noise two of my vehicles which did this made....

    Tracy
     
  7. JV

    JV Well-Known Member

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    I am relatively new to fixing auto's so what does throw a rod mean? What can you do about it? Is it the same as a rod knock? With the broom handle will I be looking for the location of the knock? That would be hard because the knock is really only loud when moving or in idle when I really juice the gas for a second or two.
     
  8. seedspreader

    seedspreader AFKA ZealYouthGuy

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    With the broomstick trick you should be able to hear it even at low rpm when you don't normally "hear" it. A rod is a connecting rod that connects your piston head to your crank. It typically makes a "slapping" noise if you have a rod loose from the head, a bad bearing at the crank is typically a deeper more menacing noise, both are major issues though and the broomstick may only help you hear the noise at the low end of the rpm range, so hopefully you don't "throw" a rod which is a complete breaking away of some portion of the connecting rod and usually results in a nasty hole in the side of ones engine block, and it's dangerous too. I threw a rod once on a four wheel drive going down the highway (no warning sounds before hand) and the shrapnel from the block blew out my front tire, glad I wasn't standing next to it "revving it" at that point.
     
  9. John Hill

    John Hill Grand Master

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    A big end bearing (i.e. rod bearing) really gets loudest when power is on. Try to start the vehicle moving by selecting a higher gear than usual, 2nd I assume. There will be a quite loud knock as you pull away if the rod bearing is run. You mentioned a big increase in vibration, this is not so noticeable with a rod bearing.

    It may be a valve or piston break up, take out each spark plug and look for one that is different to the others. If the end of the plug has been damaged by bits of metal hitting it that could be a piece of broken pistion or ring.

    You said there is only a slight loss of power, problems with piston, rings or valves would cause a fairly noticeable drop in power. A failed rod bearing will cause only a slight drop due to the reduced compression ratio.

    Use the broom handle to at lease determine if the noise is at the top or the bottom of the engine.

    There is a very slight chance that your problems are actual trivial (relatively) caused by a broken engine mounting. Does the clutch feel strange when starting from standstill?

    Driving without knowing what is wrong is really risky, if the rod bearing is indeed run you are causing damage to the crankshaft, if the connecting rod eventually breaks under the strain it may destroy the engine beyond practical repair. Ditto for a failing piston.
     
  10. fordy

    fordy Well-Known Member

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    .......................All youse guys that understand the basic interpersonal relationships betwixt and between the mechanical parts of a car didn't read the post that said basically JV Doesn't speak that lingo . Please don't think I'm being mean JV but telling you about connecting Rods , etc . is a complete waste of Your time . Best thing is to simply take it to a mechanic and ask them to diagnose the problem and how Much it will cost to Fix . ...fordy... :)
     
  11. Shygal

    Shygal Unreality star Supporter

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    Sounds like a rod to me, and thats pretty expensive :(

    But you MIGHT wanna check your oil too, sometimes when its low you can get a noise and you might be lucky and thats all it is.
     
  12. SouthernThunder

    SouthernThunder Well-Known Member

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    It can be any billion combination of things.. I doubt very seriously you have thrown a rod as you would have seen things get real bad real fast (within a couple of seconds) and then the engine would no longer run. When ya throw a rod you loose the piston and this tends to cause a huge calamity especialy in a small engine. It cuts cams, cylinder walls, and everything else without the piston to guide it so if this happened you would know it. :D

    It is likely a bearing has gone bad and spun out of its seat allowing the rod to knock. You could also have a hole in a piston, busted piston skirt, busted piston ring(s).

    Sometimes the tranny bellhousing bolts will back out and the case will slap the block and produce a knock. So will a cracked case.

    A broken accessory bracket can produce a knock. An exhaust manifold crack or leak can also sound similar to a knock. Head gasket gone bad leaking water into the combustion chamber will knock. Arching spark plug wires zapping a ground source will knock. Bad water pump will knock like crazy. So will a smog pump and any holes in the large tubes connected to it. Like I said.. theres a billion different things.

    I second the idea of hunting the noise down with a broom stick or cardboard tube. First place I would check would be the oil pan. :waa: Did you look at the oil yet?
     
  13. rambler

    rambler Well-Known Member Supporter

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    Mark me down for a timing chain.

    Some of the things people have mentioned can't be the problem - your engine would be smoking or in pieces when you punch the accelorator.

    But you could _easily_ be headed there. Take it to a mechanic.now. One of us is right here in this list, and the problem will get worse - and fatal to the engine. Perhaps dramatically so.

    A mechanic can take 5 minutes to listen to it, & will know what it is, and if it needs to be shut down _now_, or if you can drive it a week or 2 yet.

    I would _not_ risk driving it or bothering listening to it - have it looked at.

    Please let us know what turns up.

    --->Paul
     
  14. insanity

    insanity Well-Known Member

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    With the broom stick or long screw driver you will hear things you cant hear normally.But if you dont no what its supposed to sound like all you can do is tell where it is top or bottom of the block,or in the head.I bought a steth-a-scope (kinda like doctors use) from Auto Zone for this.One of the best tools ive bought.

    Yep could be a number of things.To many to guess accurately.
    But heres my guess anyway. When is the last time you put gas in it? Bad gas/water? Spark knock?
    You said it started suddenly.Where you reving the engine? A collapsed lifter makes a heck of a racket.Although more of a metal ticking sound than a knock.
    Been there learned not to rev an idling engine not under load the hard way. :eek: Also have spun crank bearings under high rpms.Rod knock.
     
  15. Quint

    Quint Well-Known Member

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    I hear that. I was out mudding in my truck once and was standing on the throttle and had a catastrophic engine failure. The crank disintegrated and blew the oil pan apart, shot 3 rods through the side of the block, broke both cylinder heads and then to add insult to injury the engine compartment caught fire. Made me a believer in carrying a fire extinguisher. It was spectacular from the cab and even more so watching it from outside I was told.

    As they say: If you must fail, fail magnificently.

    The sound could be about anything I would have it looked at immediately. I had a loose power steering bracket that was making a sound that was absolutely identical to rod knock. The mechanics I had look at it thought it was too until we started looking really really close at the belt tensioner jumping around.
     
  16. JV

    JV Well-Known Member

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    Thanks alot for all the replies, they have been very helpful. I would like to bring this to a mechanic but I live 10 miles from the closest one and there is a hill in the way that I don't think the truck would make it up. This truck is old, was only bought for $400, and really the body isn't worth putting anything over a couple of hundred bucks into at max. And since it isn't my primary vehicle I am going to see what I can figure out myself and maybe get a neighbor to look at. I an going to try to pinpoint where the noise is coming from, take off the valve cover to see if anything looks strange in there, and take out the spark plugs to see if one looks really bad. At least I will learn something. I did forget to mention that this problem first came about when I was 100 miles from home and I did manage to get her home at 35mph, so I don't think it has thrown a rod. Thanks again for the replies and I will probably have more questions in the next day or two.