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CRAP! (Punch the wall and break knuckles) motor has a knock

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazer_Boy, Jun 17, 2001.

  1. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    No I haven't been declared DOA (if you're wondering where I am), I've been out at my uncle's doing a resto on my '82 and changed the head gaskets on my dad's '89 Jimmy which brings to my question. The gasket blew on the 7 cylinder and when I changed the oil after the gasket change, about a gallon of coolant came out before the oil (truck sat a month before I tore it apart). I put two oil changes through it, fine tune everything down to a gnat's a$$ (rocker arms too), drove for a few days and just took it home .

    On the way home when I started to slow down for lights I started to hear a knocking noise like someone knocking their knuckles on wood. I figured maybe the rotors needed turned and some brakes. So I stopped on a side street and dropped it in neutral. A knock at idle and leaves after you rev it slighty. It only seems to knock and very low RPMS. So I put it in gear again and got on it, has TONS of guts still (more than when we bought it). I checked the oil and it is super clean and it does have pressure. My uncle thinks I could have a bad exhaust gasket, something is messed up on the fan, or something minor (he hasn't heard it, I called and asked.) I think the bearings are toast because it was sitting with an oil pan full of coolant for a few weeks. Anybody have any ideas.

    <A target="_blank" HREF=http://www.geocities.com/bigkern76>http://www.geocities.com/bigkern76</A>
     
  2. wayne

    wayne 3/4 ton status

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    Usually when a bearing goes it will get louder when you rev the engine. I have had 3 engines that bearings went on and they did get louder with rpm's. Just my $.02.

    <A target="_blank" HREF=http://jamonline.homestead.com/fromthegroundupK54x4/89Jimmy.html>http://jamonline.homestead.com/fromthegroundupK54x4/89Jimmy.html</A>
    <font color=blue>Happy Trails<font color=blue>
    <font color=blue>Wayne<font color=blue>
     
  3. Seventy4Blazer

    Seventy4Blazer 3/4 ton status

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    leaves after a small rev... stickey lifter maybe?

    1974 Chevy Blazer Cheyanne. lots of plans for it....
    but it is on 33's now, with saggy old springs. i am in so cali if ya got any parts for me.
     
  4. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I gave the lifter valley a good cleaning and the heads were machined and cleaned in the hot tank so I know the top is OK. I started the motor and started crawling around under the truck in the street (in my good clothes, lol). The noise sounds like its comming from the middle of the pan towards the back. I'm willing to bet that the pump is on its way out or something got knocked out when I was dropping the distributor in. The thing only runs 16 psi for oil pressure at idle when its warm. The knock is pretty meaty sounding but doesn't have as violent of a sound as a rod. Its sorta of a shame this happened because I cleaned the truck for 4 hours and was going to suprise my dad for fathers day cause it runs like a bat outta hell and he hasnt drove it on over a month.

    <A target="_blank" HREF=http://www.geocities.com/bigkern76>http://www.geocities.com/bigkern76</A>
     
  5. yeild2me

    yeild2me 1/2 ton status

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    man, the same thing happened to me a few years back. i pulled into my dads driveway, and heard this killer knock, and got that "not so good feeling" in my stomach. i just knew the bottom end was knocking, but my dad (who is far from a mechanic) walked up with a wooden dow rod and was listening to the alternator, power steering pump, then finally the water pump- he tossed me the dow, and said "go buy yourself a new water pump". sure enough, it was the sorce of the knock. it wasnt leaking or anything, just knocking.

    make sure you check EVERYTHING first!!!!

    hope this helps........................rob

    AIRBORNE!!
     
  6. bandit

    bandit 1/2 ton status

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    id cheackever thing first and then think about your lifters mine had horrible knock in it sat for like a moonth waiting fora new tranny got it all started it up and jsut heard theis god alful knock i had collasped a lifter alothought it stayed the whole tiem the truck was runing idle or not y ou might have a stickey one or something

    AJ
    Soon to wheelin spot near you
    Project Harvey[​IMG]
     
  7. DMK

    DMK 1/2 ton status

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    My 66 389 pontiac was doing this at low speed and idle. As you reved the engine noise would go away. Went out to start car one day and it would not start. Bad fuel pump, changed pump no more noise. Also as mentioned water pump bearings, alternator bearings could also do this.
     
  8. Pugsley

    Pugsley 1/2 ton status

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    My old wonder-dually's 454 had a knock like that - after throwing a fit and cursing the day that I spent $1200 bucks on that POS engine, I came back out and went over it in a calm and rational manner - turned out that the water pump was kaput. $40 and an apology to the neighbors later, I was running knock free again.

    I'm so poor I can't even pay attention [​IMG]
    <A target="_blank" HREF=http://pugsley.alloffroad.com>http://pugsley.alloffroad.com</A>
     
  9. ken

    ken 1/2 ton status

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    Also, if you have an auto tranny, the flexplate (flywheel) likes to crack around the 6 bolts that holds it to the crankshaft. When they crack, they sound JUST LIKE a bad rod bearing/rod knock. Pull the inspection cover and shine a flashlight up there and see if you can see any cracks. I've had this happen to me about 3-4 times over the past 22 years on my GM 4x4s. A good upgrade is to get a heavy duty flexplate, they don't crack as easy. Good luck.

    ken
     
  10. GRINCH

    GRINCH 1/2 ton status

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    I agree with Ken, Check your flywheel. I had a friend with a Gran National that sounded like a rod was banging. Turned out to be the bolts on the torque converter were loose. Only takes a few minutes to pull the inspection cover.

    The Few, The Proud, The K5 Blazer
     

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