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blazer started knocken; but only when cold ¿¿¿

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Muddin_Mavric, Mar 25, 2003.

  1. Muddin_Mavric

    Muddin_Mavric Registered Member

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    its a 83 blazer with a 305 and 33s

    I reaplaced the thrmo vac. swith that is right above the thermostate and then took it out in a friends muddy field. 2 days later when i started it agian it was fine till it started to warm up ( it seems to be about the time the joke starts to pull off) a bit and then when ever i would even step on the gas more that just a little tiny bit it started knocking. with my windows up it sounds like an exhaust leak sort of but when i roll down my window it sounds like a diesel /forums/images/graemlins/frown.gif when i gets up to about 150 deg. it stops. then today i noticed that sometimes from a stop( not very offten) if i hit the gas about half way but really fast it will knock a couple of times too but not as loud.

    my oil pres. gauge is off and only reads 7 psi but when it read that in the fall we hooked up a manual gauge and it read 40 psi so that should not be the poblem.

    i know that my flappy in the airintake that is sapose to let in hot air is not working i dont know if that could be making it run to lean or somthing.


    thanks for any help you guys can give me


    Justin Behr /forums/images/graemlins/k5.gif
     
  2. AK-5GUY

    AK-5GUY Registered Member

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    Mine knocks, and it needs a new engine. Bad rod bearing. Yours may or may not be the same. /forums/images/graemlins/confused.gif If it is, don't run it anymore, because you can get a good rebuild shop to knock about 300 off the price of a rebuild if you save the block and dont crack it from blowing the main. Dont know if it is?? but trying to help! /forums/images/graemlins/grin.gif
    Harrison
     
  3. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    It's piston slap or a main bearing. Either one usually just gets worse until it fails or you replace it. Mine started doing this on a cold start up and progressed to where is sounded like a desiel at idle. This is when I pulled the engine. It did take a year to get really bad. Just at some point you might not trust taking it on longer trips. Good luck.

    Mike
     
  4. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Sounds too damn intermittent for the rotating assembly. Get it hooked to a manual gauge immediately and see what the real story is. Generally, with a bad rod it will knock when its wamred up. Your oil is thinner and lets in a little more clearance. Then once its warm and out of gear, start feathering in the throttle and it should start to sound like the three stooges (you know, nyuk nyuk nyuk). Then you'll get to a point when its wound up enough that the knock will disappear. Pretty much classic rod knock if you can get it to do that.

    Bad mains will usually just knock like crazy right from the start, but thats rare. The only way to kill a good working main is to starve it for oil, get crud in it, or heat it up.

    Change your oil into a clean bucket and go prospecting. If you see silver and copper colored flakes, thats the end of that /forums/images/graemlins/tongue.gif

    Could just be good old fashioned spark knock. Check your timing, don't buy crap gas, and maybe throw a little sea foam in there to clean things out. 1/3 in the tank, 1/3 in the crankcase before and oil change, and 1/3 right down the carb while its running. /forums/images/graemlins/wink.gif
     
  5. AK-5GUY

    AK-5GUY Registered Member

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    Oh, yeah, almost forgot, if it is a bad main, you will definitely know. It will knock all of the time and is very very loud. Mine rattled the whole truck, and my brother, who was 2 cars back in a new suburban, could hear it over the radio! Just though I would let you know.
    Harrison
     
  6. Muddin_Mavric

    Muddin_Mavric Registered Member

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    Thanks for all the replys i think i will check into the spark knock and the seafoam idea first. it sounds the cheapest /forums/images/graemlins/smile.gif

    since its a 305 i dont think i will be rebuilding it so ill just run it till it blows.

    to me it just doesnt seem possible that somthing mechanicaly inside could be wrong the way its not there till it warms up a little but then goes away once fully warm. well as warm as it gets. /forums/images/graemlins/confused.gif
     
  7. Muddin_Mavric

    Muddin_Mavric Registered Member

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    ok i got the flappy in the intake fixed so now it will suck in warmer air but after it was warmed up if i hit the gas real quick it still knock for about the first 3 cylinders that fired.

    today when i left school and it was about 65 deg. out it never knock at all well except for the above mentiond condition.

    if you guys could let me know wich way i need to turn my distributer to retard the timing a bit that would be great. i think its counter clockwise when viewed from above??


    thanks for all the help.


    Justin Behr /forums/images/graemlins/k5.gif
     
  8. bryguy00b

    bryguy00b 3/4 ton status

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    i know this is nothing to do with it kind of..BUT..speaking of knocking..i am rebiulding a small 5 hp engine form a minibike that started knocking something wickid this winter. i just went to start it up and it knocked so loud. i took it all part and found nothing wrong visualy. any one sure what it is? im about ot but it back together with just new rings and gaskets..
     
  9. Muddin_Mavric

    Muddin_Mavric Registered Member

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    well on my way to school today it started to knock just a little after its warmed up /forums/images/graemlins/shocked.gif and after i pulled out on the highway before it was warmed up it started knockin as usual in OD but i shifted it to D with out moveing the gase pedal and it went away but if i step on the gas harder it will come back.

    coule me fixing the flappy in the air intake do that? i still want to try and retard my timing as soon as i figure out wich way to turn the dist.


    if that dont help i will go prospecting in the dirty oil.



    justin behr /forums/images/graemlins/k5.gif
     
  10. TxK5Blazer

    TxK5Blazer 1/2 ton status

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    I say junk the 305 and find you a 350 that is what I had to do I burned up the first one the same night I blew up the tranny. /forums/images/graemlins/usaflag.gif /forums/images/graemlins/k5.gif /forums/images/graemlins/usaflag.gif /forums/images/graemlins/pimp1.gif
     
  11. bajaviking

    bajaviking 1/2 ton status

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    You need to turn it with the clock to retard it, give it a few degrees and then drive it. If it continues knocking give it a few degrees more.
     
  12. BRN78BLAZER

    BRN78BLAZER 1/2 ton status

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    any chance this could be lifter noise?
     
  13. Muddin_Mavric

    Muddin_Mavric Registered Member

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    i have no idea. but with my window rolled down it sounds like a diesel. with my window up it just sounds strang.
     
  14. chiefKP

    chiefKP Registered Member

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    My 84 K5 with a 305 did the same thing. I discovered - after chasing down a different problem - that rings on 3 of the pistons were broken. No matter what I did...timing adjustments, adjustable vacuum (sp?) advance, EGR or not, it did the same thing. It ran okay, though. Not great. Just okay.

    Try a detailed compression check. You may finnd that your compression is not what it should be.
     
  15. Muddin_Mavric

    Muddin_Mavric Registered Member

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    well i retarded my timming and it helped alot. before there was about a 2 to 4 minute period of time where it would knock know its down to about 20 seconds.

    but now the thing has no power at all past about 1/3 thorotle. this thing is such a POS! and when i put it to the floor it has even less power. the engine still winds up.

    it use to do this before but it would come and go. but it would come on like the flick of swich and then go away later.



    /forums/images/graemlins/k5.gif
     
  16. Muddin_Mavric

    Muddin_Mavric Registered Member

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    well i finally found the problem after i had my uncle check my timing wich was with in 2 degreas of where it should be.

    he lent me a book he has and i was reading in there about how aparantly my blazer has a brain hooked to the distributer that should retard the timing when it senses its knocking but obviously that was not working. and the vac hoses are wired so that when its cold it get full vac. advance.

    i rewired the vac lines and now it doest run quit as good when its cold but it does not knock /forums/images/graemlins/cool.gif

    after i found out my blazer has a brain i serched on here and from what i read its a good idea to unhook it and since it dont work right anyways i think i will do that this week end.


    Justin Behr /forums/images/graemlins/k5.gif
     

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