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new cam, backfires thru intake

Discussion in 'The Garage' started by 89Burben, Mar 26, 2006.

  1. 89Burben

    89Burben Registered Member

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    i just installed a comp cam, with new lifters and whatnot in my tbi 454. I am in the break in procedure and the truck was running good when i first started it up, and after about 10 minutes of running, when holding the rpms steady at 2000 rpm, it would run smooth, then there would be a slight vibration for about 5 seconds then go back to smooth, almost like a plug wire grounding out, but i dont think it was that bad of a vibration to be on 7 cylinders.....

    the other problem is that you cannot rev the truck up abruptly or it will backfire through the intake somtimes. i have new plugs and wires. the distributor is fairly new along with the cap and rotor. the timing is set at base or zero. grounds seem ok and im getting enough fuel pressure. the heads were just redone.

    there seems to be a little valvetrain noise. when i adjusted the rockers they were adjusted when the lifters were not pumped up or filled with oil. they were new.

    I used the turning of the pushrod method then when there is a drag felt, crank the nut down 3/4 of a turn. do they need to be re-adjusted now that they are pumped up? thats all i can think of........

    thanks
    brian
     
  2. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    I would say yes, redo your valve lash now that the lifters are pumped up. I don't know if that is causing your problems though.
     
  3. AZ79K5Project

    AZ79K5Project 1/2 ton status

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    Check your timing.
     
  4. skelly1

    skelly1 1/2 ton status

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    valve lash
     
  5. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    ditto... :D
     
  6. JEBSR

    JEBSR 1/2 ton status

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    adjust those suckers
     
  7. 89Burben

    89Burben Registered Member

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    alrighty i adjusted them, and checked my timing which seems to be good. when i first started it up it sounded good. (no noises and no backfiring) after about i minute of running it you can now hear noise coming from the valve covers again but no backfiring. do they need to be re-adjusted??? or do i have a bad lifter???


    another problem that it seems to have is at a steady 2000 rpm it will intermittently drop about 100 rpms and the truck will shake a little, then go back to 2000 rpm and back and fourth.....the wires, cap, rotor are new...
     
  8. 89Burben

    89Burben Registered Member

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    well i just started it up again tonight and its not popping through the intake anymore i think that was a timing issue.

    i changed the oil for the first time and there was microscopic metal dust that looks somewhat like the mettallic that is added in automotive paint. i believe that there would be much more if a lobe on the cam was worn off.

    As far as my valvetrain noise problems go i have a distinct ticking coming from the passenger side bank of cylinders, that ticks about as fast as the timing flash on the timing gun.

    currently i have 87 inthe tank. i have new heads that yield about 9.2:1 compression.....should i be running a higher octane?? or is my problem with a lifter/lobe/or rocker....
     
  9. damewood

    damewood Registered Member

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    that almost sounds like a lobe wearing if it persists take your valve cover off and check your push rod travel u should be able to tell that way
     
  10. beater_k20

    beater_k20 Banned

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    normal break in of a cam will cause a slight metallic look to the oil, but you have to look REAL close. from what you described, that cam is junk.
     
  11. 1-ton

    1-ton 1/2 ton status Premium Member

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    I am thinking you adjusted your valves to tight, when you turned them 3/4 of a turn. That was too much for when the lifters filled with oil, which caused valves to hang open during the compression stroke. That is why it popped out the TBI. I have tried both pre-filling lifters before installing them, and installing them dry. It is really a matter of preference, but I have found I like installing them dry because I get a better feel for when the pushrod is seated against the lifters with my fingers. If the lifters are pre-filled, then the lifter tends bleed down when the pushrod is tightened down to it...making it hard to get a feel for the proper pushrod tension. When I adjust my valves...first, with the lifter on the low side of the cam lobe, I use the push rod spin method, just until I get enough drag on the push rod that I cannot spin them easily anymore with my fingers. Then I turn the rocker arm adjusting nut only 1/4 of a turn more, which allows enough slack for the lifters to pump up with oil. I may not prefer pre-oiling my lifters, but I am a big fan of pre-oiling the engine before its initial start. I am also a big fan of running valve adjustments on a Chevy engine, after I have completed initial fire up and a little break in time.
     
    Last edited: Apr 1, 2006
  12. 89Burben

    89Burben Registered Member

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    ok, i reved the truck up to higher rpms about 3000 and the ticking got faster and it popped a little thru the tbi...
     
  13. 89Burben

    89Burben Registered Member

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    i adjusted the valves when the lifters werent pumped up they were new. i also did use the twist between your fingers method, but i turned them down 3/4 of a turn according to the haynes method. i readjusted them yesturday and used the firing order method and turning the crank 90 degrees and cranked them down to 1/2 and this was after running the truck for a while.....so im assuming the lifters are pumped up.........should it be a 1/4 you are saying?? is this when the lifters are pumped up or not??
     
  14. RootBreaker

    RootBreaker 3/4 ton status Premium Member

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    my father has been a mechanic for 45+ years.. he just helped me do mine... now I dont know if a 454 is different....but I believe he even checked my chiltons manual and was like.. wow they tell you to do this too.....

    with #1 @ Top Dead Center - they tell you what valves to tighten... my father had me tighten them until there was 0 play... then loosen until you can move the pushrod.... then snug till play goes away.... then 4 x 1/4 turns..... yes 1/4 turn increments and 4 of them.... we did that last time we took my heads off and it was perfect then we did it this time and it is good again.....

    the manual then said I believe.... #6 @ TDC and which valves are left.....

    my truck just popped through the intake but that was timing was retarted real bad....... too low.... hope some of that info is useful if not.... sorry :crazy:
     
  15. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Are you running a proper TBI cam? If you have one particular 'tick' it can only be lobe, lifter, rod end damage, rocker/pivot ball, sticking valve, valve spring or valve seat problem.
    Find out which one is ticking. (put oil deflecter clips on the rockers if you can get them and run it with the cover off to listen to each one with a screwdriver to your ear). Then start at one end of the 'train' and use a process of illimination. Measure lobe lift, if that's good pull the rocker and check the push rod ends, rocker and pivot ball etc.
     
  16. 1-ton

    1-ton 1/2 ton status Premium Member

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    If you look at a factory GM shop manual, they will say turn the adjusting nut 1 full turn, but I guess a number of techs outside of GM felt this was too much, which is why you will see Haynes and Chiltons manuals list 3/4 turn instead.

    The whole Chevy valve adjustment topic, has always been a hotley debated subject. I have read entire articles in Car Craft and Muscle Car magazine devoted just to this subject of valve adjustments on a Chevy engine. A lot of experianced Chevy engine builders have developed their own favorite method for doing this (like I have). I feel sorry for any rookie that ever posts asking opinions on how to do this because you are going to get so many different answers, that you will be more confused after you read the opinions, then when you first started.
     
    Last edited: Mar 29, 2006
  17. big454blockchevy

    big454blockchevy Registered Member Premium Member

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    Hopefully it's not a bent valve .
     
  18. 89Burben

    89Burben Registered Member

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    well i took off the passenger side valve cover and took a long piece of wood and put it onto the rocker stud and listened. i found a few rockers to be loose. i adjusted them while it was running and to my supirze not alot of oil came out at all like i had imagined. From what other ppl were saying i was predicting a gizer, yet it was more liek a seeping outa the holes. anyways now that they were adjusted i shut the truck off to put on the valve cover and now the starter clicks when i key it :mad: ..........thanks to advanced auto:rolleyes:
     
  19. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    I'd be pulling that intake to peek at those cam lobes at this point...
     
  20. chevyk2500hd

    chevyk2500hd 1/2 ton status

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    When I did my 383 swap on the truck mine would also shot flames out the intake. After i added bigger injectors and a new custom chip the problem went away. I would be willing to say your buildup is alright and the computer just doesn't understand.
     

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