1988 Silverado K2500 won't start (Valves)

Discussion in 'GM Powertrain' started by daddytech, May 19, 2011.

  1. daddytech

    daddytech Epic Member 5+ Years 500 Posts

    I have a 1988 silverado k2500 4wd that i traded a computer for so that my son could have something to drive, I got it started as it shows here in this video on my You Tube channel


    I went out and adjusted the valves by turning the crank to top dead center then setting the valves to zero lash +1/2 turn both of the #1 cyl valves, then 2,5&7 intake and 3,4,8 exhaust. then i rolled the motor one full rotation which should have set the valves at cyl 6 then was told to adjust to zero lash + 1/2 turn on 3,4,6,8 intake and 2,5,6,7 exhaust

    when i attempted to start the truck after that it backfired through the throttle body and caught the whole top half of the motor on fire. where did i go wrong?
  2. stephan

    stephan Rockstar 4 Years 5000 Posts

    I think one or more of the intake valves are too tight & are not closing & when that cylinder(s) is firing, it is blowing back up the intake track & through the carb.
    Your adjustment sequence & the valves I & E. you adjusted per cylinder per 360 degree rotation, is all correct, so all I can think is that you could have been one rotation off to start with, or the 1/2 turn during a static adjustment was too much & is not allowing one or more valves to close. I would start over & double check that you're on #1, loosen them back up & set them at zero lash. Then procede to #6 repeat with that sequence. Then start it up, warm it to maximun operating temp & adjust them with it running. Back each one off till it clatters, then slowly tighten untill it just quiets, then your additional 1/2 turn preload.
    One other possibility since this truck is new to you, is that a valve could be burned & just not sealing. Did you do a compression check or a leak down test on this before you started the valve adjustment? No reason to do a comp check now untill you re-run the valves, just wondering why you started with a VA right off the bat?
  3. daddytech

    daddytech Epic Member 5+ Years 500 Posts

    Well actually the truck has 215,000 miles on it and while the timing chain is still tight the valves were what was keeping it from running in the first place, someone had cranked down on them so tight that there was no way you could start the thing. my neighbor was going to help me adjust them and had backed them off to the point they were all lose and it started up and ran, was a little rough but it ran. i tried adjusting them by using the specs i mentioned and now it just back fires throught the carb and tries to light the engine on fire so i am thinking you are right about the valves being too tight the way i was doing it before , going to try backing them all off to zero lash, start the truck and try at again with it running this time and see if that helps any. thanks! BTW
  4. stephan

    stephan Rockstar 4 Years 5000 Posts

    Roger that, if you had to loosen them before, but you were able to get it started, then I'm sure it'll work this time too. When they're too tight it just cuts the compression down to where the mixture will barely fire off. When you adjust them running, only pull one valve cover at a time cuz it will throw oil every where. You can also get the adjusting clips to cut down the oil spray on the side you're adjusting. You might ask your neighbor if he has a set of these. If he doesn't you can buy a set for about $10. & it'll be a well spent ten lol. If you've adjusted valves with the engine running before, you already know what I mean :)
  5. daddytech

    daddytech Epic Member 5+ Years 500 Posts

    never have adjusted them with it running the that may have been the mistake i made. instead of just adjusting them when it was running till they quit rattling i shut it off and did the zero lash adjustment. because of the weather i haven't had a chance to get back out there and do more with it again yet but i'll give that a try and that's a no on the question about had i run a compression or leak down test on it yet too. basically this is my first valve adjustment. the theory of the guy i got it from was that the timing chain was stretched or it could be the valves because they were cranked all the way down and it wouldn't even attempt to fire up. so yeah i'll back them off and try it again the way you described and this time maybe with only 1/4 of a turn after the zero lash and see if it makes any difference then if it fires up i'll do the running adjustment if it's needed.

    sounds like a plan and it's still a much better plan than what i was using before going to try just setting it to zero lash first again and see if it cranks up and go from there.

    Thanks for the help.
  6. daddytech

    daddytech Epic Member 5+ Years 500 Posts

    SUCCESS!! well kinda, I backed the valves all off to zero lash again and magically it started back up again. of course everything was rattling but there was no oil spashing out the top of the motor at all so i am thinking the oil pump is trashed or gone too.

    The MAJOR disappointment is now that the truck runs i find out there is at least one rod knocking. I wasn't sure that's what i was hearing the first time the truck was running but i know now after getting it cranked up and letting it run a bit that it's DEFFINATELY a rod so now i have to pull the motor and re-work the bottom end. as if i didn't have enough to do around here already, but knowing is half the batttle supposedly. I am betting who ever coined that phrase never worked on a motor before lol
    Last edited: May 30, 2011
  7. stephan

    stephan Rockstar 4 Years 5000 Posts

    I think you're right about the oil pump being shot. It either broke the shaft or the bypass valve in the pump is stuck open, or the pickup tube might have fallen off into the pan. I'd put a new pump on & try it before rebuilding the engine. The rod might just quiet down when it gets oil to it, same with the valve lifters & rockers.

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