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timing not staying in tune - suggestions?

Discussion in 'The Garage' started by loudnowlouder, Jul 16, 2002.

  1. loudnowlouder

    loudnowlouder 1/2 ton status

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    i've had a bit of a problem recently, my timing absolutely will not stay in tune, at first it would go out every 5-6 months, but its gotten very bad recently and wont stay in tune over night...
    i'm completely clueless at this point...

    so here's what i've done...
    checked the compression, perfect.
    checked for any vacuum leaks...none, vacuum is perfect.
    checked the carb, float bowls are perfect, but it keeps going from rich to lean due to the timing..
    replaced the entire distributor with a known working gm hei, same exact dist as mine, took it off of a perfectly running truck...
    put it in, ran great for a few minutes, shut it off, turned it back on, drove it maybe a tenth of a mile, got real hot, so i shut it off, timing was already out of wack, turned over 3-4 times before shutting off..
    i'm getting perfect fuel pressure, even took the carb off and took it partially apart, perfect inside, no dirt or clogs, etc...

    what really has me stumped is that its all brand new gm stuff, i have a 350ho deluxe with maybe 2000 miles on it tops....
    its got a new holley 4160 carb, new carter mechanical fuel pump, new gm hei...

    is there anything i'm missing?
    it will not drive because of this problem, never seen anything like this, i've never had the engine open, but there are no knocks or anything out of the ordinary...
    it normally overheats when the timing goes out, pretty sure its timing causing overheating, not the other way...the entire coolant system is new as well, water pump, radiator, hoses, heater core, it's definately all working, once the engine reaches the right temp the thermostat opens up, so its not stuck either....

    any thoughts would be greatly appreciated

    --adam herbert
     
  2. Wally81k5

    Wally81k5 1/2 ton status

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    I had similar symptoms before. And what it was, was that the cam was worn out. Who ever had it before me tightened the rocker arms too much and wore the cam out. So when i went to time it, i set it and it ran like a bag, it also changed on me. Just a thought..
     
  3. NoSmog73

    NoSmog73 1/2 ton status

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    Just a thought what about the bolt that holds the dis. down If it is lose the timing can move on ya.. Mine would move after I added a new intake the bolt wouldn't stay tight and I had to tighten it to the point of thinking It was stripped and then it held...mike
     
  4. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    What do you mean by "350ho deluxe"? Is this a new GM crate motor? It really sounds like the only thing left is the timing chain. I know that's not likely based on the low mileage motor but there just not much left. If this is a rebuilt motor, what brand of chain is it? Is it good quality stuff?

    Good luck...
     
  5. loudnowlouder

    loudnowlouder 1/2 ton status

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    sorry should have clarified, 350ho deluxe is the 330hp crate motor from GM, but it comes complete from oilpan to air filter, came with the carb & hei already installed, as well as the timing chain, harmonic balancer, and water pump...
    hehe i got it so i wouldnt have problems like this, i paid a lot for the factory reliability, but i'm starting to question it..

    i thought it could be the timing chain or cam, and if it is i'll be real mad, the one year parts only warranty is over, and if its the case i'll never buy a gm crate engine again...

    i even took the time to torque the dist bolt down, and it doesnt look like its moving at all, it'll start up fine one day, the next it wont start at all, thats a lot of movement considering it hasnt moved more than a mile in the past month....

    thanks for the suggestions!
     
  6. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    Man, I stumped...

    Do you have any ignition electronics? I have an MSD 6AL box on mine, it will do really wierd stuff and run extremelly bad if the alternator or battery has a problem. I've never experienced the overheating symptoms like you though. Just a thought...
     
  7. kennyw

    kennyw N9PHW Premium Member

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    I would paint a line on the base of the distributor going to the intake manifold and make sure that it is not turning. With everything so new it doesnt make sense to me.
     
  8. HarryH3

    HarryH3 1 ton status Author

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    Have you actually put a timing light on it to determine what's going on? I didn't see anything in your post about the amount of difference that you're seeing.
     
  9. Philly87

    Philly87 1/2 ton status

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    Does this motor come with a hyd. roller cam. If so have you checked to make sure that the cam is not walking. Roller cams require a retainer plate that bolts to the front of newer blocks or a cam button. You may also want to make sure the timing chain cover is not flexing and causing the cam to walk. Good point on the MSD too. If you are using an MSD box make sure you are using the cheapest standard timing light you can find. Any lights that are digital or have a dial on the back to check total advance will pick up interference and give you a false timing reading. Just a couple thoughts.

    Phil
     
  10. loudnowlouder

    loudnowlouder 1/2 ton status

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    thanks again for the replies guys...
    i dont have an msd box, so that cant be the problem...and its not a roller motor either...
    i actually started using a cheap timing light but when it kept going out of tune i bought a real nice digital one, unfortunately it didnt help out much...

    i've been putting a light on it a lot recently, and it can vary up to 6-7 degrees in a matter of hours, i can tune it so it runs perfect, and a few hours later it either wont start or wont shut down due to the timing being way off...

    i'm going to put a mark on the cap and manifold today to see if it is just the bolt, which would be great if its just that...but after all the time i've put into it i kinda doubt it...
    i guess at this point i have to assume its either the cam or timing chain with premature wear....

    thanks again
     
  11. muddin4fun

    muddin4fun 3/4 ton status

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    tighten the bolt /forums/images/icons/grin.gif

    Are you using one of those funky bent wrenches for distributors?
     
  12. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    I guess it's always possible that the dist hold down bolt is a little too long, maybe change to a stud / nut combo. That would solve any question of the bolt bottoming out.

    FYI - I'm bad about over tightening stuff so I (of course) killed the threads on my intake, I bought a stud kit, lock tight and a dist wrench - no torquing problems since.
     
  13. Hoover87

    Hoover87 Registered Member

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    Did you ever solve your problem? I'm having a few issues of my own with a 350ho.
     
  14. pvfjr

    pvfjr 1/2 ton status

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    I've been having trouble getting my dist to stay tight, pretty much the same symptoms you have. I even bought a new clamp and changed to a stud/nut combo. I can still tighten the CRAP out of it, but it barely tightens down the dist. I can still turn the dist if I try hard enough. I was just going to worry about it when I got a new intake. Until then, I'm just keeping an eye on it. I did think about putting a shim of some sort under the clamp, or bending the clamp to get it to put more pressure on the dist.
     
  15. dremu

    dremu Officious Thread Derailer Premium Member

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    I had to bend the clamp somewhat ... IIRC it took some fiddling to decide the best way to clamp it to get the most coverage. Granted mine is 30+ years old, but it was still strong ... just needed a little bending.

    Also be sure to stick it ALL the way down onto the dizzie neck; even a fraction of an inch makes a difference.

    Mine got to the point where I could move the dizzie by hand when the bolt was so tight I thought it would pop ... which was when I fiddled with bending it, and after three or four tries ... voila. Rock solid timing.

    I hate dizzies :D

    -- A
     
  16. Blue85

    Blue85 Troll Premium Member

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    Does the mechanical advance snap back when you turn the rotor by hand? It could be the mechanical advance sticking. It could also be a sticking vacuum advance. You could remove that and drive the truck. It's for economy while cruising, but it's OK to drive without.
     
  17. dheavychevy38

    dheavychevy38 1/2 ton status Premium Member

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    I have had the reluctor wheel come unpressed from the distributer shaft before.
     

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