The honeymoon is over – Broken timing chain?

Discussion in 'Street/strip 400/430/455' started by accelr8, May 29, 2021.

  1. accelr8

    accelr8 Well-Known Member

    Well, I’m joking about the honeymoon being over. I’m still excited about the car, but it looks like I have a bit of work ahead of me. I’m pretty sure the timing chain broke.

    I’ll give an account of want occurred and I’d like to see if anyone has any ideas of what might have happened and any suggestions moving forward.

    It’s a ’72 Skylark with a 462. Mods are in my signature (per previous owner’s records). I bought the car about a month ago. It was in storage for at least 5 years, but possibly longer. Since the car was sitting so long, I only started it long enough to hear it run and make sure there were not any serious issues with the engine. I trailered the car home, changed the oil, topped off some other fluids, and then started it. It seemed to run fine other than a bad header gasket leak and some smoke coming from the valve cover breather.

    The next day I took it for a ride once the car warmed up. I jumped on it a few times and it seemed to run fine, other than the fact that it seemed considerably slower than I was expecting. It seemed like a high 13 sec. car rather than a low 12/high 11 sec. car. (There are low 12/high 11 sec. time slips in the previous owner’s records.) I drove it normal for maybe 5 – 10 minutes more until I got home. I pulled the car in the garage, put it in park, and before I could turn off the key the engine “coughed” and died. I tried to restart the car, but all it did was crank and throw a ton of gas out of the carb. I disconnected the electric fuel pump and let it sit for probably a week while I was working on other stuff on the car. Today, I poured some gas in the carb and cranked it. It cranked fine, but did not make any kind of noise that would indicate it was trying to start. I pulled the distributor cap and cranked it. The rotor did not move. I cranked it while looking through the valve cover oil fill hole. I could only see the front rocker of cylinder 1, but it did not move. I am not a mechanic by any stretch of the imagination, but it seems like a broken timing chain to me.

    My thought is, the first thing to do is a leak down test on each cylinder to try to determine if any valves are damaged and then start disassembling the front of the engine to check/replace the timing chain.

    Any thoughts on what happened, why at idle and not WOT, and any suggestions?

    Thanks!

    Jim
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    You can see the timing chain through the fuel pump opening. Being the car has an electric fuel pump, you probably have a block off plate, simple to remove. Have a look.
     
    69GS430/TKX and john.schaefer77 like this.
  3. Matt Knutson

    Matt Knutson Well-Known Member

    "Any thoughts on what happened, why at idle and not WOT, and any suggestions?"

    You got lucky - WOT usually comes with full damage
     
  4. accelr8

    accelr8 Well-Known Member

    Larry - Good call! I pulled the block off plate and I can see the chain, but it's just draped over the cam gear. I pushed on it and it just moves back and forth.

    Matt - That's typically not my luck, but I'll take it in this case.
     
    johnriv67 likes this.
  5. Mart

    Mart Gold level member

    Find the issue yet?
     
  6. DaWildcat

    DaWildcat Platinum Level Contributor

    Just a thought, pull the distributor and have a look at the gear, and shine a flashlight down into the front cover distributor hole to see how the camshaft's drive gear is doing. Excessive wear on either is not uncommon and can result in the distributor "jumping", losing original ignition timing.

    Devon
     
    Max Damage likes this.
  7. Mart

    Mart Gold level member

    This is puzzling.
     
  8. FLGS400

    FLGS400 Gold Level Contributor

    Maybe the roll pin in the distributor gear came out or broke?
     
    Max Damage likes this.
  9. accelr8

    accelr8 Well-Known Member

    It looks like a broken timing chain. I pulled the fuel pump block off plate and the chain is still draped over the cam gear, but when I push on it, it moves all over.

    So I guess the next few questions I have are:
    1) do I replace just the chain or the entire timing set?
    2) what size chain/set do I use? I looked on TA’s website and they have different size chains based on whether the block has been align honed. I don’t know much about the engine build, so I don’t know if it’s been align honed, and if it has been, by how much. I believe the block is bored to a 462.
    3) do I need to check the valves for damage? As Matt noted, I got lucky that the chain failed at ideal, but is it wise to check the valves anyway? I now realize my previous comment about a leak down test probably doesn’t make sense since I’m not sure how I can rotate the cam to close the valves. So if I should check them, is there another way to do so without pulling the heads?

    Thanks!
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    All you need to do to close ALL the valves is remove the rocker shafts, very simple, 4 bolts, and the shaft and rockers come off. Putting them back on, just torque the bolts to 25 ft. lbs.

    Then do a leak down test on each cylinder and see.
     
  11. sean Buick 76

    sean Buick 76 Buick Nut

    Just replace the whole timing set and I wouldn’t worry about the valves.
     
  12. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

  13. Super Bald Menace

    Super Bald Menace Frame off oil changes

    It's not the chain that is longer or shorter in those sets, its the gears that are different sizes to accommodate line boring
     
    PGSS and Mart like this.
  14. Stg'd 2Discover

    Stg'd 2Discover Lumpty, Lumpty, Lumpty

    I ran across this issue on a car many years ago and it was cam and distributor wear.
    I second Devon's suggestion to pull distributor first if rotor is not moving while cranking.

    Tom
     
    Max Damage likes this.
  15. pphil

    pphil Well-Known Member

    The pin sheered off the dist gear.....just my guess
    Pull the dist and see

    Scott
     
  16. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    That would not explain the #1 rocker not moving, just the distributor rotor.
     
    johnriv67, Smartin, FLGS400 and 6 others like this.
  17. accelr8

    accelr8 Well-Known Member

    Thanks for the links Larry, and for everyone else's comments! I think I'll do a leak down test just for my own peace of mind and order a timing chain set.
     
  18. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    You can save a little time if you pull the rockers and lay a straight edge across the valves. If they are all level you're probably good.
     
    chrisg and 69GS430/TKX like this.
  19. accelr8

    accelr8 Well-Known Member

    Thanks Joe!
     
  20. accelr8

    accelr8 Well-Known Member

    It looks like the bolt that holds on the cam gear walked off, the gear got loose, and the chain broke. The second cam gear bolt was barely on.

    IMG_E1285.JPG IMG_1284.JPG
     
    bobc455 likes this.

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