Engine rattle under acceleration

Discussion in 'Small Block Tech' started by JN_Skylark, Dec 25, 2020.

  1. JN_Skylark

    JN_Skylark Well-Known Member

    Hey all,

    I've been working on adjusting the timing on my car, and with my first couple adjustments I've been getting a rattling noise under acceleration but I'm not sure if it's spark knock or not. Larry has been helping me with the process but I wanted to see what you guys think.

    The car is a 1969 Buick Skylark with a 350 4 barrel, the distributor is not original to the car (1112037, 1971?) and looks to have a recurve kit installed already. I don't have a dial back timing light unfortunately but I have one on order.

    Here's a clip that has the rattling sound under acceleration:
     
  2. Max Damage

    Max Damage I'm Working on it!

    That definitely sounds like valve clatter. If you are accelerating when that happens the timing is too far advanced or you are using poor fuel.

    This can cause damage!
     
  3. JN_Skylark

    JN_Skylark Well-Known Member

    I've backed off the timing to 0*, which is what the factory spec is. I am using premium fuel with a lead substitute so I don't think the issue is with fuel. But with the distributor being non-original to the car I'd potentially be losing performance with the curve being set differently, right? Another thing that worries me is that I sometimes get this rattle noise pulling a big hill even with the timing set to 0*. Could this again be cause by the curve being different?
     
  4. johnriv67

    johnriv67 Well-Known Member

    My guess is that your balancer slipped. Get cylinder #1 to top dead center based on looking down the spark plug hole, maybe even use a piston stop. Verify that you are at or close to 0* on the harmonic balancer, and the distributor rotor is facing directly at cylinder 1 or 6 under the rotor cap.
     
    Quick Buick likes this.
  5. Quick Buick

    Quick Buick Arlington Wa

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  6. Jim Nichols

    Jim Nichols Well-Known Member

    Try plugging your vacuum advance hose. You need a can with no more than 10-12. Stiffer advance springs may help too. On a 67 Firebird 400 I had, I ran 12 static with the medium advance springs. Also if you have high compression and the cam is advanced you could retard it if you have the multiple keyways.
     
  7. Quick Buick

    Quick Buick Arlington Wa

    Good point....
     
  8. JN_Skylark

    JN_Skylark Well-Known Member

    I read through Larry's guide of power timing, but unfortunately I don't have a dial back timing light so I followed the instructions of making a 30* mark on the balancer since I only have a conventional timing light.
     
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  9. LARRY70GS

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

    I think you definitely need to check the balancer for slippage. If that isn't right, nothing you measure will be accurate.
     
  10. JN_Skylark

    JN_Skylark Well-Known Member

    Will do, if the balancer has indeed slipped what would be the course of action?
     
  11. Quick Buick

    Quick Buick Arlington Wa

    Re Read Larry's post you dont need a dial back....
    Taken from Larry's post
    To do this with a conventional timing light, you need to make a 30* mark on your balancer. The Buick 350, and 455 balancers are 6 3/4" in diameter. Circumference (360*) of a circle is pi(3.14) X diameter. 6.75 X 3.14 = 21.195"/12 = 1.76" (30*). Looking at the engine from the front, measure exactly 1 3/4" clockwise around the balancer, and make a second mark. This is your 30* mark. Connect up your timing light, and watch your 30* mark as you increase the RPM's. At some point, your 30* mark will stop rising, and move no higher. This is the RPM, where all of your mechanical advance is in.
     
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  12. Quick Buick

    Quick Buick Arlington Wa

    Get it rebuilt.... Dont bother with a 50 year old used one..
     
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  13. BuickV8Mike

    BuickV8Mike SD Buick Fan

    How long have you had the car? Sounds like it was better before messing with it? ;)
     
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  14. LARRY70GS

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

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  15. JN_Skylark

    JN_Skylark Well-Known Member

    Less than a year, I picked it up in February. I must enjoy tinkering too much, I love fiddling with this car :)
     
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  16. JN_Skylark

    JN_Skylark Well-Known Member

    I did follow his instructions with the mark, but maybe I simply measured the mark incorrectly. I figured if I'm going further in depth with the timing it would be a good investment for future projects.
     
  17. Quick Buick

    Quick Buick Arlington Wa

    Hint==== use masking tape,,, cut that at 1.75'' stick it on the HB mark your mark. also put on both sides of the line.. ( just because ) dont ask...:oops:
     
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  18. BuickV8Mike

    BuickV8Mike SD Buick Fan

    Don't buy parts or make repairs yet. Timing is the key. I used the 30* degree mark method also. Recurving my distributor was my best investment to date. Have fun.
     
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  19. JN_Skylark

    JN_Skylark Well-Known Member

    I'll first check to see if the balancer is still true, then go from there.
     
    Max Damage likes this.
  20. mikethegoon

    mikethegoon Well-Known Member

    My 68 motor runs per °0 TDC- by the book. But it has new double roller new drive gear on cam and rebuilt distributer with new gear installed on top of all that. Had shop throw new cover on it. But they told me dist vacuum was bad.They set timing where they wanted too * then when it rattled they set it where I told them to.
     

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