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Hot Rods 327 Humming Me To Insanity

Discussion in 'The Hokey Ass Message Board' started by Scott Walter, Jan 6, 2018.

  1. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    Here's the whole bruschetta-

    Old build, 20+ years (literally as I was being birthed, so was this build), no miles before I got my hands on it.

    L76 327, 2.02 heads, unknown (pretty spiffy) cam, forged sluggies, long tubes, dual plane, 625 Street Demon, Roadrunner custom stall 12", built 350, 3.73, 31 10.50 drive tires

    Has the infamous pulsating vibration- has been process eliminated from the front dress, driveline, and tires. Balancer appears Ok, flexplate is correct and neutral balanced. New trans, and TQC, new shaft, and rear gears inspected.

    Here's the kick to the plums- a few years back (40k miles), I blew the tip of a pusher-rodder right clean off. She danced in the pan for a bit, but otherwise caused no damage, after pulling caps and whatnot. I was on a roadtrip in Seattle, and planned to just getter back on the flats with a pushrod and a rocker. I sourced one from Napa, but have a memory of there being a dispute on ratios.

    Therein lies my question; would a single rocker being of an unbalanced ratio (when relating to the rest of the squad) have the ability to cause a harmonic vibration?
    I know I know, I'm grabbing at straws- I get that. What else is a man to do when he has reached wits end other than grab for the short and curlies? Process of elimination is the only way
    Donuts & Peelouts likes this.
  2. Fat cams sometimes require different length push rods.
    I suppose 1 ODD ball pushrod and or rocker has a better chance of causing vibration issues than a full matched set would.
    Scott Walter likes this.
  3. s55mercury66
    Joined: Jul 6, 2009
    Posts: 4,061

    from SW Wyoming

    Just throwing this out there, is anything solid-mounted, engine, trans, body, exhaust?
    GlassThamesDoug likes this.
  4. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,476

    from phoenix

    Are U joint angles within a degree of each other front and rear?

  5. Hombre
    Joined: Aug 22, 2008
    Posts: 1,072


    Did this motor have the stock rocker arms, and push rods?
  6. sunbeam
    Joined: Oct 22, 2010
    Posts: 5,894


    Which push rod and how is the most likely way did the push rod end make it to the pan? If the motor 1.6 rockers and you replaced with a stock 1.5 it would be like a cam lobe being slightly down you usally don't notice that until there is quite a bit of wear.
    Last edited: Jan 7, 2018
  7. buffaloracer
    Joined: Aug 22, 2004
    Posts: 807

    from kansas

    I don't see that as being your problem. Check your lift at the valve to see if they are really different. Strong chance that they are not. I don't know exactly what you are trying to describe. Any chance that it is a lean surge?
  8. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,253


    You got it with zero miles and drove it for 40k miles before the pushrod replacement.
    Did it have the pulsating vibration during those 40k miles or only after the pushrod replacement?
    considering the overall cost so far (new trans etc...) I think I'd just put a new set of pushrods in and be done with it...physically and mentally!
    You already lost one thru failure anyway.
    Consider it preventative maintainance.

    You're sure its not just exhaust system harmonics you're hearing/feeling?
  9. dirty old man
    Joined: Feb 2, 2008
    Posts: 8,911

    dirty old man
    Member Emeritus

  10. driverquality
    Joined: Sep 17, 2017
    Posts: 22


    The most important questions to me are:
    -Is it engine speed or road speed related?
    -How fast of vibration is it?
    -Does it change when under various loads or sitting still in neutral?
    -On throttle/off throttle/maintaining speed any different?

    I’ve seen many driveshaft issues (balance, deflection due to length vs tube diameter, U-joints that look & feel good but replaced and problem gone, joint angle difference, etc) cause this, but have also seen engine balance, slight misfire, and tune issues be the culprit also.

    Sent from my iPhone using H.A.M.B.
    mad mikey and indyjps like this.
  11. slowmotion
    Joined: Nov 21, 2011
    Posts: 3,321


    Had a tight U-joint give a similar fit.
  12. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    Nothing solid, all three mounts just replaced, with zero change in occurrence, although they did seem to soften it from transferring through the body as bad
  13. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    I eliminated driveline, as it does it in both park and neautral.
  14. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    They are chromoly single piece rods, stamped (assuming stock) arms.
  15. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    Hmm, if the foggy mind serves me well enough, it was cylinder 3 intake. It appeared to be a sort of bit-by-bit type of deconstruction, as if it was chipping away against the rocker, vs simply breaking off; needless to say the pieces made their way down south to warmer climates.
  16. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    That will be the next action, if nothing else brings me some peace. It's seen many different fuel delivery devices, all with the same bzzzzzz-bzzzzzz-bzzzzzzz around 2500-3500
  17. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    I was fresh off the block, I didn't pay enough attention to her to actually say yes or no. The pushrod incident was about 65k ago, and I am only say for certain that I have been aware of the vibez for 45k.

    My intrigue on your question of exhaust harmonics is high- care to elaborate? I don't know enough about them to say yes or know

  18. lippy
    Joined: Sep 27, 2006
    Posts: 6,448

    from Ks

    I would maybe still be looking at the balancer. Lippy
  19. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    Damn. I just realized my detail on the actual problem was worthless.

    -Vibration begins above 2400 or so, and is very- harmonical?, strong enough to shake the jewels, but not enough to make the lady happy.

    -Absolutely RPM related, smooth as a Montucky Coldsnack when rolling freewheel

    -The level of load seems to advance its lady-pleasing-buzzing a bit, but not much. On de-cel, it's different but still present in that RPM

    -Ignition is new (x2), and timing has been double checked like a problem child

    -Driveline is new, tip to slippery tip

    kadillackid likes this.
  20. And So is that
    Joined: Jun 3, 2005
    Posts: 9,246


    I know you said the front engine dress was changed, but what exactly? As mentioned above, the dampener could be off a bit. OEM? New SFI style? Good used one (that may not be)? As far running and happening above 2400 RPM there's a bit of a "tell" right there. The rocker/push rod gig was coincidental but could be revealing symptom. This whole story would make me want to re-visit the timing chain and gears. I'm going to take it to heart that you're certain the flexplate is a true zero balance. But, since I went to that spot, nothing silly like 1 bolt is a little different in the convertor mounts, right? I'd rather speak in terms where you think of things based on input vs diagnostics by forum.

    I bought a Bronco dirt cheap once with the same maddening issue to the seller. Wrong flexplate. was a 460 "crate motor" from an auto parts store. Damn, I miss that thing...:(
  22. When you replaced the single pushrod and rocker have you went back to check it? If the deck or heads were milled flat it could warrant a custom length pushrod even with a stiff hydraulic cam.
  23. Mr48chev
    Joined: Dec 28, 2007
    Posts: 32,117


    You probably have but did you try it with the belts off to make sure that it isn't the fan or something belt driven making the vibration?
    little red 50 likes this.
  24. steinauge
    Joined: Feb 28, 2014
    Posts: 1,507

    from 1960

    I believe I would replace the harmonic damper on that engine.Some good,close up pictures of the engine,trans,mounts etc would be useful.
  25. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    Everything up front is new, beyond timing chain. Electric fans, so no issues with clutch or fan itself. OEM corvette style finned 8". I've clocked the converter and did check the bolts to make sure they were matching.

    Basically at this point, I feel like I've checked the fair majority of what is typical of harmonics, with zero change. Beyond letting her shimmy till she blows, I'm just checking all my bases.
  26. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    I've had the covers off, and everything appears skookum and kosher.
  27. Scott Walter
    Joined: Jan 6, 2018
    Posts: 17

    Scott Walter

    Running twin pullers, so nothing in the fan department. It's had many belts, two pumps, and two alternators. All, to no avail. Now that I'm actually thinking of it, I've never runer without the PS looped; I'll give it a shot this evening
  28. You say you feel it in park and neutral @ 2400 rpm.
    Run the engine up to 2400 and observe, make notes and such.
    Un bolt the converter and slide it back off the flex plate into the transmission.
    Start the engine and check for vibrations.
    This will tell you if it's engine related or Trans related vibrations.

    And when was the last time it had a good old fashioned tune up?
  29. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 5,971


    A harmonic vibration is caused by two out of balance things turning at slightly different speeds. The vrooom-vrooom-vrooom is caused by the vibrations being additive and cancelling repeatedly. It could also be exhaust noise and one thing out of balance. It sounds like you have checked most everything, but as suggested by a couple folks, I would remove all belts and also disconnect and push back the torque converter and run it up to 2400 or wherever the harmonic begins. Do you have an electric fuel pump? Pull the fuse on it. Heater or A/C fan? Turn it off. Twin puller fans will likely never run at exactly the same speed; consequently the noise they make would have a harmonic element to it, but it wouldn't be related to engine speed. Any play in the distributor shaft bearing?Good luck, sometimes these issues are real bastards to solve.
    Scott Walter likes this.
  30. Maybe place your question on a late model website???and your profile page is rather skimpy

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