<VV> Weird clattering

[Daniel Monasterio]

Hi Bob,
     Took off plugs and all of them look ok. All show a light brown color on ceramic and dry black around. The sound is definitively like detonation (spark nock) . It is similar to the clattering when timing is too far advanced and/or using low octane gasoline but, it is less audible and with a higher pitch.  The noise dissapears instantly at deceleration. It is different from a bad lifter, scrapping or any other mechanical noise (well, it is actually mechanical but not produced by mechanical troubbles). The manometer doesn't show any abrupt change and oil pressure is steady around 35 psi (90º-100º ambient temps.). Usual head temps. are 300-350 with maximums of 400 (prolonged uphills).
     On the test with a shorted plug, do you mean driving it on 5 cylinders ?
There is no noise at any rpm with the gearbox in neutral. One more detail, the noise is like happening in all cylinders at same time.

     Things made on the past two hours: Fine retuning, carbs balance checked (ok), temps measured (with infrared thermometer) at both inlets and oulets of mufflers with minimal differences (10º) between inlets and between oulets. Changed one spring (0.031" to 0.047" wire d.) and made a street drive test. It felt with stronger pushing over 2,000 rpm (1st to 3rd) but, no chance to make it on 4th. Will wait for next chance on real roads. 

      Thank you very much and... best regards.

      Daniel

       
  ----- Original Message ----- 
  From: BobHelt at aol.com 
  To: dmonasterio at megared.net.mx ; virtualvairs at corvair.org 
  Sent: Tuesday, August 30, 2005 5:04 PM
  Subject: Re: <VV> Weird clattering


  In a message dated 8/30/05 10:47:32 AM US Mountain Standard Time, dmonasterio at megared.net.mx writes:


    On flat roads there is no major problem if I accelerate gently between the 2,500-3,000 rpm area. 

       What do you think about ? Maybe the camshaft ?

       Thanks in advance for any arrow in the right direction.

       Daniel



  Daniel,
  Can you distinguish whether this sound is detonation (spark knock) or something mechanical? If Detonation, consider colder spark plugs. In fact what do the plugs look like? Short out one plug wire at a time at the distributor and see if the noise changes when you run and accelerate per your description.

  If a mechanical noise, consider a collapsed lifter. Does the noise cease immediately when you let up on the accelerator? In not, could be a lifter. Sorrt to sau, but a broken crank could also cause a mech noise under these conditions too. Probably not a camshaft problem. Maybe there is something scraping when you accelerate.
  Regards,
  Bob Helt