PCV rattle trap
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    Thread: PCV rattle trap

    1. #1
      Junior Member
      Join Date
      Nov 2017
      Upstate NY

      PCV rattle trap

      I have my fully rebuilt B18D purring like a kitten except....the PCV valve rattles like crazy. I replaced the valve but it still rattles a lot. Its kind of a distracting sound from the otherwise sweet sounding engine. Any ideas on how to quiet down the PVC valve? Thanks.

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    3. #2
      Junior Member
      Join Date
      Feb 2014
      northern New Hampshire
      Spray some aerosolized grease (not oil), white lithium or regular petroleum-based, down along the inner edges of the top nipple so it can run down and dry and form a lower "cushion" for the plug.
      Quiets it down for 1-2K miles.

      Or try this...remove and shake the valve REAL HARD a couple dozen times, and re-install.
      '62 Amazon Original 65K mile time capsule
      '94 MBz E320 wagon 120K miles '92 MBz 300CE 2Dr 180K cold weather miles
      '94 MBz E420 120K miles '86 BMW 635CSi 2Dr 180K warm weather miles

    4. #3
      Junior Member
      Join Date
      Apr 2016

      PVC Valve rattle is a condition (annoying, but otherwise not really harmful) which occurs when the frequency of pulses of vacuum at idle is equal to the resonant frequency of the return Spring and Mass of shuttle/ball in the Valve, in combination with the volume inside the PVC plumbing...its a pretty specific confluence of conditions (like hitting the mechanical lottery!) that happens occasionally (but only at idle, where frequency of the individual pulses are slow enough, and don't yet combine into a steady vacuum)...change any one of the critical parameters, and it will stop...so much for the theory (my good friend was a physics teacher, so I had to get this right or I would never live it down!)...

      in practice, the simplest solution to prevent resonance, is to just change the exciting frequency a bit, by just changing the idle RPMs a little (that's what did it on my 122/B18)...if that winds up being too high or too low to be an acceptable solution, another possible preventative is limiting the excitation pulses the valve is seeing, can do it too (by adding a partial flow blockage [washer] with a hole in-line into the PVC plumbing to partially orifice block it...to see if this might help, simply squeeze the line partially shut to try it)...or creating a little buffering volume in the PVC plumbing by installing two flow limiting orifices, one at the manifold, one at the Valve, or plumbing in another length of (dead-ended) tubing with a "T" (kinda like the expansion tank on a furnace), finally, just replace the PVC Valve...what are the chances that replacement Valve will be resonant also...but where's the fun in that? Edit: I guess you already tried replacing it, and it still rattles...try replacing with a different style/manufacturer Valve, or I guess it would be time to try one of the other suggested solutions...

      Good Hunting!
      Last edited by Ron Kwas; 02-25-2019 at 11:14 AM.

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