REFLECTOR: Lycoming head thread

[davedent at comcast.net]

Lycoming head threadkeith there are two sizes.  1/4-28 or 1/4-20.  The ones on the face of the cylinder are normally 1/4-20 for the valve cover and the ones on the fwd and aft are the 1/4-28.  It's best of you see what screw you can put in, without forcing it. The plugs that are on the intake are 1/16 pipe.  Check out your parts catalog, if not sure. They are called out in it.  If you don't have the parts book give me a call.  I'll be at the hangar for a short time today.  925-337-0115
Dave
  ----- Original Message ----- 
  From: Keith Hallsten 
  To: Velocity Aircraft Owners and Builders list 
  Sent: Wednesday, July 04, 2007 8:33 AM
  Subject: REFLECTOR: Lycoming head thread


  Does anyone know what thread is in the screw hole in the side of a Lycoming cylinder head?  I need to attach a clamp to support the lower ignition harness as it "turns the corner" at the #5 cylinder on my IO-540 parallel valve nominal 260 hp.  

  There is a hole that appears to be sized for a #8 screw facing the firewall, but when I tried an #8-32, it will only thread in for most of one screw revolution.  It's hard to see, but I suspect that the thread pitch is larger than 32 threads per inch (that is, fewer threads per inch).  However, #8-32 is in the "National Coarse" series, and I don't know of a commonly-used coarser thread standard.  

  This hole looks as if it was intended for the attachment of baffles.  It could be that there is some paint or something in the hole that is causing the resistance, but I don't want to chase the threads with a tap until I'm sure that they aren't some other pitch!


  If the thread really is an oddball, I'll also need suggestions of where to buy a couple of appropriate screws! 

  Thanks for any help you can offer

  Keith Hallsten  



------------------------------------------------------------------------------


  _______________________________________________
  To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector

  Visit the gallery!  www.tvbf.org/gallery
  user:pw   Check new archives: www.tvbf.org/pipermail
  Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.tvbf.org/mailman/private/reflector/attachments/20070704/5372fd94/attachment.htm