Teflon headers, followup

[Bob Kane]

I bought two sizes of tubing, the 5033K39 is 5/8 ID, 3/4 OD with a 1/16 wall thickness for the header tube, and 5239K19 which is ID of 3/4", OD of 53/64" with a .040" wall thickness to use as a bushing on the header end where it clamps to the header brace.
 

Kenneth Blackwell <blackwellk at snowhill.com> wrote:
Bob,
 
Note that there is a thicker tubing that most of us are using. I think that it has a 1/16" wall thickness. I believe that this may be your problem. I have been using the thicker tubing for several years without a failure.
 
Cheers,
 
Ken Blackwell
----- Original Message ----- 
From: Bob Kane 
To: nsrca 
Sent: Thursday, October 09, 2003 8:31 AM
Subject: Teflon headers, followup


I thought I would let you know what is going on with my teflon header issues.  I was using blue teflon 5/8 ID, 3/4 OD PTFE ordered from McMaster-Carr, and getting as few as 6 flights from the header. Setup is YS140 Fizzle, Hyde mount, NMP High Performance header, Johnson SQ pipe on a single Lord mount. 
 
It was time to get some more teflon, so I ordered semi-clear part# 5033K39 (5/8ID, 3/4OD), and a short piece of 5239K19 (3/4ID, .040 wall thickness). The larger size is a slip-fit over the 3/4OD stuff. I use a 1.5" piece of it over the end of the header where it is clamped to the header brace. One other procedural change I made was to place the clamp over the teflon in front of the bead in the steel header instead of directly over it. The teflon formerly failed at the bead, moving the clamp ahead of the bead seems to reduce the erosion of the teflon.
 
Well, they still fail, but are lasting quite a bit longer. Now the failure point is right where small teflon exits the larger teflon bushing.  Judging from the looks of the header where it failed, it could be caused by torsional vibration between the Hyde-mounted engine and single soft point mounted pipe. There might be some kind of harmonic thing going on where the engine is going one way and the pipe is going the other, and the teflon has to twist. I have noticed the teflon softens quite a bit when heated and may not be up to the mechanical demands put on it from vibration.  
 
For those of you getting long header life, are your engine and pipe soft mounted? 
 
BTW, I must praise McMaster-Carr for their delivery service. I ordered on Monday morning, the teflon arrived Tuesday evening by standard ground UPS.


Bob Kane
getterflash at yahoo.com 

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Bob Kane
getterflash at yahoo.com

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