It looks to me like this engine mount was
not stress-relieved after welding. Any 4130 weld should be stress relieved to
eliminate the “brittleness” and high stresses at the weld due to
the rapid cooling and localized hardening at the weld area. Engine mounts and
landing gear would be critical items typically made from 4130 tubing weldaments
requiring stress relieving. Stress relieving requires 4130 requires 1100 degF
and slow cooling.
To determine if the mount was stress
relieved, take some hardness strikes (readings) at the weld area and then
several more ½” apart for several inches from the weld. The hardness
profile would show higher readings right near the weld.
-Neal Garvin
Glasair SIIS-RG
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf
Of Jim Nordin
Sent: Saturday, August 25, 2007
5:36 PM
To: lml@lancaironline.net
Subject: [LML] ES engine mount
cracks and breaks
Here’s a note from Lon Kelley
regarding his ES motor mount issues. I hope these pictures will encourage you
all to examine closely … very closely … your motor mount.
Personally I don’t see how there wasn’t a very serious accident
because of this problem … Lon and Pam were just plain lucky.
Jim Nordin
From: PKkelle@aol.com
[mailto:PKkelle@aol.com]
Sent: Saturday, August 25, 2007
3:40 PM
To: panelmaker@earthlink.net
Subject: ES engine mount
Jim, here is some information on the recently discovered engine mount
problems in my ES. The pictures are attached and show some major breaks and
widespread cracking in the welds. It is my opinion that these cracks indicate
improper welding procedures in my mount, and there may also be a problem in
other early ES mounts. I have not got any professional opinion on the welds,
and really don't intend to, but the cracks all appear to be in the
heat-affected zone adjacent to the weld, and this is the area of concern in
most high carbon material where embrittlement might occur.
I believe these cracks have been there for a long time, and we missed
them during inspections. My only excuse for this is that they wouldn't be
visible under the paint. What led to my finding them was some very rough
taxiing at Sun N Fun, Oshkosh
and a rough grass strip this summer. At the last oil change I specifically
wanted to look at the nose-gear mount, and feel very lucky that we took the
bottom cowling off, and I stuck my nose down there and chipped some paint back.
Of course the two broken members were pretty obvious if you were looking. My
plane has 1225 hours and this mount was made in 1994.
Incidentally, we sent our strut back to Lancair in about 1999, and Vern
rebuilt it. We have not experienced serious shimmy with it, and I don’t
believe the weld cracks are associated with shimmy. Lon Kelley