Message-Id: <5.1.0.14.2.20011209192059.02436910@pop3.olsusa.com>
Date: Sun, 09 Dec 2001 19:22:39 -0500
To: lancair.list@olsusa.com
From: Marvin Kaye <marvkaye@olsusa.com>
Subject: L320 - nose wheel shimmy cracks engine mount?
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Reply-To: lancair.list@olsusa.com

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Posted for "colmar" <jones@colmar.demon.nl>

Just de-cowled today, (with a view to finally sending my old-style nose gear
strut back to Vern for all those revisions of the oleo, incl. self-centering),
to discover that the horizontal element of the engine mount just above the 
strut attachment points (those parallel vertical planes) is severely 
cracked at both left and right ends where its welded to the rest of the 
engine mount assembly.

Anyone else had this experience ? Is it safe to assume that it IS due to 
nose wheel shimmy?

I have had shimmy only occasionally over the 200 hours so far (and never been
able to correlate it to anything in landing technique, tire pressure, etc). 
But whenever it happened I, without much experience of shimmy in other 
planes, found it quite violent - although no affecting runway tracking.

Could there be another factor involved? for example;
Since this cracked engine mount element is so close to the parallel vertical
planes defining the strut/mount interface, how sensitive is the fit of the 
strut into the engine mount gap? Since this gap is essentially defined by the
dimensions this engine mount element so close by, this element could obviously
be put under a lot of compression if the long holding bolts were clamped tight
onto an smaller-dimensioned strut fitting. I remember it being a tight fit 
when I was building, but are we talking here about "file-to-fit, or 
polish-to-fit, or push-fit or interference-fit" or just "bolt-in-place" ? 
In which case, what bolt torque?

Advice? (for eventual installation of revised strut in a new engine mount -
hopefully before Spring arrives ! )

Colin Jones (PH-COL)

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