Bucky is right.  low nose wheel inflation can lead to "cupping" or scalloping of the outer edges (hard to see) which feels like shimmy.

 

Grayhawk

 

First check wheel bearing pre load. ( less than a complete revolution when
spinning by hand. )
Check the through bolt at engine mount to gear for tightness, but do not
overtighten or will not free fall.
Check welds at nose gear to engine mount for cracks.
Check tire inflation  ( I use 32 PSI in my 360 nose gear )
Check wheel and tire for balance.
Check mains for flat spots and ( 45-50 PSI )
I do not have a self centering strut and has never been a problem.
Bucky Whittier
360 BB






----- Original Message -----
From: "Greenbacks, UnLtd." <N4ZQ@verizon.net>
To: "List Lancair Mailing" <lml@lancaironline.net>
Sent: Friday, February 22, 2013 4:34 PM
Subject: [LML] Nose Gear Strut


At the moment, my focus is intently riveted on my nose gear strut.
On the 10th landing back at KBVY yesterday, I felt (for the first time), a
momentary vibration in my control stick. It was brief, maybe lasting 2
seconds. I have no idea what nose wheel shimmy feels like, perhaps one of
you with experience in this area could elaborate.
So here's what I've got, my strut dates from 1995 and is not self centering.
I've got 4ZQ up on jacks and and when turning the nose wheel from
side to side, there is no sound that might indicate air bubbles inside. I do
notice that there is greater resistance when turning the wheel to the left
as compared to turning to the right. There is some evidence of oil dampness
on the strut. I have not yet removed the fork to see if there is any oil
pooling up inside. At this point, I'm guessing that if this were the case, I
would see it leaking down along the fork. I'm told by Ross at the factory,
that the principle cause of nose wheel shimmy is a lack of fork oil, no
oil....no dampening, etc.
So my plan is to release pressure from the strut, check the oil level and
cycle the strut up/down until there is no sign of air bubbles. I got some 20
weight fork oil from the local Harley dealer. My plan with the strut
extended and full of oil is to collapse the strut, close the valve, set the
plane on its nose wheel and re-pressurise the strut, and go fly.

I'm all ears for nose strut advice/suggestions.

Angier Ames
N4ZQ



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