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CJcanuck
Joined: 05 Jul 2006
Posts: 39
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 Posted: Tue Apr 10, 2007 6:54 am Post subject: Nose Shimmy |
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Hi All!
Well, C-GYMK is on her way to Ontario, with a 3-4 week layover in Calgary where my co-owner is currently working. She's parked at CYYC at the Esso Avitat if anyone is in the area.
One issue that has come up is nose shimmy. It is apparently quite bad at anything other than taxi speed, and the oleo is extended quite a ways out when unloaded on the ground. The CJ tech manuals mentions 185mm nominal extension on the ground, but from the pictures I've seen the nose oleo is out more than that.
Any thoughts or fixes from anyone? Obviously the damper might be at fault, but how about a wheel balancing? Could a auto tire place do the balancing? Could oleo overextension cause this? Would bleeding off the oleo to 185mm extension help?
Thanks all!
Mike
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Joe Enzminger
Joined: 06 Feb 2006
Posts: 26
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| Posted: Tue Apr 10, 2007 8:04 am Post subject: Re: Nose Shimmy |
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My CJ had a similar shimmy that was solved by balancing the nose wheel. One of our other CJ's here had to actually replace the nosewheel tire. Although balanced, if you watched it rotate from the rear you could tell it was wobbling. A new nose wheel tire fixed that one.
I'd balance it first before you do anything more drastic.
Joe Enzminger
700YK
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wlannon(at)cablerocket.co
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| Posted: Tue Apr 10, 2007 8:12 am Post subject: Nose Shimmy |
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Mike;
The shimmy damper could be low or out of fluid but most likely the tire is
the problem. It should be balanced on the wheel and out of balance corrected
by the addition of a balance patch inside the tire. Most auto shops do not
have balance patches.
The oleo's on the CJ are (or should be) at full extension on the ground.
Oleo pressure should be 48 ATM main and 20 ATM nose (approx. 700 and 300
psi)
If the shimmy is not severe it may be possible to avoid by simply holding
the nose off on landing. If that will not work it must be corrected. Shimmy
will cause serious wear, cracking and other damage that will be very
expensive.
I could balance the NW tire for you but you would need to backtrack to
Oliver.
Cheers;
Walt
250-498-8387 hangar
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viperdoc(at)mindspring.co
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| Posted: Tue Apr 10, 2007 8:30 am Post subject: Nose Shimmy |
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Three things come to mind:
As you say, the tire could be out of balance for #1.
#2 The shimmy damper may need servicing. Is the pin on the end of your
shimmy damper opposite the knarled cap over the fill port extended out of
the damper housing or is it flush with the housing? If it is flush with the
housing, you need to service the damper for sure.
#3 Nose wheel bearings will also cause a vibration/shimmy.
Some auto tire companies can balance the the tire. You will have to pull it
take it to them and ask. Before doing that jack the nose up or pull down on
the tail and spin the tire. Does it look out of round when spinning? Do
you hear rubbing/grinding noises from the wheel with it spinning? Who did
you say did your overhaul/ assembly? Did they not test fly your plane
before you picked it up? That certainly should have been picked up before
hand.
As for the length and pressure for your nose strut, I can not comment on
that. One of the smarter CJ guys can answer that question.
| Quote: | [Original Message]
From: CJcanuck <m_kirk69(at)hotmail.com>
To: <yak-list(at)matronics.com>
Date: 4/10/2007 10:12:52 AM
Subject: Nose Shimmy
Hi All!
Well, C-GYMK is on her way to Ontario, with a 3-4 week layover in Calgary
where my co-owner is currently working. She's parked at CYYC at the Esso
|
Avitat if anyone is in the area.
| Quote: |
One issue that has come up is nose shimmy. It is apparently quite bad at
anything other than taxi speed, and the oleo is extended quite a ways out
|
when unloaded on the ground. The CJ tech manuals mentions 185mm nominal
extension on the ground, but from the pictures I've seen the nose oleo is
out more than that.
| Quote: |
Any thoughts or fixes from anyone? Obviously the damper might be at
fault, but how about a wheel balancing? Could a auto tire place do the
|
balancing? Could oleo overextension cause this? Would bleeding off the
oleo to 185mm extension help?
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dave(at)davelaird.com
Guest
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| Posted: Tue Apr 10, 2007 8:36 am Post subject: Nose Shimmy |
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Many times if a "new" nose wheel shimmy is caused by a broken shimmy
damper. The "shaft" in the damper that bolts to the gear leg shears
inside the "tube" of the damper...so you
can't just look at it and tell... but if you unbolt the thing and
open up the "tube" it becomes obvious! That's what happened on my
bird last year.
Also I noticed that when just moving the plane around on my tug that
the nose wheel seemed to have developed a mind of it's own....
after I installed the new damper shaft it behaved much better!
If this turns out to be your problem, Doug Sapp has an overhaul kit
for it that has all the seals and also a new stainless steel splined
shaft.
Hope this helps,
Dave Laird
N63536 1983 CJ6A "Betty"
Dallas
On Apr 10, 2007, at 11:04 AM, Joe Enzminger wrote:
| Quote: |
<panchoandlefty2002(at)yahoo.com>
My CJ had a similar shimmy that was solved by balancing the nose
wheel. One of our other CJ's here had to actually replace the
nosewheel tire. Although balanced, if you watched it rotate from
the rear you could tell it was wobbling. A new nose wheel tire
fixed that one.
I'd balance it first before you do anything more drastic.
Joe Enzminger
700YK
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=106073#106073
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rvfltd(at)televar.com
Guest
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| Posted: Tue Apr 10, 2007 9:03 am Post subject: Nose Shimmy |
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Mike,
I agree with Walter, but would add that if you have balanced your nose
wheel and tire as a unit (some wheels are worse out of balance than the
tires) and you still have a shimmy, check the splined shaft which sticks
out of the damper, this shaft will sometimes break off nearly flush if
the shimmy is bad enough and the condition is allowed to continue.
Another thing to check is the amount of slop in the nose gear scissors,
remove either the top or bottom, unfold the scissors and try to move
them side to side, you should have 1/8 or less slop side to side. The
third and in my opinion pretty much the last thing to check is the large
brass bearing at the tip of the nose gear. This are #'s 27 and 30 in
fig 4-3, on page 125, in vol #1 of the IPB. If these bearings are badly
worn this will add to the problem.
Most parts to overhaul are currently in my stock. Call me if you need
help on any of the above. 509-826-4610 office
Always yakin,
Doug
Walter Lannon wrote:
[quote]
Mike;
The shimmy damper could be low or out of fluid but most likely the
tire is
the problem. It should be balanced on the wheel and out of balance
corrected
by the addition of a balance patch inside the tire. Most auto shops do
not
have balance patches.
The oleo's on the CJ are (or should be) at full extension on the ground.
Oleo pressure should be 48 ATM main and 20 ATM nose (approx. 700 and 300
psi)
If the shimmy is not severe it may be possible to avoid by simply holding
the nose off on landing. If that will not work it must be corrected.
Shimmy
will cause serious wear, cracking and other damage that will be very
expensive.
I could balance the NW tire for you but you would need to backtrack to
Oliver.
Cheers;
Walt
250-498-8387 hangar
---
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