Check the following: Nose Strut Pressure, exposed piston should be 3.25" plus or minus .25", Tire Pressure, torque link play, tire inbalance, or even incorrect preload on the nose wheel bearings. Just a few things to check...
Check the torque link bushings first and foremost. I had the same problem, a shimmy that showed up over time, and based on JimC's other posts in other threads I had my A/P check them out. All they needed was a tightening, which he said took 10 minutes and didn't even charge me for.
(Of course, he knows he's got the annual starting in two weeks...he'll get it all back in spades!)
Loose Nut and Nosewheel Shimmy
March 15, 2004, 3868
I experienced some nose wheel shimmy on roll out the other day. On checking I found that the nut on the bolt that holds the belkcrank to the top of the nose strut had worked loose. Tightening this eliminated the shimmy.
I would recomend checking this nut on a regular basis as a friend at the field recently had a $5000 repair for nose wheel shimmy as it cracked the engine mount.
Main Gear Shimmy
February 25, 2004, 4337
A week or so ago, as I was taxiing back to the hangar another pilot told me my left main had a shimmy. I found the castle nut had a lot of play.
When it was removed and cleaned a couple years ago, it was tightened according to specs (finger tight then one more turn). It had about 2 turns to get it finger tight. Apparently, when it was done last, the bolt did not come up completely. As a precaution now, I will check it a week or so after any maintenance to be sure it is tight. No shims were needed.
Severe Shimmy
There are several things that can contribute to that. First check the bell crank on top of the nose gear strut to see if it loose. You might want to have someone inside to try to move the rudder pedals (slightly) while you observe to see if there is movement with the nose wheel not moving. It is my opinion more than likely its the bushing/bolts in the scissors that are worn causing the problem. The bushings are very cheap from Kansas City Aviation. Next I would check tire pressure and tire balance. I have seen low pressure do the same as well as out of balance tires. Contrary to popular belief, the last place I would suspect is the Shimmy dampener which can cause it but the other items or more prone to be the culprit.
Test For Shimmy Damper Operation
Sounds like maybe your shimmy dampener might be at fault. Jack up your plane getting the nose off the ground. Then, move the nose wheel all the way to one side and let go. If the nose wheel snaps back to center then the shimmy dampener is defective. Instead, it should come back somewhat slowly, maybe taking a second or two to get back to center. Another test to do is to move the nosewheel in one direction to the halfway point, then move it back and forth a little. You should feel some stiffness and no breaks in that stiffness. If you feel any breaks then the dampener has lost some of its fluid. I have a complete documented procedure on how to rebuild the dampener at "The Eagle's Nest". Click on "Maintenance". However, some are not rebuildable.
Repair Steering Horn to Stop Nosewheel Shimmy
Shimmy can be caused by the steering horn on top of the nose strut that the steering arms connect to. If so, I removed mine and had a machine shop drill the elongated holes out and insert replacement bushings which were then welded in place. Makes a nice repair.
Nose wheel Shimmy
Try to adjust or tighten your scissor gear. Typically tighten the bolts and lube the strut first. This fixed my 140 instantly, as it shimmied very badly under braking between 36 and 65. Don't forget to check tightness of the hardware on the scissors gear on the mains too. That one cured mine once upon a time.
Nosewheel Shimmy - Causes
Most probable culprit is the shimmy damper - replace the 'O' rings and re-service. Other things to consider: both main and nose wheel sissors bolts and bushings, all wheel bearing preloads. Warped brake disks, Wheel alignment, rudder control cable tension. and the nosewheel strut bearings. Pretty much in that order.
Nosewheel Shimmy
Things that should be checked: (easy things first!!) Shimmy damper, wheel bearing (all) preload (retaining nut tightness), main and nose wheel sissors bushings and bolts, and main wheel alignment(toe in), control cable tension, steering rod end bearings. Seems like a lot, but any one can be the problem, and may excite one or more of the others. In my case, it was the main gear alignment, MG sissors and the shimmy damper, in concert.
Don't forget about the steering horn that mounts to the top of the nose gear strut. The holes will wear and cause looseness in the steering linkage. A couple of ways to repair is to replace the horn, drill out and re-bush the holes, or weld holes closed and re-drill.
Check the bearings and repack. Check the "true" of the wheels and make sure they are straight. Check the air pressure. Check the tire. Had the same happen to me on landing and it was all of the above plus the shimmy dampner.
And....
The one rarely monitored and probably the biggest culprit. There are the mediocre bearings inside the strut mount. These bearings are used in an incorrect application, they are not designed for thrust loadings. But kept in good condition and properly set preload will last quite sometime, 35 years, if they've never been replaced is way out of the envelope.
They develop cavities from wear in time and often will force the strut to steer improperly, and start to shimmy. If all is in good order, and proper weight distribution to the nose gear, allowing correct caster angle, "you do not need a damper", but it's a rare case.
Just did some repairs on the nose strut on a Tri Pacer, which is identical to the Cherokee. Worse, it has even less caster angle than the Cherokee, Had to make a non standard repair, not for discussion, and it will not shimmy without a damper, but just the same it is part of the package, and ideal conditions will not always be there.
Don't get too nuts about the damper. My old Cruiser's damper was half worn, but once the entire strut and all related parts were serviced, the shimmy was gone. The price of the damper prompted me to dig even deeper.
Rebuilding Shimmy Dampner
I've found I can rebuild mine. Here's the procedure I put together to do it.
Shimmy Dampener Rebuild Procedure
---------------------------------
Nose wheel shimmy dampener:
Piper part number: PS-50152-7
Cleveland Wheels & Brakes
Aircraft Wheels & Brake Division
Parker Hannifin Corp.
Akron, Ohio 44011
Cleveland Model NR: 15-10
Ser Nr: 200
Manufactured: 04/90
O-rings used for rebuild:
MS28775-112 (qty = 2), use Spruce #AN6227B-10
MS28775-008 (qty = 1), use Spruce #AN6227B-3
MS28775-210 (qty = 1), use Spruce #AN6227B-15
Piston nylon ring generally doesn’t need replacing. Just replace the above O-rings.
Note: There is a small piston in the rod that has an O-ring that needs to be replaced. Piston can be removed with a 4x40 screw threaded down its middle. The MS28775-008 goes on this piston. Note also, that the dampener has a fill hole accessable by removing the small plug. Fill dampener with MIL–0-5606 hydraulic fluid through fill hole. Be sure to purge all air from the unit, including the center of the control rod, before closing it up. Only fluid should exist on both sides of the control disk throughout the cylinder. Cleveland no longer manufactures this dampener, and Piper no longer supports this dampener. If dampener must be replaced it will have to be replaced with a different type unit, at $500 - $700 cost. Get replacement O-rings from Spruce or O-ring dealer. But, be sure they conform to MS28775
Nosewheel Shimmy
The one item that we all seem to forget is nose wheel balance. In many cases I have been able to stop the shimmy on Cherokees by balancing the nose wheel when every thing else failed. Unfortunately,I have found very few 600-6 tires that didn't need balancing. Just food for thought. Before you spend alot of money rebuilding parts, check your wheel balance.
Nosewheel Shimmy
Reasons for shimmy:
1. Bad tire
2. Incorrect oil and/or "air" is strut.
3. Worn strut bushings
4. Per Tom, SL, cracked motor mount.
5. Worn strut bearings or incprrect pre load.
6. Worn seals and wiper
7. Bad or incorectly loaded wheel bearings
8. Bad shimmy damper.
9. Bad scisors
10. Loose fork mount.
Aircraft records on CD
I received my CD the other day. It has copies of all of the orignal documents filed with the FAA, including registration applications, airworthiness certificates, 337's etc. It was neat to see the history of the aircraft's early ownership.
I found copies of two letters to the FAA, one from a flight scholl requesting to change the n-number on my bird and two others to numbers they had reserved for aircraft in their current fleet. A month later, another letter asking for permission to change it back. They were selling the aiplanes for new ones, and never did renumber mine...after all my '68 Cherokee was almost two years old in 1970, obviously time to trade th "old" bird in.
Very cool stuff, definately worth the $5. The web-site says you need a credit card, but it never did ask me for mine, however. The CD showed up in the mail, with a bill for $5. (no additional $ for shipping).
You can order at:
[diy.dot.gov]
Click through on "Federal Aviation Administration" then "Aircraft
Payments" then "Request for Copies of Aircraft Records"
Nosewheel Shimmy
Having been the proud owner of a 140 Cruiser, this is how the shimmy was fixed. First and foremost any wear in leg bushings, oil leaks, proper oil level, and air pressure, must be attended to. Scissors should be in good order, and damper as well.
The culprits are the two ball bearings (452-332 & 453-332) in the strut housing. They are not made for this task. They "rot" easyly if not lubricated, and are easily damaged if not tightened properly.
They develop "craters" on the races , and prevent the aircraft from being steered. Move the steering and the bearing goes from one "crater" to another, or shimmy.
Main gears should also have proper toe in. Toe out will induce the nose gear if it has worn bearings.
Engine Running Lean or Rich
Sounds like mixture control needs adjustment. I spoke to the rebuilder this morning who worked on my carb. Got a earfull of physics and wished I had recorded the call. He sugggested the following can be done to gauge the health of a properly "adjusted" installation:
At runup set wide open throttle and note RPM. Lean to max RPM. Should be not more than 200 RPM and not less than 100 RPM change. If less than 100 RPM you’re too lean and if more than 200 your too rich.
Nosewheel Shimmy
I got this problem on my 77 PA-28-151. My nosewheel would shimmy while taxiing and occasionally when decelerating after landing. I had the shimmy dampener replaced (it was very loose to the touch and would no longer hold the pressure when actuated) and the shimmy went away.
It was a bit expensive though because the piper part is not repairable so I had to buy a new dampener. So you might want to look at the dampener and have your A&P see if it is still serviceable
...and...
I fought this for 2 years with 2 local a&ps looking at it.They told me to try replacing the shimmy dampener and when I took it off found it had sufficient damping and was not leaking.I finally fixed it myself in 5 minutes at no charge! Have some one press on the stabilator untilyou extend the nose strut entirely,lube the scissor gear,then lube and clean the strut with proper lube and then tighten the scissor gear bolts until the strut will not move,then loosen the bolts slightly and work the srtut up and down until it moves freely,keep it clean and hopefully it will cure it.Mine was terrible and it got worse with a load or heavy braking.As for the shimmy dampener I know several people who have removed them with absolutely no degradation in performance...I am not advocating this but I think too many a&ps look to the most expensive option they can.
Nosewheel Shimmy Cure
I had the same problem a while back with my Archer. I got a shimmy on braking and it was made worse when the nose strut got a little low. I put new bushings and bolts in the nose scissors and it cured the problem. Put some muscle into shaking the nose scissors. If it moves even a little bit, you need to tighten it or new bushings/bolts. They are not hard to install and they are the first, cheapest fix to try.
And...
Lift the right engine cowling as though your about to put in oil, remove the retainer clip from the pin that runs through the top of the front stut bracket,(don't move nothing!) slide in a 1/4 in. aviation quality bolt that is long enough to get a self locking head on. Tighten it down snugly. Don't over tighten. Go try some taxiing to see if this helps. If it does help you know the play is caused by the top bushing and the mount holes being woolered out. I do not advocate you leave the bolt in there because that would be an unauthorized mod but it will confirm where its coming from.
Adjusting Carburetor Heat door
Sometimes making the carb heat seal both open and closed may be impossible.
On one Cherokee 140 I worked with, the round tube against which the butterfly valve is supposed to seal was asymetrical... so you could only get a good seal open or closed , but not both. This may be the case in many carb heat systems, due to distortions caused by the welds.
Having the heat portion open even a little bit will raise your intake temperature a lot ( fifty degrees comes to mind ) and will rob your engine of up to five horsepower. So if I have to make a choice, I'd get the valve to close off the carb heat rather than let the heat leak in when it's supposed to be closed.
In order to get a good seal in either position, you'll probably have to rebuild the butterfly valve, using a new flexible membrane, cut slightly oversize. AND you're going to have to make sure that the valve's shaft has not worn out the bearing surface.
All together this is a difficult and messy job... but it's important.
Hy dog boy Jim C hit the nail on the head i to Hade the same fault, with my 1977 Cherokee, replaced the nose bushes replaced and all ok,i also found that if firm rudder pressure, was not apllied the nose wheel would shimmy like a bastard.
They are checking my front end as we speak for the nose wheel shimmy and have found a crack in the torque link,are they expensive and where do you get new torque links?
if you torque link is stamped sheet metal, I'd bet it could be welded (check with A&P).
Stevee
I don't have the part #s for the Warrior II but you can get them from a downloaded parts manual at [www.bomar.biz]
I just replaced all my bushing s and bolts with new from Piper and they weren't expensive.
