Nose Strut

From Bondline

Contents 1 Introduction 2 What if it's STUCK? 3 Inspection of the Strut spindle 4 Torque Tube Box

Introduction

The factory recommended annual removal of the nose strut is probably one of the most disregarded maintenance tasks on the Grumman fleet. Frequent excuses about it being complex and time consuming are just not true, and probably spread by those that have never actually DONE it.

The intended purpose is not to run up the labor costs at annual, or to scare away Cessna mechanics from working on Grummans. Its to allow inspection of the nose strut on the inside and the outside. The strut is made of a high strength alloy steel. These type alloys are not particularly good at resisting corrosion, and the hollow nose strut is subjected to fairly high loading while just PARKED with the weight of the engine being supported.

The actual pulling of the strut can be somewhat anticlimactic. After the lower cowl is removed and the flexible rubber boot is removed (not installed on 77 up planes with the 2 small "shock absorbers" mounted to the strut), there are only 2 bolts that hold it in. They are special NAS shear bolts and are matched to the holes with a reamer. With the forward portion of the fuselage properly supported, such that the nose is raised several inches above the pavement, the 2 bolts are removed. Usually they will require a drift and a mallet to tap them out. At this point, if the plane has been properly maintained in the past, the nose strut can be grasped and rotated to shear the zinc chromate that was used to seal the strut to the socket. After rotating several degrees, pulling forward while rotating the strut side to side will slide it right out. If your nose strut has been inserted with "bear grease" as a few Grumman owners suggest, it may slide out by gravity after the bolts are removed. This isn't a good thing, as the freedom of the strut to move may create a "bolt cutter" effect by allowing the forces on the strut to try and shear the bolts. It is a stretch to think that this would happen, but its not what the manufacturer's instructions say to do, therefore it is improper. Also grease may not protect against moisture, since the grease is thickened with compounds that can absorb water.

What if it's STUCK?

If the nose strut hasn't been taken out regularly and then properly re-installed with wet zinc chromate, then it may be harder to remove, due to corrosion in the socket and on the strut binding it.

The first step in removing a strut that resists rotation by hand, as described above, is to lube the strut and socket with a penetrant. Most any "bolt loosener" penetrant will work, but my personal favorite is Mouse Milk. As with all penetrants, some patience is required in order to give the lubricant a chance to work. Take a lunch break and give it an hour or two.

If it still resists moving by hand after the penetrant has had a chance to work, a temporary tool can be constructed from a 4x4 piece of lumber and a couple 1/2" bolts. Having a 10 foot lever arm allows quite a bit of leverage to be applied. Even a small movement is a victory, since that will allow the penetrant to seep into areas previously unlubricated. Continue side to side movement and continue to add penetrant through the bolt holes. Direct the penetrant spray up the strut, so that it will run over the edge and find its way between the socket and the strut.

Inspection of the Strut spindle

It is not necessary to remove the strut to inspect the spindle where the nose wheel fork pivots. This is a regular 100 hour/annual inspection item. The spindles are subject to corrosion when the o-ring that seals the strut-to-fork intersection is damaged, missing or incorrectly compressed due to improper shimming of the fork to the strut. Water leaks in where the o-ring should seal, and flows down into the socket on the nose wheel fork, contaminating the grease.

The spindle should be clean, unpitted, and cylindrical. Out of round or taper in the spindle causes the nose fork bearings to have play and/or wear excessively. Wear in the spindle and bearings translates into vertical movement of the nose wheel axle. This prevents the belleville washers (shimmy damper) from working correctly. The loading changes with the weight applied to the axle, rather than remaining constant.

Torque Tube Box

These instructions begin after airplane is properly on jacks, and the nose strut and nose wheel are removed. The upper and lower cowlings will be removed during the process, so taking them off before getting in the plane may be helpful.

Jason Bowman tells his story of removing the nose strut torque tube assembly:

Hopefully you are 5’2" tall, with the reach of someone 6’5", weigh about 100 lbs, and you are a dentist who is used to working upside down and backwards. Really it helps.

The service manual instructions were the basis for this article, but it lacked a few helpful techniques.

1. Remove the front seats. The details on seat removal are slightly different for the 2 place and 4 place models.
   1. 2 place models. The seat bottom may be lifted for access to the forward seat attach bolts at the spar. There is one AN3 bolt on each seat rail. Remove it and detach the springs, and the seat will slide forward and up out of the rear brackets on the floor.
   2. 4 Place models. The seat is attached to brackets on the spar, and there are 2 clevis bolts (look like slotted screws when you are trying to find them) that are at the forward side. The seat latching mechanism can get in the way because the latching pawl pins fit into holes that are on either side of the clevis bolt heads. Remove the 2 clevis bolts with a straight blade screw driver. It may be more convenient to slide the seat to the position where the holes in the seat pan align with the locations of the clevis bolts, thus allowing SOME visual confirmation of the positioning of the screw driver. After the 2 clevis bots are removed, the seat will slide aft and out of the brackets.
2. Remove the front console side panels also remove the left side fresh air box. It is right under the yoke. There are two Phillip head screws holding it on. You will need a long #2 Philips screwdriver to reach up through the bottom of the airbox. Look for 2 holes, possibly with snap in caps to seal them. You will also have to disconnect a drain tube coming up from the floor side panels.
3. Remove the front side panels (kick panels near the floor) on both sides of the plane. Some of the screw holes may be hidden by upholstery and trim.
4. Remove the lower cowling. As suggested at the beginning, before climbing into the plane.
5. Remove the rudder return springs. Note, the manual says remove the eye bolts from the firewall etc. I didn’t and it wasn’t necessary. But now would be a good time to think about adding new springs if you have them. (I have spares in the plane.)
6. Remove the co-pilot side right rudder bar attach bracket. It has two 3/8 nuts holding it to the floor. When you remove it the rudder bar can be moved up and aft to help remove the brake cylinders around without disconnecting them and allowing air into the system.
7. Remove the brackets from the co-pilot and pilot side brake cylinders. Pay special attention not to bend them too sharply after you disconnect them. I disconnected the clevis pins right behind the top of each pedal so I could lay the pedals down and get a better shot at the other nuts holding all the cylinders down.
8. Remove the clevis pins on the rudders (Been there done that, too!)
9. Remove the parking brake connection to the pilot side master cylinder. ( I didn’t have a parking brake)
10. Move the brake cylinders up and away and secure them out of the way so you have room to remove the torque tube later.
11. Remove the throttle cable and clamp screws from the instrument panel brace. I didn’t I loosened the whole panel brace by removing the six 7/16 nuts.
12. Remove the nut and bolt that holds the T-column to the floor. I didn’t when I moved the instrument panel brace the T-column moves with it. It has to move aft or you would not be able to get the torque tube assembly out on the pilot side. I did not touch any cables or pulleys to move the brace.
13. Remove the six nuts that hold the center bracket for the torque tube assembly from the outside near the firewall. Someone else will have to remove the nuts as you hold the bolt inside with a 9/16 wrench. Work out the bolts and a small L bracket on each bolt completely.
14. Remove the four snap plugs on the lower front of the fuselage. (I always wondered what was behind those things, now I know!) There are four bolts that have to be removed. Two on each side. Do the pilot side first. It is easier to get at. The forward nut is inside the cabin and is difficult to get a wrench on. Get a 9/16 socket wrench (a box end or open end one side and a socket on a 90 degree swivel on the other end.) Have your helper remove the bolt from the outside as you hold the nut from the inside to keep the nut from turning… have fun. Do both sides co-pilot side is very tight on the front bolt. Get creative with the way you hold the nut as the helper turns the bolt. Remember you are almost done.
15. Remove the torque tube assembly from the pilot side. There may be a spacer for each side of the tube assembly next to the outside wall. Pull the yoke aft to help clear the space. It helps to get the center bracket clear first by pulling it up and aft, then you can pick up the pilot side higher and the tube will move. Be careful with the brake cables, don’t jerk anything around, it will come out, but pay attention to how everything is routed so you can put it back the same way it came out.

Read the service manual for reinstallation and torque values. Make sure you have everything inspected properly and clean up the goo on the floor under the pedals. Mine was loaded with small washers from (somewhere, sometime) and lots of sticky nasty dirt. A clean plane is a happy plane! Good luck, your experiences may vary on this project! I lost 5 lbs of sweat doing this job in about 7 hours removal time.