Since last Fall I had been noticing bearing looseness in the front nose wheel. I could tell that there was an issue because I would hear a whizzing sound from the nose wheel when I lowered it to the ground after landing.
The connecting bolt for the nose wheel that secures it to the nose gear fork is an AN4-40 bolt, secured with a castle nut and cotter pin. The castle nut squeezes the fork against th wheel bearings, and there should be no float and only 1.5 to 2 turns possible if the wheel is spun by hand.
I removed the wheel and the bearings in December and checked them carefully to ensure that they were not wearing out. I found no significant play in the bearing races, so I repacked the bearings and re-fitted them to the nosewheel.
The clue as to the root cause of the problem came when I discovered when tightening the castle nut that the torque on the castle nut would rise, then slacken off, then rise again. This pointed to either a worn-out castle nut or bolt, or both. Examination of the castle nut and bolt threads showed that they were both severely worn. I replaced the castle nut, and this supported an increased torque limit, but then the nut would jump across a thread and the torque would drop again. Because of the worn threads there was insufficient squeezing force on the fork to tightly clamp the bearings into the wheel, hence the small amount of bearing float that was leading to the whizzing and chattering noise.
On Saturday I managed to locate an AN4-40 bolt from a guy who owns a workshop adjacent to the Lancaster Airport. I repacked the wheel bearings, and fitted the new bolt and a new castle nut. I was able to load the castle nut torque to a value where there is no longer any bearing free play, and the wheel spins for 1.5 - 2 rotations when spun by hand. I performed several full stop landings to check the operation of the nose wheel. The noise has gone, and everything seems to be operating normally.
The worn-out bolt had been on the plane for 14 years and 550 flying hours. It is difficult to know exactly how many times it had been removed from the plane, but I would guess that I have been removing the bolt at least 2 times per year - once at the annual, to repack the wheel bearinsgs, plus some other removals due to nose gear maintenance.
I would recommend that this bolt be lifed at 10 years maximum. A replacement will cost $1.50 from Aircraft Spruce, so we are not talking about spending much money here.