Wheel Bearing Preload Change Over Time

[Pmerems]

I performed my condition inspection this week. This is my 8th inspection (9 years flying-415 hours on the RV-7A, surely not flying enough)

While servicing my wheels and brakes (Cleaveland Wheels with Timken tapered roller bearings) I noticed a polished area on my left axel. I wondered if the bearing inner race spun and caused this polished appearance. The surface doesn?t have any ridges, just smooth. During my cleaning for the parts I also noticed that one of the aluminum outer bearing spacer rings had a slight impression where the brake mount tube contacts the spacer ring (the one that slides over the axel and has the break caliper flange welded to it).

During reinstallation of the wheel I noticed that I could not align the cotter pin with the nut tightened down for the appropriate preload. I had to back the nut off slightly to get the cotter pin in.

Flash back 10+ years and during my build I had issues drilling the cotter pin hole in the axel. I ended up using axel shims to get the preload I wanted. I am sure many have had their struggles drilling these holes and getting the preload correct.

To the correct preload after 9 years of flying I added a .004? axel shim. This is the first time I had to make an adjustment. Now after needing this adjustment the evidence of the polished surface on the axel and the slight impression on the aluminum outer bearing spacer all makes sense.

I decided to share my experience because I am sure there are many owners who have or will have this issue. It is simple to correct if caught before any permanent damage is done.

I hope this helps.

[snopercod]

Originally Posted by Pmerems

I noticed a polished area on my left axel. I wondered if the bearing inner race spun and caused this polished appearance.

That's what it sounds like. My Lancair has bearings that need preload and, when I didn't torque the nut enough, I got worn areas on the axles. I have to tighten mine until I only get about 2" of travel when I try to spin the tire. It seems too tight but that's the way it's supposed to be done. Matco came up with improved axles that have a large flange on the inboard end and the axle nut to provide more surface area to resist the tendency of the bearing to spin.