My plane (RV-12, S/N 120147) has approx. 370 hrs. I'm currently doing my condition inspection and found obvious free play of the axle inside the port side part of the nose fork. Upon disassembly and closer inspection, what is revealed is ovalation / wear in the Nose Fork Assembly (WD-1230) hole for the axle bolt.
As can be seen in the 1st attached photo, the port side hole in the fork has enlarged overall and become oblong (.390?) in the 11:00 & 5:00 o?clock positions as viewed from port side (i.e. 30 degrees aft from vertical). The starboard side hole has some enlargement primarily oblong in the same angle that matches the port side. The enlargement on the starboard side is minor in comparison to the port side hole. This is evidently due to the fact that the crest to crest diameter of the threaded end of the bolt is less than the shank diameter and the wedging action of the steel threads that slices into the softer aluminum. From the 2nd photo and 3rd photos, you can see the thread impressions made in the entire hole but primarily in the upper and lower hole segments.
I have attached other photos that clearly show the enlargement of the port side hole. Also included is a photo of the starboard hole with the bolt (hex head shown) inserted that shows a gap forming at that hole.
Additionally, as a side issue that may be affected by the free play issue, but not certain, I have attached a photo with scuff marks from the tire on the inside of the starboard fork. The larger diameter scuff mark aligns with the embossed circular rib on the tire. The smaller diameter scuff mark aligns with the top of the lettering on the tire. There are similar scuff marks on the inside of the port side fork which I did not attach a photo of here. All of these scuff marks have not yet gouged into or removed aluminum material from the forks. If Vans plans revisions of the Nose Fork Assembly (WD-1230) on the RV-12 or any other applicable plane, I recommend increasing the inside fork space dimension.
A bolt with threads that begin outside of the fork area would solve the wear action caused by the threads. But, I think the objective of having bolt threads inside the fork hole width is to ensure available threads to keep the forks from spreading (i.e. confine the forks from spreading and inhibit fatigue). However, the threads are evidently enlarging the hole. There is wear on the bolt thread crest to crest dia. (.367?) in the fork hole area as compared to the thread dia. (.370?) in the section protected by the nut. However, I was surprised to find that the bolt threads crest to crest dia. in the nut area was less than the bolt shank dia. (.373?). This smaller diameter in the threaded area is probably not the major factor causing hole enlargement, but it doesn?t help the problem.
My thinking is to drill and enlarge both holes and insert replaceable bushings in each fork with the port side bushing I.D. being smaller for a drift fit of the lesser dia. bolt threads. I?m thinking that the material for the bushing could be aluminum. Aluminum would entail more frequent replacement, brass would wear less, and steel would last longer but the bolt threads would be susceptible to wear with a steel bushing. If bushings are a viable solution, I'd appreciate the recommended O.D., specific material alloy, recommended hardness, and source for the bushings.
Any fixes or suggestions for this problem are appreciated.
John Richard
As can be seen in the 1st attached photo, the port side hole in the fork has enlarged overall and become oblong (.390?) in the 11:00 & 5:00 o?clock positions as viewed from port side (i.e. 30 degrees aft from vertical). The starboard side hole has some enlargement primarily oblong in the same angle that matches the port side. The enlargement on the starboard side is minor in comparison to the port side hole. This is evidently due to the fact that the crest to crest diameter of the threaded end of the bolt is less than the shank diameter and the wedging action of the steel threads that slices into the softer aluminum. From the 2nd photo and 3rd photos, you can see the thread impressions made in the entire hole but primarily in the upper and lower hole segments.
I have attached other photos that clearly show the enlargement of the port side hole. Also included is a photo of the starboard hole with the bolt (hex head shown) inserted that shows a gap forming at that hole.
Additionally, as a side issue that may be affected by the free play issue, but not certain, I have attached a photo with scuff marks from the tire on the inside of the starboard fork. The larger diameter scuff mark aligns with the embossed circular rib on the tire. The smaller diameter scuff mark aligns with the top of the lettering on the tire. There are similar scuff marks on the inside of the port side fork which I did not attach a photo of here. All of these scuff marks have not yet gouged into or removed aluminum material from the forks. If Vans plans revisions of the Nose Fork Assembly (WD-1230) on the RV-12 or any other applicable plane, I recommend increasing the inside fork space dimension.
A bolt with threads that begin outside of the fork area would solve the wear action caused by the threads. But, I think the objective of having bolt threads inside the fork hole width is to ensure available threads to keep the forks from spreading (i.e. confine the forks from spreading and inhibit fatigue). However, the threads are evidently enlarging the hole. There is wear on the bolt thread crest to crest dia. (.367?) in the fork hole area as compared to the thread dia. (.370?) in the section protected by the nut. However, I was surprised to find that the bolt threads crest to crest dia. in the nut area was less than the bolt shank dia. (.373?). This smaller diameter in the threaded area is probably not the major factor causing hole enlargement, but it doesn?t help the problem.
My thinking is to drill and enlarge both holes and insert replaceable bushings in each fork with the port side bushing I.D. being smaller for a drift fit of the lesser dia. bolt threads. I?m thinking that the material for the bushing could be aluminum. Aluminum would entail more frequent replacement, brass would wear less, and steel would last longer but the bolt threads would be susceptible to wear with a steel bushing. If bushings are a viable solution, I'd appreciate the recommended O.D., specific material alloy, recommended hardness, and source for the bushings.
Any fixes or suggestions for this problem are appreciated.
John Richard
