TD axel to gear leg fit

[n502pd]

I will be installing my axels to gear legs sometime in the near future. there has been chatting elsewhere about wheel shimmy and holes being elongated on the axel tube. Does anyone here have suggestions on how tight a fit onto the geare leg the axel tube needs to be? And, what torque value should be used , if different from values in AC 43.13 It is the tightness of the fit I am needing most! Thanks! :)

[N111YX]

Joe, I think the key for a tight fit is updrilling in multiple sizes and maybe even a reamer at the end if you really want it tight. However, I don't think most of the shimmy problems are the result of loose axles but rather improper alignment. There are techniques on this site that show ways to achieve great alignment the first time...

viewtopic.php?f=33&t=126

[n502pd]

Thanks for the quick reply, Kip! I do understand that the bolts must/should be almost an interference fit. I was really asking about the fit of the 4130 cormolly tube that slides over the gear leg, thru both of which one drills the aforementioned bolt holes. Yes for sure allignment can cause shimmy. Some have indicated that after the shimmy they have noticed the hole in the 4130 steel to be elongated. Some reweld the hole and redrill, others appear to upsize the bolt. I have read a while ago that others get a really tight fit using shims of some type between the gear legs and the 4130 tube. Maybe they have to tap the axel assembly on with the shims...I dont know. lastly, I was asking about the actual torque they used for the bolt. I will look at you suggestion info point. Other than you, I received NADA from that other group. Huh. Thanks again!!

[N111YX]

Joe, I see what you are referring to now but I still don't think that's the major cause of shimmy. My legs "float" a bit in the engine mount tubes but after 550+ landings I only get shimmy with brake application because the Azusa wheel castings are so poorly made, despite the use of the Sonex machined wheel drums. The Sonex drums make the Asuza's tolerable in my opinion but just barely. In fact, I just changed my brake drums out and at the moment, I am nearly shimmy-free except for brake application between about 15-25 mph. Above and below that is fine. As the drums wear, it may get better or worse. Lot's of mysteries here, I know.
Tire pressure seems to have an effect on shimmy too as the tires leak down over the course of a few weeks there may be a combination of pressures that change the geometry of alignment enough to get some shimmy. Someone else who has had more of a shimmy problem may want to chime in here on what their fix was...:)

[falvarez]

Hi Kip....I have a quick follow up to what you mentioned about the legs "floating" in the engine mount tube that I'm hoping you can confirm...

The top of my gear where the bolt is, is quite snug and because we used drilled bolts w/ castellated nuts, I don't have much torque on the bolt...my assumption is Sonex wants it that way or they wouldn't have mandated drilled bolts. Where the gear exits the lower fuse, there is some play. I thought Sonex has made comments in the past that the leg is supposed to be free to rotate there in order to help absorb the landing stresses. I have heard of some folks putting metal shims in there to tighten up the fit, but that seems to contradict the purpose of it...can you confirm that you did NOT put any shims in the lower mount to tighten the fit of the gear leg?

Also, Joe...when I put my axle on the gear leg, even though I feel I did a good job with the drilling, I found that there was some play (not the bolt hole...the axle tube was a bigger than the gear leg)...I could easily see this becoming an source of elongating the hold in the steel tube. If you have this similar issue in the axle, I would recommend using shims stock or something else to remove all play in the axle completely....but as you can see above, I'm still unclear if we should be removing any play in the engine mount.

[kmacht]

A fellow sonex builder indicated to me that after some time flying the hole that attaches the axle to the gear leg had elongated on his Sonex. He simply welded a washer to the outside of the gear leg formed to the round surface of the axle tube and re-drilled the holes through the washer to fit the bolt essentially doubling the wall thickness of the tube in that area. If you look at how thin the tube is and the forces that are being delvered to that bolt hole it only makes sense that over time it is going to move and oval. I did mine proacivly as I was already welding on the axle tube to add the tracy-obrien backing plate. The washer trick is also a great fix if you somehow mis-drill the alignment of your axles.

Keith

[N111YX]

Frank, I do not use any shims on the gear legs anywhere and as of now, I see no need for them based on my experience...

Hi Kip....I have a quick follow up to what you mentioned about the legs "floating" in the engine mount tube that I'm hoping you can confirm...

The top of my gear where the bolt is, is quite snug and because we used drilled bolts w/ castellated nuts, I don't have much torque on the bolt...my assumption is Sonex wants it that way or they wouldn't have mandated drilled bolts. Where the gear exits the lower fuse, there is some play. I thought Sonex has made comments in the past that the leg is supposed to be free to rotate there in order to help absorb the landing stresses. I have heard of some folks putting metal shims in there to tighten up the fit, but that seems to contradict the purpose of it...can you confirm that you did NOT put any shims in the lower mount to tighten the fit of the gear leg?

Also, Joe...when I put my axle on the gear leg, even though I feel I did a good job with the drilling, I found that there was some play (not the bolt hole...the axle tube was a bigger than the gear leg)...I could easily see this becoming an source of elongating the hold in the steel tube. If you have this similar issue in the axle, I would recommend using shims stock or something else to remove all play in the axle completely....but as you can see above, I'm still unclear if we should be removing any play in the engine mount.

[n502pd]

Thanks to everyone for the replies. I do like the proactive hint about the washers on the axel assembly, and since I have not installed anything yet, I may just do that too. I also like the idea of shimming for a tight fit at the axel, and will probably do that too. The engine mount shim I am not so sure of for the same reasons given...shock absorbson thru gear leg flex and twist(?). maybe i should also run this by Kerry to see what he says.

About the sonex upgraded brake drums...do you feel it is worth while dto do that upgrade or stay with the original drums?

Thanks all!

[kmacht]

If you are going to put any money into the brakes I would suggest going eithe with the new sonex hydraulic setup or the tracy-obrien setup. The machined brake drums are already $200 just for the drums and they still have some of the same problem as the machined brake drums. If your wheels don't run perfectly true you will get rubbing and jerky braking. For $450 you can get the aeroconversion brake kit which no long counts on the drum running true. If the disc is slightly off the pad will float with it. If you are comfortable doing some welding and don't mine welding a backing plate on your axles you can go with the tracy-obrien C-90 brakes and stick grip master cylinder for about $385. Their brakes float on 3 pins and will take care of any axial as well as radial mis-alignment of the wheels.

Keith

[n502pd]

Thanks Keith! I am inclined to do just that, but for the first little bit I need to keep cost as low as possible, and after I get a few hours on the plane, I probably will put better brakes on. I have no trouble welding. Juice brakes are at the moment more mony that I can affort, but I do understand that they do illiminate all that has been discussed. All this info is great to have! Thanks again for the input!