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Touring Motor Gliders Association (TMGA)

Tailwheel Replacement

Steve Sliwa

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We have found replacing the tire and inner tube of the standard tailwheel to be problematic for our local shop. Seems like the inner tube gets some damage after all of the wrangling. Talking to our IA we were thinking that going to split rim replacement might make life easier. Has anyone else considered or accomplished this:


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Did they baby powder the outside of the tube and inside of the tire before assembly? This helps a bunch if it's a tight fit because it dramatically reduces friction between the tire and tube. A little bit of air in the tube will also help. Just enough for it to keep it's shape.

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I have done it several times. Used also baby powder but you have to put the wheel over a round rod and fix the rod into a wise firmly. Then you have enough support to push one side of the tire deep enough into the rim to get the other side over

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  • 7 years later...


1) The stock wheel is a bear to work with. In my experience, the key is to first support the wheel via a dummy axle post (secured rigidly in a workshop vise) and work one tire bead onto the wheel; then work the tube into the tire, then mechanically clamp (i.e. squeeze without pinching the tube) one sector of the tire together so that both tire beads can be worked together down into the "valley" at the mid-plane of the wheel, and then work the remainder of the second bead onto the tire. Talcum powder does help. Liquid soap can also be used, but expect a mess. It's hard enough to do in the workshop and quite impractical if you're stranded somewhere.

2) As HiFlite has pointed out, the Tost Moritz II is well worth using. This is a two-piece split wheel that allows easy tire/tube replacement. A spare tire and tube, plus a few basic hand tools, are all that are needed in the aircraft to avoid being stranded. I can confirm HiFlite's information that there is a small difference in the hub width (and thus bearing spacing) of the two wheel types, which necessitates some adjustments to the spacers. Specifically, the Tost wheel is slightly wider than the stock wheel and so, if the stock shoulder spacers are placed into the Tost bearings, the overall spacer-to-spacer distance ends up slightly larger than the gap between the fork legs and it won't fit. There are a couple of ways to deal with this: 

(a) Place the stock spacers in a lathe and turn off a millimeter or so (sometimes a fraction of a millimeter or so) from the inside shoulder of each spacer. To figure out how much material to remove, place the stock shoulder spacers into the Tost wheel, measure outside-to-outside across the spacers, and compare with a measurement taken inside-to-inside between the fork legs. Take the difference between the two measurements and use half the value for the amount of material to remove from under each shoulder. One consideration (issue) with this method is that the hollow spacer tube (between bearings) of the Tost wheel has a 12mm bore, whereas the hollow spacer tube between the bearings in the stock wheel has a 6mm bore (in order to fit the 6mm axle bolt). Re-using the stock spacer tube (compression tube), by transferring it over to the Tost wheel, won't work because it'll be too short and using the included Tost spacer tube is questionable because there won't be anything to hold it concentric with the 6mm axle (i.e. not a good idea to allow the Tost hollow spacer tube to orbit the axle). A new spacer tube (with length equal to the Tost spacer tube and bore matching the stock tube) can be turned on the lathe. Alternately, a sleeve (with 6mm ID and 12mm OD) could be inserted into the Tost spacer tube. 

(b) Another option is to order a pair of FTCLA flanged collars from Misumi. This is a "configurable" part and dimensions can be specified as needed to fit the requirements. For example, a configured part number might be FTCLA-V6-D12-H15.5-T13-L30. https://us.misumi-ec.com/vona2/detail/110300235050/ . The V6 corresponds to the axle bolt hole size, the D12 corresponds to the bearing ID, the H15.5 is the shoulder OD, the T13 is the shoulder length (this is the value that needs to be determined according to the fork spacing), and the L30 is the overall length. The length of the shank that goes though the bearing and into the hollow compression tube between bearings is thus 30mm - 13mm = 17mm. Note that the L30 can be any reasonable number, just not too long otherwise the shanks of the two opposing spacers will meet at the middle of the wheel assembly. The main benefit of having the shank length greater than the bearing width (8mm) is that the extended shank will extend past the bearing and hold the 12mm ID Tost spacer tube concentric with the 6mm axle (avoiding the issue noted in the previous paragraph). The shank length can be made any length up to a value that is shy of the two shoulder spacers meeting in the middle of the wheel assembly. Since the shoulder length (T13 in the example) can only be specified in 1mm increments, generally round the required dimension down to the nearest millimeter (or if the required value is really close to the next larger increment, round up and a tiny amount of flex in the fork legs will accommodate it). It is also possible to specify one part with a shoulder length one millimeter more than the other (for example, order one with T13 and the other with T14). Note: the stock spacers are not necessarily identical either. For any fine-tuning of the shoulder-to-shoulder distance, some 0.2mm, 0.3mm, or 0.5mm thick stainless steel ring shims from Misumi can also be considered. For example, PACK10-CIMRS12-16-0.2, PACK10-CIMRS12-16-0.3, or PACK10-CIMRS12-16-0.5. https://us.misumi-ec.com/vona2/detail/110302677870/ .

Cheers, Leo



Tost Moritz II wheel with shoulder spacers.


Side-by-side of Tost two-piece wheel with stock single-piece wheel.


Close up of slightly shorter shoulder spacer (placed inverted) next to the installed stock spacer.

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