Converting your KR200 to 10mm wheel nuts

When Fend first designed the Messerschmitt he followed the training of his years in aircraft engineering and made the rear wheel studs just strong enough for the job. This did not take account of the different torque settings, worn nuts, and just plain incompetence by owners. The result was that 8mm studs used on the rear wheel fail with alarming frequency. Wheel assemblies are also prone to metal fatigue. Kabinews readers have been warned frequently in recent years about the consequences of sudden, catastrophic failure of the rear wheel. MOC offers a new wheel designed to cope with everyday driving but this is offered with 10mm stud holes to suit cars built after 1959. To use this stronger wheel assembly, the rear axle must be modified using the following procedure published by Heiko Zimmerman in a recent edition of the German magazine, KaroNachrichten. If you are not sure about any of the engineering terms and procedures described, do not attempt this job. Remember, the rear axle is a crucial safety item!

Following information from a club member, who had the spare wheel fly off, the following information is offered for the correct way of fitting the wheel studs to the real axle. The procedure is principally the same for front and rear except for the dismantling of the rear axle 1411 (early) and 1771 (late) For this objective it is essentially more complicated than the dismantling of the front hub. Unfortunately, the larger studs are much more important on the rear axle than they are on the front.

The old wheel studs with 8mm thread are often threaded through the flange of the rear hub. That is the hub is tapped (M8) to accept the studs. So that they will not come undone when the wheel nuts are tightened, one flat of the hexagon head on the early kr200 is retained by a welded steel cover that is prevented from turning by a cap head screw. The later ones were simply welded into place. The change procedure is as follows:

1. Steel cover/welded point should be ground away with an angle grinder. IMPORTANT: make sure you do not damage the shaft seal area of the shaft where the shaft seal runs.
2. Unscrew the wheel studs from the back. Sometimes this can be easier if you cut off the threads before removing the bolt. Of course you can also grind off the complete hexagon head and take the stud out from the front, but with this method everything is very warm and it is possible to damage the working surfaces of the shaft.
3. The tapped holes should now be opened out to 8.5mm and countersunk both sides.
4. With M10 taps (these should be in three stages: first, second and plug taps), cut a new thread into the flange face. CAUTION: the axle shaft is made of high quality steel and so you should lubricate well during each cutting with the tap and after each turn, turn half a turn back to break off the swarf.
5. The new wheel studs to the best of my knowledge are not available with the required 2mm head and so you must turn the head of a standard bolt of 30mm length. They should be high tensile bolts marked 8.8. These should then be threaded into the tapped holes from the rear and screwed in really firmly. All four studs must be vertical to the flange face.
6. Weld one of the hexagon flats of each screw to the flange (with a MIG welder). IMPORTANT: The rear axle shaft bearing surfaces and the oil seal surfaces should be protected during the welding operation against splatter. Clean up the welds with a grinder so that the clearance is maintained to the brake shoes.
7. Now the brake drums must be modified and opened out to 10.5mm diameter to accept the new studs.

PS. For those who want to avoid the procedure on the front axles will have the problem that the rear wheel will need to have 10.5mm holes for the rear axle stud. That will not fit very well on the front axles on the 8mm studs of the front hubs. In one of the Messerschmitts that I bought many years ago (that is one that cost only DM50, driveable, and with T?V (MOT) naturally!) I discovered that the spare wheel had 8 holes four of 8.5mm and four of 10.5mm; also not bad!