Gearbox lubrication and gear oil selection

Jumping out of 4th gear is not unusual for the Sachs 200 engine as most shifting is done between third and fourth when on the open road. This was always a difficult problem to solve and there were cases that even the factory mechanics could not cure. However, it is not common for the other gears to jump out of their selected positions into the adjacent neutral point. If this happens, double check the oil level in the gearbox. Use the clutch inspection cover to verify the oil level – it should be level with the bottom of the clutch inspection aperture.

Good lubrication is vital part in preventing gearbox wear. If the clutch inspection cover is used as the oil level, you can be certain that there will always be sufficient oil. Oil should start to run out of the cover when it is removed on level ground and normally about 800ml of SAE 90 gear oil is required for a complete oil change. If the oil level is too low, the first clue is often jumping gears. If you have a worn gearbox, things can be improved by using a SAE 140 oil and I have also had good results from 85W140 multigrade oil from Wal-Mart stores in the USA. There are many oils available today that are marketed for use with limited slip differentials. Many of these have ‘clutch’ plates similar to the Sachs design. These higher viscosity oils are often used in agricultural applications and you should try your nearest tractor dealer in case of difficulty. However, it is essential that these gearbox lubricants are compatible with friction clutches running in oil and you are usually safe with oils marked for limited slip differential use. Lubricants marked as EP or Hypoid that do not mention compatibility with limited slip differentials, will destroy the clutch. If you have a worn and excessively noisy gearbox, try using 140 grade oil that is intended for steering boxes. This works well and I have used it for over 30 years. There is no noticeable difference in operation unless you use your Messerschmitt at very low (freezing) temperatures when it can create some clutch drag during a cold start.

Unfortunately, there were some errors in the engine manual that resulted in use of the level plug on the clutch housing to determine the oil level. This level may have been acceptable when used in motorcycle applications where the engine has less weight to pull and less heat from the clutch operation. Do not touch this level screw! It normally strips when removed and you will have to remove the entire clutch housing to repair it.

In the KR200, the clutch housing and primary chain operates as an oil pump to feed oil back into the gears through an ingeniously designed duct system. Oil is picked up by the chain and thrown off by centrifugal force into the gearbox feed duct. This can only work effectively if there is enough oil in the gearbox. Check the parts manual and make sure your engine has the oil thrower ring and diverter casting in position. This is often damaged when the primary chain is badly worn and makes contact with the aluminium diverter casting. Some previous owner may have left this part off following an overhaul. It does not affect the operation of the gearbox but does limit the effectiveness of the lubrication.