TG500 Engine Development History

Fend started negotiations with Fichtel & Sachs to buy the rights to produce an engine developed by them for the burgeoning small car market in Germany. It is thought they had originally designed this engine type during the war as a starter motor for large aircraft engines. An existing drawing dated 16th December 1955 that shows a Tg type engine design and two well know experts, Hans Friesnig and Dr.Norbert Mylius, believe that the Austrian Rotax company, (well known for two-stroke engines), had an interest in the design. This new design now included a gearbox and differential and was made from components manufactured by various sub-contractors and assembled by FMR. The engine castings were produced from sand mouldings and each required considerable amount of machining to establish flat and square faces to match the two halves. They are generally of inferior quality to the Sachs 200 castings and are often full of blowholes that break through as the casting is machined. As much as two millimetres had to be removed and this could affect the position of the cylinder base relative to the crankshaft. On two stroke engines, even small variations in these dimensions can result in noticeable differences in performance as the port timing is affected. The two crankcase halves are line bored together to give correct dimensional tolerances. Thus each engine is hand built and unique ? a feature normally found only on exotic cars such as Aston-Martin. Unlike the Sachs 200 engine, the tolerance variations do not always allow different crankcase halves to be interchanged. This makes repairs to the crankcases especially difficult in the case of damage caused by a big-end bearing failure. Tg?s always had a bad reputation for oil leaks, a common feature because of these casting defects. Great care is necessary when re-building the engine to make sure everything is properly sealed.

Ingineur Adeuard Ernst was responsible for development of the engine within FMR and local manufacture of components in small batches meant that specials could be made to suit specific requirements. Ernst made many tests personally and developed the Tg for competition. Eventually he became frustrated with developing Tg?s for other people and asked Fend if he could have a Tg for himself. This car was built from components especially for competitive use and did not have the ?portholes? in the rear engine covers that are a feature of all Tg?s. There was no upholstery and a ?sport? type top was fitted with the characteristic racing type half screen. This is believed to be the only known example of a Tg with the ?sport? top. Now owned by MOC member Colin Archer, this car is finished in distinctive metallic red and silver paint that is believed to be 1950?s BMW colours. Colin has gone to a lot of trouble to restore the car to original external appearance. He even traced the original ?sport? top to renowned German Messerschmitter, Bernd K?gler. Careful negotiations eventually re-united the original top with the Tg.

Particular attention was given to Tg gearboxes where many different ratios were produced to suit the various competitive events the Tg took part in. These were never offered publicly and only those supported by the factory had access to such special services. Some came to Britain and Ken Piper demonstrated their effectiveness very well in the various Tg?s he entered competitively. Another competitive driver by the name of Hans Wiesnet demonstrated his considerable driving skills in regularly beating Fritz Fend in driving events. Hans was deeply involved with the Messerschmitt from the beginning particularly with developing the KR175 and he owned the ninth KR175 to be produced. Tg owners today are much better served thanks to the efforts of Heiko Zimmermann. The crankshaft he helped to develop is significantly stronger than the original and is less prone to catastrophic failure. Another interesting discovery is the variation in ignition timing caused by the crankshaft deflection under load. This causes some variation in the ignition timing that can be avoided by fitting electronic systems using sensors rather than a crankshaft mounted cam with contact breakers. However, the Tg engine remains a temperamental beast requiring special care to avoid piston seizure and other engine damage. Bert Grimmer is developing a freewheel system for the Tg that will avoid the shuddering effect of the engine and transmission during over-run. This system was used on other two-strokes such as DKW and Trabant. Two strokes have little engine braking and smoothness is improved considerably with this device. MOC member Russel Church has arranged manufacture of new cylinder heads to correct a well known Tg weakness with blown head gaskets. These dedicated people are continuing to develop this engine, completing the work that FMR should have done!