Not sure if what became the FMR500 engine had a prior incarnation to the agricultural use it was put to but it appeared as supplied to the Cultimax farm/small holding machine before the Schmitt was thought of. So in other words a tractor engine in a similar way to the TR2. Both sets of owners are more than happy to deflect this information but it makes nothing less of the car itself, only any assumed status that never existed. Both cars records stand for themselves as pretty rugged performers.
Allegedly Sachs were well aware of the engines shortcomings and probably had misgivings about the number of units Fend would sell into the bargain, despite the success of the KR200 which owed much to Sachs tweaking their unit to suit the car. They chose not to manufacturer the engine but offered the construction rights. FMR had no prior experience of making an engine but bereft of a suitable engine that another manufacturer would supply they bought the rights to the 500 twin and made it. Clearly with no control to the product Sachs wanted to distance themselves from what was, for them, an out dated design. It is on this basis that the FMR500 engine is not the easiest thing to live with as it is made with some quality control issues and is a bit of a one off. That it was used to achieve some very good competition results and that the hard core owners make these units reliable says something for the design, which is undoubtedly flawed. What would have happened if money had been spent on it so it had a gearbox of the quality of, say, the Goggo, who knows. It would certainly have been even quicker over the ground. Difficult to know if it would have sold many more as it would have had to have been even more expensive.
The TG500 appeal is all rolled up with this engine thing. So much of the car was a cul de sac of automotive design in hindsight yet it works and works better than it should do. There will never be another car like it. It is that rare thing a successful failure and you cannot help but feel for it on some level.