Here's one more bit of useful information about the BMW 650cc single that perhaps puts into context the skepticism of Heiri's BMW buddies about Loncin's manufacturing of the engine. According to this wikipedia entry, the 650 single engine indeed is assembled by Loncin with technology from Rotax of Austria, which had made the engines previously, and even the Loncin-manufactured engines contain some components provided by Rotax.

2009: G650GS

In late 2008, BMW relaunched the original single-cylinder F650GS under the new name G650GS in the United States, South America, Greece[1] and Australia.[4][6] The new G650GS is essentially the 2007 single-cylinder F650GS brought back into production with some minor modifications and with the engine assembled by Loncin in China instead of Rotax in Austria, but still using parts manufactured by Rotax in Europe.[1][7][8] The finished engines are shipped back to BMW in Germany where the bikes are assembled. G650GS models with the Chinese-assembled engines can be easily identified as the engines are painted black while in the earlier European-assembled engines were finished in silver. For a short period prior to discontinuation of the bike in 2007 the engines were assembled by Kymco in Taiwan.
The G650GS received some upgrades over the F650GS of 2007: the engine now produces 3 additional horsepower (now 53 hp) and received a stronger 400 watt alternator.[1] In the United States and Australia, ABS and heated grips are now standard equipment instead of additional cost options.[1] An emergency services specific version of the G 650GS, fitted with blue lights and sirens, is available from BMW Motorrad's Official and special duty vehicles division.[9]
In 2010, at the EICMA show in Italy, BMW Motorrad announced the global availability of the G650GS with a slightly down-rated engine producing 35 kW (47 hp).[10][11]

BMW has only itself to blame for the confusion, since they changed the model name of the 650cc single from F650GS to G650GS, then started using the F650GS name for the new parallel twin bike that was launched in 2009 along with the F800GS. To add to the confusion, the F650GS is not even a 650cc engine, but a 798cc (i.e., "800cc") engine that is essentially the same engine as that in the F800GS! Why, oh why, couldn't they just keep using the F650GS name for the thumper, and come up with something new for the new twin. And why, oh why, did BMW think it necessary to build two separate bikes around the new 800cc parallel twin engine -- one designated as an 800 and the other designated as a 650??? These guys may be marketing geniuses, but they are not particularly honest with their customers.

dang.