Mazda and NSU tend to get all the credit for Wankel rotary engines in cars, but Mercedes also did quite a bit of Wankel development, using the motors in SLs as well as in the legendary C111 experimental vehicle you see above. C111s are incredibly rare, and yet somehow, someone on eBay claims to have parts from one of the vehicles’ Wankel engines for sale.
Mercedes first showed the C111 at the Frankfurt Motor Show in 1969 after having begun working on the vehicle in 1967 for the purpose of testing fiberglass car bodies and also for proving out Wankel rotary engines like this one:
Mercedes made a number of different C111 experimental cars; the four-rotor engine you see above came out of the 1970 C111-II, and made 350 horsepower, which was enough to get the car to 62 mph in under five seconds and to a top speed of over 186 mph. But before the C111-II, there was the 1969 C111-I which had a 280 HP three-rotor Wankel engine.
It’s not plainly stated on the Ebay ad which version of Mercedes’ Wankel the $13,600 parts come from, but the seller does say that the rotor and rotor housing were made by Mercedes in Stuttgart in 1971, so chances are, if these are legit, these come from a four-rotor.
I haven’t been able to find any official photos of the C111's engine that show parts looking exactly like those in this listing, but we know that Mercedes made a number of engine revisions during its time developing Wankels, so it seems plausible that someone at the company just snagged some spare parts off a shelf in the ’70s.
I’m curious to know how the seller is sure these come from a C111, and not an SL, which was a key car in Mercedes’ rotary development. According to the company’s press release on the program, the SL received a number of Wankel motors over the years, including a 203 HP “M50F” three-rotor, which powered the W113-generation SL for almost 43,000 test miles between June and October of 1968, and which hit a top speed of almost 130 mph.
In 1971, when these engine parts for sale were allegedly produced, Mercedes spent over two months installing a 277 HP four-rotor engine into an SL. This likely would have taken longer if the R107-generation SL’s transmission and driveshaft tunnel hadn’t been, from the start, “designed to accommodate the greater installed height of the rotary piston engine with its high central power take-off” according to Mercedes.
But the company says there are none of the original rotary-powered SLs in existence, even though Felix Wankel’s R107—which he had outfitted with a Mercedes four-rotor—is still around. And there aren’t many C111s left either, partly because not many were produced, since Mercedes canceled the program in 1971, in part, because of safety disadvantages of a fiberglass body.
As for why the Wankel engine didn’t catch on, Mercedes says durability was a factor, but according to engine developer Kurt Obländer, the issue had more to do with efficiency, saying in a Mercedes press release that the engine type had a “birth defect”:
“the combustion chamber is the central feature of the combustion engine. The priority is to produce an optimum design so as to achieve the most favourable thermodynamic efficiency, i.e. as complete combustion of the fuel as possible. The fact that this did not occur with the Wankel engine, indeed that it could not happen, manifested itself initially in high fuel consumption and later, even more publicly and confirmed officially, in the difficulties in meeting the still quite tame exhaust emission standards for passenger cars due to the high proportion of non-combusted hydrocarbons. It was this birth defect in the Wankel engine, its failure to offer an optimum combustion chamber, which was responsible for its rapid demise and not the constantly repeated suggestions of mechanical problems.”
Anyway, I don’t know if this is a legit Mercedes rotary, or if it came from a C111 specifically, but it seems plausible, and these documents in the listing—which apparently show fabrication instructions for similar parts—have me thinking that maybe this seller, who is based out of Germany, has a hook-up at Mercedes, or perhaps even worked there. It’s hard to know.
I’ve reached out to the seller, and to Mercedes to see if I can confirm that these parts are legit. If they are, then consider me amazed that such a historic piece of automotive history is for sale on eBay for anyone to bid on.