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Citroën M35 – rotary connection

Words: Glen Waddington; pictures: Alex Tapley

In 1969, Citroën unleashed the rotary-powered, hydro-suspended M35 on selected customers for testing

Prominently, it wears a number on the front wing. ‘Prototype Citroën M35 No.417’. That’s 417 out of, er, 267 built. Citroën had planned to produce 500 M35s – each one of them labelled ‘prototype’ – but soon figured it wouldn’t sell them all. This was a highly complex and commensurately expensive small car, after all, with a complicated tale to match. That Citroën left a numeric gap on those wings between 175 and 376 is only the start of it.

I’d spied the M35 first at the Cartier Style et Luxe. You know, that posh concours display on the lawn outside the Duke of Richmond’s place. Sir Jonathan Ive, Nick Mason, Darcey Bussell, Lorenzo Ramaciotti, Marc Newson et al had been deliberating over Peter Neumark’s special-bodied Pininfarina XK120 (see Octane 174), Johnny Bute’s Cadillac 62, Rainer Becker’s Porsche 550 Spyder… and a 1957 Citroën 2CV AZL. Which is a clue. You see, that car, plus a Bijou, a four-wheel-drive 2CV Sahara and this M35 were there to celebrate the 2CV’s 70th anniversary.

Darren Arthur runs The 2CV Shop, and Goodwood PR and fellow Citroënist Gary Axon had persuaded him not only to enter a customer’s 2CV (which scored a class win) but also to transport this highly original M35 all the way up from the South of France, home to 2CV Mehari Club Cassis, the company behind the electric eDen Mehari (see Octane 195) and owner of this car.

But you know the M35, don’t you. Rakish if awkward coupé lines and hydropneumatic suspension make it definitively Citroën, if rather distant from the tin snail. And didn’t it have a Wankel engine? Oh yes. To be clear, it’s the smallest hydropneumatically suspended car ever built. It’s also the first in a very short line of Citroëns to be rotary-powered (we’ll come back to this). Plus, being based on the Ami 8, it can trace its structural lineage right back to the 2CV. So it has certainly earned its place in this class, on this lawn, in this magazine and in history.

From the off, it was going to be a difficult prospect: little-tried technology, in the form of its single-rotor Wankel engine, in a small car priced like a much bigger one, and made available only to select customers, willing to report back on their ownership. Those customers were expected to cover a high annual mileage (a minimum of 30,000km, around 19,000 miles), putting the car to a real-world test. They were offered the little fastback for FF14,120 (it was sold only in France), twice as much as a 2CV cost and on par with the much larger and suaver D Special. A sticker in the rear window translates as ‘This Citroën M35 prototype, fitted with a rotary engine, is undergoing long-term testing at the hands of a Citroën customer.’

Those brave owners were offered a two-year engine warranty plus a loan car if their M35 needed an extended workshop stay. Every service department was asked to make notes when they saw an M35 and to send feedback to Citroën HQ. There was also a quick-response technical support service, as there had been when the DS was launched, 14 years before, with its newfangled suspension. Oh, and that same hydropneumatic system featured here, too. Citroën was no stranger to complexity.

Having said that, one of the rotary engine’s strengths was its relative paucity of moving parts: it was compact, smooth-running and powerful for its size. Pierre Bercot, Citroën’s MD and chairman from 1958 to 1970, thought it looked like the future and signed up to a joint venture called Comobile with NSU in 1964. A joint engine manufacturing company, called Comotor, followed in 1967, with a factory in Germany, close to the Luxembourg border. The M35 arrived in 1969, the same year as Mazda’s R130 Luce, preceded only by NSU’s Wankel Spider (from 1964, the first rotary-powered car to go on sale) and its 1967 Ro80, and Mazda’s Cosmo 110S (also from 1967).

Dr Felix Wankel had begun developing engines for NSU in the 1950s, and NSU subsequently sold licences to other manufacturers, including Alfa Romeo, Ford, GM, Mercedes-Benz, Nissan, Porsche, Rolls-Royce, Suzuki and Toyota. US firm Curtiss-Wright developed larger versions for use in aerospace, but only NSU, Mazda and Citroën got very far at all with production cars. Famously, Mercedes developed the C-111 supercar, which scored some speed and endurance records though remained very much an object of fantasy, and in Octane 176 we featured GM’s rather fabulous stillborn Corvette Two Rotor.

Mazda pursued the technology for longest. Its triple-rotor Renesis engine powered the RX-8 right up to 2012, and won the International Engine of the Year award in 2003, Mazda’s engineers having conquered the Wankel’s infamously rough low-speed running (due more to controlling fuel delivery than overcoming inherent imbalance) and its notorious rotor-tip seal issues. The latter drove NSU into the arms of Audi in 1969, largely as a result of offering a replacement engine every time one broke down, though the engines weren’t quite as fragile as legend would suggest. Many of those failures to proceed were as the result of fouled sparkplugs, caused when owners, confused by the Ro80’s semi-auto torque convertor transmission, drove everywhere in top gear, failing to let the rotary sing as it needed to. And the huge costs of developing and building the engine, even with support from Citroën, didn’t help. Those costs also contributed to Citroën’s acquisition by Peugeot in 1974.

Enough of that. What about the M35? Well, it looks like an Ami, granted, though parts are interchangeable only ahead of the A-pillars, and even the grille and its badge are specific. The windscreen is unique, which must have pleased those 267 early adopters, and while the rear wings look like those of an Ami Service van, they’re shorter, and the doors are longer. Equally, the roof, side glazing and bootlid are shared with no other car. All of which might come as less of a surprise when you learn that assembly was outsourced to coachbuilder Heuliez.

The engine we know about, but the Ami’s 2CV-style underpinnings were also heavily adapted, in order to take a version of the DS’s hydropneumatic suspension system, though the brakes and steering are conventional. The four-speed manual gearbox later saw service in the GS, which arrived in 1970, and lessons learned with the M35’s suspension were applied there too. Inside, the main dash moulding is as per Ami, though there’s a revcounter mounted in a pod to the left of the strip speedo and characteristic single-spoke wheel – with a 7000rpm recommended rev limit, it’s rather more necessary here than in a 602cc flat-twin Ami 8. SM owners might recognise the front seats, though here they’re trimmed in vinyl rather than nylon plush.

The ignition switch is below the hub of the steering wheel; twisting it winds the Wankel gradually into life, whereupon it drops into a rather two-stroke-like phutt-phutt ring-a-ding idle – different from the blat-blat of an Ami 8, though not necessarily any more refined. Until you rev it. Once it’s spinning past 3000rpm or so, it sounds less mechanical, more jet-like, and is suddenly
a world away from the 2CV’s jackhammer noisings-off.

Give the engine a few seconds to pump up the suspension and the M35 rises camel-like, then select first via the dash-mounted in/out lever. Some revs, pull away and you’ll sproing along the road, that soundtrack calling to mind a 1970s hairdryer. Well, to my mind, anyway.

It’s not exactly quick, although 49bhp feels faster than you might expect, possibly because of the rotary’s liking for revs – it’s a fair bit more than the Ami 8’s 32bhp, at any rate. And you get to luxuriate in a ride that is uncommonly supple for a small car. Not just soft but absorbent, with the sense that you’re travelling over a surface rather than through it. Sure, any old 2CV will get you across a ploughed field without breaking eggs, but it can still make an undulating British road feel like a boiling sea. There’s none of that here; instead, you get much of the poise and maturity you’d enjoy in a DS, and that’s remarkable for such a light car. The M35 might be compact, but it’s rare-groove and feels unlike much else you could possibly buy. Those 267 owners were certainly courageous, and the M35 wasn’t cheap, but what an opportunity: to own what amounts to a prototype, and be involved in showcasing the latest technology.

So what happened when Citroën’s experiment came to an end, in 1971? Well, the company didn’t want to bear the cost of providing back-up for the cars, so it offered owners a generous trade-in on a new alternative, which most took up – not surprising, given that few of the rotary engines got past 40,000 miles without needing a rebuild. Tragically, the returned M35s were scrapped, though it’s reckoned that about 100 escaped the crusher. Those who kept their car had to sign an agreement that Citroën would not have to stock spare parts for them. They’d been brave to buy them, and were even braver keeping them.

Still, Citroën forged ahead. A compact family car with hydro suspension and a rotary engine certainly sounds appealing, and the Ro80 had proved how well the Wankel suited a larger, more luxurious car. The CX would have had a triple-rotor engine had early plans come to pass, but first came the GS Birotor, its engine with twice the M35’s modest 497.5cc swept capacity (though it was rated as 995cc, given that it made power on every stroke, twice what a reciprocating four-stroke manages). It landed in 1973. As did the oil crisis. Wankels are thirsty, and a great what-might-have-been suddenly wasn’t. Only 873 Birotors were built, and Citroën turned its back on rotary engines for good. The buy-back and crush scheme was put in place again, and similarly – thankfully – there were escapees.

Thus ended a brief window in French automotive history. Next time you giggle at the wobbly progress of a 2CV or Ami 8, just remember the M35, and how far ingenuity took those proletarian underpinnings.  

Factfile – 1971 Citroën M35

Engine 497.5cc single-rotor Wankel (rated at 995cc), Solex carburettor  Power 49bhp @ 5500rpm  Torque 50lb ft @ 2745rpm  Transmission Four-speed manual, front-wheel drive  Steering Rack and pinion  Suspension Front and rear: self-levelling hydropneumatic spring/damping system. Leading and trailing arms respectively  Brakes Inboard discs front, drums rear 
Weight 815kg  Top speed 90mph  0-62mph 19sec

This article was originally published in Octane 206, August 2020

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