BMW’s new R18 big boxer engine

MIRAMAS, FRANCE—A big-ass Boxer. That’s what Beemerphiles have been asking BMW to make for ages. A big, staunching, horizontally opposed twin with pistons the size of Bavarian beer steins. Liquid cooling? That sorcery is for technophiles. And pushrods. It had to have pushrods.

To hell with all this double overhead cam, variable-valve timing mumbo-jumbo. Give us good old-fashioned, reciprocating tubes, and make sure they’re placed atop the cylinders like the they were on the boxers of the mid 20^th Century so we can marvel at their unsophisticated simplicity.

Actually, no one really asked for such a machine, but BMW went and built one anyway. The R18 is BMW’s newest platform, and it’s a cruiser that harks back to simpler mechanical times. Its “Big Boxer” engine is designed to emulate the art deco exterior of the 1936 R5 boxer engine, but with modern internals. Except the pushrods – those are old school.

Dissecting the R18

I got an exclusive look at the R18’s innards, as well as the inner workings of how BMW designs and tests bikes (That story will be published here soon – Ed.), at BMW’s Miramas Proving Grounds, located here in the south of France.

Aside from the engine’s smooth, rounded crankcase, gearbox and engine covers, other design elements that tie this upcoming new cruiser to BMW’s past include an exposed, nickel-plated drive shaft, and a unique rear drive unit that is incorporated into the swingarm, à la 1936 R5.

Inside the engine are 107 mm pistons that travel 100 mm in their bores, producing a total displacement of 1,802 cc. Piston skirts are impregnated with an anti-friction coating, and because of its large size, the plain-bearing crankshaft has a third bearing journal between the crankpins for added support, unlike the twin main journals of all other boxers. Output is a modest 90 horsepower, but torque is a more substantial 117 lb.-ft., peaking at just 3,000 rpm. Redline is at a car-like 5,750 rpm.

Air and oil cooling (jets of oil cool the underside of the pistons) mandated a rather low compression ratio of 9.6:1 (via a dished piston), and to further reduce the likelihood of detonation there are two sparkplugs per cylinder. Despite these knock-reducing measures, the engine requires premium fuel.

There are two chain-driven camshafts within the vertically split crankcase, and the pushrods operate four valves per cylinder via rocker arms. The tappet rollers are solid, therefore the valves need occasional adjustment, via screw-and-locknut adjusters on the rocker arms — so this should be an easy and inexpensive bit of maintenance.

What isn’t here

On display for me to inspect was a completely disassembled R18 engine and gearbox that had endured the equivalent of 100,000 km of testing on a dyno. While some wear was evident on bearings and pistons, to my experienced eye it seemed negligible.

Two things were missing from the parts on display: a counterbalancer, because there is none, and a clutch. There is a balancer incorporated into one of the cams to reduce low-frequency shaking, which should produce “good vibrations,” at least according to the technical presentation. I was told the clutch was missing because it had been returned to the supplier for analysis.

Just like the pre-liquid-cooled boxers produced before 2012, the R18 utilises a single-plate dry clutch. BMW’s engineers mentioned that the clutch incorporated an anti-hopping function, which when translated means it’s a slipper clutch. This is a unique design – I’ve never before heard of a dry, single-plate slipper clutch – so I asked about it. The engineers looked at each other, smiled, and replied they could not yet talk about it, though they did confirm it is a mechanical system. Gone for analysis… right.

Behind the clutch is a separate six-speed gearbox. Between the gearbox and engine, on the left side of the engine, is a small lever. This lever actuates the optional electric reverse gear, which is powered by a separate motor, not the starter.

A rolling chassis was present, and it uses a large, conventional twin-downtube steel frame. A massive triangulated swingarm pivots at the bottom, with a single, horizontal shock mounted up top, without linkages. Unlike all other current BMW Boxers that use a Paralever system to counter drive-shaft jacking, the R18 has a linkage-free swingarm that uses chassis geometry to counter it.

I saw it

While I got a very detailed look at the engine and chassis of the R18, there were no complete bikes on hand — at least there weren’t supposed to be any. The bike will be going into production in the first quarter of next year, and will probably be at dealers by mid-summer as a 2021 model. BMW has only shown a pair of concepts to date, the R18 and the R18/2, with no indication of what the production bike will look like.

Well, I got an unintended glimpse of an early prototype. It rode right by me during lunch, which was held outdoors with a view of the high-speed test track around the perimeter of the proving grounds. As I stood outside post-sandwich, I saw a black bike with a wide handlebar and big round headlight approaching along a narrow access road that went right by where I was standing. I immediately recognised it as an R18 model.

My hosts here tried to pull me away to keep my eyes from prying, but pry they did: my 15-second glimpse revealed a long, low, slick-looking cruiser with a very low solo saddle and mid-mounted footpegs, and low-slung dual mufflers finished in inverted fishtail tips, just like the 1936 R5. A long, black fuel tank had kneepads, and the bike emitted a characteristic boxer drone, albeit with a deep, rich bellow of a tone.

The bike more resembled the R18 concept than the more contemporarily styled R18/2, but it had a unique design, and looked more refined than either of those one-off concepts.

The commotion I caused was harmless, though I was later told that test riders had a meeting the day before, and were advised that no testing was to take place while we were there. Security folk were trying to identify the test rider while I was there, hopefully only to scold. I was also told that there were actually a half-dozen test bikes on the premises, but they had been put away in one of the workshops, out of sight — well, all but one.