Yamaha’s New Twin

Latest addition to “crossplane” engine family has two cylinders.

Yamaha

Yamaha recently showed two engines at a Tokyo "business briefing." One was the new FZ-09 Triple we have previously described. The other was a basic but fair-sized, liquid-cooled parallel-Twin. Because the engine is part of Yamaha's "crossplane" family, we can guess that its crankpins are set at 270 degrees like those of the earlier TDM850/900. This gives a pleasing syncopation to the exhaust sound, making it quite distinct from the flat drone of a classic British Twin.

Inclined forward 10 degrees, the cylinders are cast in unit with the upper crankcase. What is surely a balance shaft housing projects from the front of the case. In one of the views of this engine, a card on the stand begins “90 x 71.” If these numbers are the bore and stroke, they make this Twin a hefty 903cc, which is consistent with the very large butterfly throttle bodies on the rear of the head. Only two injectors are used, located downstream of the butterflies. The throttle shaft carries a pulley made for dual cable operation; no ride-by-wire here.

A look at the cylinder head raises a question: Why is there a larger housing above the exhaust cam's sprocket (yes, the cams are chain-driven) than above the intake cam? Could that bulge conceal a powerband-broadening exhaust cam phaser? Such variable valve timing could give this engine Harley-Davidson-like bottom-end torque, just as it does in my wife's Chevy Trailblazer. The location of the cam-chain tensioner on the rear of the right-side-mounted chain housing indicates forward engine rotation.

Yamaha

Four large tapped engine-mount bosses, two in front of the head and two behind it, suggest that the engine is vibrationally smooth. Positions for two more long through bolts at the rear of the gearbox further confirm rigid mounting.

Projecting forward on the left side of the front of the crankcase is a round oil-to-water heat exchanger with a spin-on oil filter. Two exhaust header pipes snake to the right to clear the filter then swoop left again before turning under the front of the case to join in the beginnings of a muffler (cut off for display). There is a threaded position for an oxygen sensor in the front of this muffler, indicating the intention to make this engine widely emissions compliant.

Two sparkplugs are centrally mounted, suggesting that this is a four-valve engine. An integrated stick coil/plug cap, indicated by its low-voltage connector, fires each plug. The water pump is located beneath the large clutch housing on the right, and there is a thermostat housing on the left side of the head.

We can imagine this muscular, high-torque engine powering a variety of relatively simple and therefore appealing new motorcycles. Successful bikes always have a narrative—a story. There was no narrative for the TDM, so dealers and prospective buyers didn’t know what they were, and sales were disappointing.

Let’s hope for better.

View images in photo gallery:

New parallel-Twin is compact, may displace as much as 903cc.

Yamaha?s FZ-09 Triple is on left, new Twin on right.

What?s that suspicious bulge in the Twin?s exhaust-cam housing?

Header pipes shimmy past oil cooler/filter combination.

Dancing metal: swoopy exhaust counterpoint.

This new engine is very short from front to back.

Oil-level sight glass and sump below.

Centrally located stick coils, breather in cam cover.

Hefty engine mounts, nice castings, simplicity.

Thermostat housing, tight water-jacketing.

Big throttle bodies, with the cam-chain tensioner to the right (What?s that low-slung maxi-scooter in the background?).