Yamaha RX-1

Finally... a high tech four stroke sled with performance
RELATED TOPICS: ENGINES | YAMAHA | SNOWMOBILES
When Yamaha announced the RX-1last winter, snowmobilers couldn't stop talking about it. The Yamaha crowd talked about how proud they were that their brand of choice had flexed its motor muscle.

Biker heritage
Yamaha built its Genesis Extreme sled engine on the R1 motorcycle program. You'll find the inner workings to be directly peeled off the bike, while the external castings are designed to fit it into the sled chassis. The camshafts and cam timing come from the '01 cycle as do the intake valves.

The exhaust valves are derived from the '02 bike, but use a higher nickel content material to cut 2 grams each. The timing scheme goes like this: triple 23mm intake opens at 31° BTDC, closes at 57° ABDC; dual 24.5mm exhaust opens at 60° BBDC, closes at 36° ATDC.

The cylinders are very over square, short strokers, measuring 74mm across with a 54mm stroke. The pistons come right off of the '02 bike engine. The combustion chamber is also straight from the R1, with a compression of 11.8:1.

The dry sump oil system uses the same spin-off filter can as the R1 and FZ1, so they will be readily available when the time comes.

Yamaha is touting the RX-1 engine as incredibly durable. It is recommended to change the oil after the initial break in period is wrapped up, about 500 miles. After that, do a change once a season or 2,000 miles. At about 25,000 miles of service, Yamaha recommends a valve train inspection. That's rugged!

The crankshaft is a new piece, made specifically for the RX-1. The PTO shaft is connected to the primary clutch via a rubber-isolated gear reduction system. This reduces the engine RPM by a 37:31 ratio to help keep the clutches safe.

On the Dyno
Yamaha also built an engine protection system into the design. If the coolant temperature is below -4°F, it bumps up the idle, but limits engine RPM to get everything warmed up before you pull away.

On the flip side, if you heat up the coolant to over 212°F, the ignition shuts down to idle for three minutes or longer until it is safe to ride again.

We put two different sleds on two different dynos to make sure we were accurate with this test. Our second sled had been slightly broken in and showed a little better. We pulled a peak torque of 92 pounds at the clutch shaft at 6112 rpm. The top horsepower came in at 137.2 at 8714 clutch rpm, which translates to 10,400 rpm on the engine tach.

Our first test sled was absolutely brand new, with only as much running time at it took to warm it up. Dynoport's dyno reported 135.3 peak hp at 8600 clutch rpm, which shows that break in starts early and is absolutely necessary to get the potential from the engine.

While the peak horsepower was down from what we expected, the torque and horsepower in the low and midrange is phenomenal. "Our dyno absorption unit could not hold the engine below 5000 engine rpm," said Dynotech's Jim Czekala. "Two stroke sleds are off the pipe at those low speeds and can easily be controlled on our dyno at 3-4000 rpm. Not so with the RX-1."

A development engineer at Yamaha told us we should expect more power from the engine as it matures. "I usually see about eight horsepower gained from a brand new motor, once it has been fully broken in," he said. "These engines take a long time to break in. We run ours under a very tough program. It'll take consumers a while to soften them up to reach their full potential."

The good news in all of this is that the RX-1 starts out with a ton of clutch torque and holds it above 85 lbs. from 6500 to 9600. Plus, it just gets better with age. Bikers say the R1 comes on at 1,000 miles. Sleds should, too!
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