Five historic Rotax snowmobile engines
Snow Goer Tech Professor, Phil Mickelson, has a true bachelor’s pad in Duluth, Minnesota. Aside from various self-made, high-tech gadgets throughout his home, he also has a large mural in his entryway featuring Can-Am motorcycles in action in the 1970s. But most impressive is his Wall of Engines, a dividing wall/trophy case between his kitchen and dining room displaying some of his favorite, collectible powerplants. Try getting that one past your spouse!
Start asking questions, and you realize that each engine in that wall has its own special place in history, and in Phil’s heart. We asked him to share some of those stories, and he developed an 11,000-word document. We then asked him to narrow the list to the top five in his collection.
When I graduated from college, I had no idea I would become involved in the snowmobile industry. I raced motorcycles while I was in high school and college and had quite good success in my region. The year I graduated from college I got a call from Halvorson Equipment Company in Duluth, Minnesota, a distributor of Ski-Doo snowmobiles. They were expanding their racing team and wanted me to help build racing engines for their team.
I was dropped into a team that included Steve Ave, George, Stan and Doug Hayes, Jake Kimbal, Ed Schubitzke and Jim Bower. While I didn’t know much about snowmobiles when I joined them, I learned about them in a hurry from that team.
Steve Ave was the reigning Eagle River World champion in 1968 and I had a chance to work with some of the most incredible engines of the day. I knew that many of the engines I worked with would become points of reference in the future and I had the opportunity to collect some of them.
This article defines five of my favorite Rotax snowmobile engines in my collection, starting with number five and working down to my number one favorite in the collection.
5. Serial No. 103, Rotary Valve Single Cylinder,
334.5cc, Bore 78mm, Stroke 70mm, 39 hp @ 7000 rpm
This is certainly one of the most interesting and rare engines in the collection. It is a prototype single cylinder rotary valve engine that Rotax created in 1969. It could have become the 1971 340 Blizzard engine but Polaris’ new clutch sent Bombardier and Rotax back to the drawing boards for future racing engine/clutch designs.
With the clutches used prior to development of Polaris’ design, low-end power was a must, and the broader the power band was, the better the design could perform. The rotary valve design allows a much longer intake duration while still being able to close the intake port before losing any fresh charge back out the intake port. It also frees the rear of the cylinder for additional transfer ports. The design effectively widens the power band while being able to make more peak power.
This particular engine has no magneto or external flywheel. It is equipped with breaker points, which ride on a cam ground directly onto the crankshaft. The points mount on a rotating plate which can be positioned by pushing or pulling on the rod that comes out of the “magneto housing” beneath the coil. The engine could be retarded manually for starting. The system used a battery to power the coil and was termed a constant loss ignition system.
Helmut Roteh, who was in charge of Rotax R&D, brought this engine with him on a visit to Halvorson Equipment Company. Through a translator, Roteh explained the engine’s design and features and left the engine for the Halvorson R&D department to test. The RV engine made its way up to Doug’s Inc. in Virginia, Minnesota, for Doug Denhert to make a pipe for it. The engine was not legal for use in anything but the open class where it was just too small to compete. Doug did race the engine once (illegally) just to see how it would compete. It was impressive but Doug backed off so he wouldn’t make the final and a possible inspection.
4. No Serial Number Tag, 339.2cc, Bore 2 x 59.5mm, Stroke 61mm, Type 354 engine, 103 hp @ 10,800-11,200 rpm (modified)
This engine represents the highest level of development of the central rotary valve, liquid cooled Bombardier-Rotax engine. This engine would have been built in 1984. This engine, or a prototype like it, powered Michel Gingras’ twin-track racer that won the 1985 Eagle River World Championship.
The engine was a prototype for the Rotax Adjustable Variable Exhaust, or RAVE valve. While Rotax had been working on the RAVE valve system with Can-Am motorcycle engines, 1985 was the first time people had seen such a variable exhaust port on a snowmobile engine. Winning at Eagle River the first time out of the box while all other competitors were racing non-RAVE Rotax 354s certainly proved its value.
Johann Holzleitner, head of Rotax’s high performance department, personally attended to the engine at Eagle River. While setting up for the race, he was not certain both valves were opening at the same time. He added the piece of channel that connected the valves mechanically to ensure that they did open together.
The exhaust ports are the triple design that were added to racing engine concepts by Holzleitner in 1973. Holzleitner’s design has a large center exhaust port with two auxiliary exhaust ports above the transfer ports on each side of the large exhaust port. The design allows a very rapid blow down of the combustion chamber before the transfer ports open.
The spark plugs of this engine are not in the center of the cylinder bore. They have been moved 11.5mm toward the rear of the cylinder. This places the majority of the squish band toward the front of the cylinder, enabling it to remove heat from the hottest portion of the combustion chamber more quickly.
The combustion chambers in this engine are removable separately from the cylinder head, which is effectively the water jacket. Chambers could be interchanged quickly to change compression ratios easily and inexpensively. The cylinder head can accommodate a thermostat.
While testing the engine, it was noticed that the magneto side crankcase was running hotter than the PTO side crankcase. It was determined that the mass of the magneto and flywheel along with no ventilation to the magneto side were allowing heat to build on that end of the crankcase. This is why you see the openings around the magneto housing and recoil starter. A breakerless ignition system is unaffected by moisture flying around so the openings were made to allow air flow to the magneto end of the crankcase.
The type 354 racing engine is one of the highest specific output engines ever built. This little 339.2 cc engine, running on 100 octane gasoline and naturally aspirated, produced 295 hp per liter of displacement!
3. Serial No. 1468064, 599cc, Bore 2 x 76mm, Stroke 66mm, 35 hp @ 6000 rpm (Stock), modified with tuned expansion chambers, ported cylinders, dual HD carburetors, 45 hp @ 6800 rpm (modified). Only used in the 1968 T’NT.
The “600” was the first engine designed expressly for use in Bombardier’s Ski-Doo, not just another industrial engine applied to the Ski-Doo. The snowmobile industry was growing by leaps and bounds and racing was taking off. Helmut Roteh, who was in charge of Rotax R & D, designed the 600.
The engine was a completely new design and became a prototype for the entire snowmobile industry. The engine is an axial fan-cooled design with the fan mounted at cylinder level and driven by a V-belt from the flywheel. The engine also has the cylinders “twisted” to each side to allow the transfer passages to overlap between the cylinders. This allowed the engine to be shorter on the axis of the crankshaft. The design places the intake ports of the cylinder closer together and the exhaust ports farther apart.
The engine was originally fitted with an intake manifold that mounted one Tillotson HR and one Tillotson HD carburetor. A progressive linkage controlled the opening of the two carbs. A common plenum in the intake manifold connects the two intake ports from the cylinders. Since the engine fires each 180 degrees of rotation, only one cylinder at a time breathes from the plenum.
Steve Ave’s 1968 Eagle River World Championship 600 engine was equipped with tuned expansion chambers, dual Tillotson HD carburetors, ported cylinders and openings in the sides of the pistons to allow fuel mixture from under the piston to escape directly into the transfer ports.
The 600 engine in my collection was Steve Ave’s back-up engine. The engine was installed in a beefed up Super 370 chassis and became the first T’NT model in Ski-Doo’s line of snowmobiles. Only 117 model year 1968 T’NT 600s were built and it is one of the most collectible Ski-Doo models ever built.
2. Serial No. 1398732, 494cc, Bore 2 x 69mm, Stroke 66mm, 16 hp @ 4000 rpm (stock); modified with ported AS 250 cylinders, Tillotson HR carburetors and tuned expansion chambers, about 35 hp @ 6000 rpm.
Bombardier never used this 494 in a production Ski-Doo. Like all Rotax engines used in that day in a Ski-Doo, it was another industrial engine produced by Rotax but was underpowered, heavy and not well suited to application on a snowmobile. The vertical twin had cast iron cylinders and heads with a single Bing carburetor facing forward, as it would have been applied to a Ski-Doo. A large radial fan housing on the right side of the engine made it difficult to mount on top of the chassis tunnel.
Wajax, a company in Montreal, Quebec, imported Rotax engines for industrial applications. Roger Langlois, a very successful Ski-Doo racer from Montmagny, Quebec, contacted Wajax in 1966, explaining that he was in need of an engine capable of powering a peat moss harvesting machine he was working on. Langlois was able to acquire five 494 engines from Wajax. He knew the engines weren’t going to compete in the unlimited class in their stock configuration but it was a Rotax engine and would be legal for use in a Ski-Doo for racing purposes. Langlois brought the engines to a friend, Jean-Paul Samson, who was involved in two-stroke engine modification.
Samson modified the cast iron cylinders and installed straight pipes and dual Tillotson carburetors. Langlois showed up at a race in Quebec City with the first 494, devastated the competition and word about the 494 was out. Samson was the first engine modifier I know of to convert a fan cooled engine to a “free air” design. The cooling fan takes power to drive it and Samson wanted to do away with it and let the passing air cool the engine for “free.”
Some 494 engines ended up making it to Idaho Falls, Idaho, where Gary Scott, Doug Denhert and Mike Cutler started doing some real magic with them. Scott had designed and built the first tuned expansion chamber for use on a snowmobile for the aluminum cylinder AS 250 Rotax engine which was first used on the 1966 Super Olympique. He had a lot of experience modifying the AS 250 and the bore and stroke was the same as the 494.
The Idaho Falls group contemplated the use of the AS 250 top end on the 494 bottom end. The problem was the cylinders wouldn’t fit on the crankcase as a twin. Denhert was the guy who said, “Let’s just saw through the cylinders and heads, right through the transfer ports, then weld a plate over the transfers where we cut them open. We should be able to come up with the clearance we need between the cylinders and still have a decent transfer port cross section at the center of the engine.” It worked!
The 494 had an enormous kick off from the inspiration of Langlois and Samson but the efforts of the Idaho Falls gang of Scott, Denhert and Cutler turned the 494 into a nearly unbeatable race engine. While winning championships all over North America during the 1966-67 winter, the 494 picked up the Eagle River World Championship driven by Duane Frandsen.
1. Serial No. 244/732, Rotax, LC Can-Am engine, Prototype engine, 51mm bore, 61mm stroke, 124.5cc, about 32 hp @ 9000 rpm on methanol
At the time of this writing, this engine still holds the modified, 125cc, semi-streamlined class, (APS-AF-125) Bonneville Salt Flats world speed record of 136.537 in 1973. For comparison, a Bonneville-prepared Yamaha, factory prepared, ran 112 to 115 at the same test event that year. The Can-Am record was set in 1973.
The bike was designed and driven by Robert Barker, an engineer with the Can-Am Division of Bombardier, Inc. Barker was a well-known road racer of his time and worked on the design of many of Can-Am’s future chassis designs. Tuning Barker’s bike and assisting at Bonneville were Gary Scott and Mike Cutler. They were well known motorcycle and snowmobile racers and they really knew two-stroke engines.
The engine was the first to come from Rotax with triple exhaust ports and NiCaSil plated bores. The cylinders were in the midst of design for Ski-Doo’s new series of racing engines. This cylinder was first used in a Ski-Doo on the factory race team IFS sleds in model year 1977. The cylinder design also showed up on the 1977 Blizzard X modified sleds, with leaf spring front suspensions, which were used by independent modified class racers.
Gary Robison, the man in charge of Can-Am design, was well connected with Rotax and must have seen the application of the new Ski-Doo racing cylinder on its motorcycle. I believe Rotax modified the molds of the Can-Am crankcases to allow the transfer flow and coolant flow that was required to allow the use of the new snowmobile cylinder design on a Can-Am engine.
A coolant outlet was welded below the front engine mount and a type 254 Ski-Doo cylinder head was cut off near the coolant passage and a plate was welded over it to seal the cooling jacket.
The longest stroke engine built in 1973 for Can-Am was 57.5mm. This engine has a 61mm stroke, which matched up with the Ski-Doo racing engines that this top end was borrowed from. This historic engine has a one-off crankshaft in it.
The engine had no water pump and was thermo-siphon cooled. The backbone of the frame, which was normally the oil tank for Can-Ams, was used as a coolant reservoir. There was no oil injection pump on the engine and the oil was premixed with the fuel.
This engine is certainly one-of-a-kind and has held a Bonneville speed record for 35 years. It is a wonderful example of combined snowmobile and motorcycle technology of its time.