By Hal Armstrong
Back in 1979 when Polaris Industries was celebrating 25 years in business they were a much different company, producing only snowmobiles. That wasn’t the only difference: their engine supplier was Fuji Heavy Industries (a.k.a. Subaru) who had been working with them since the late 60’s. Polaris had worked with Fuji to build a number of three cylinder engines since 1970 for their race sleds. The first production triple was introduced in 1972 as the TX 500 Limited. I remember when these came out and it was an over the top production sled featuring a 500 cc three cylinder free-air engine with three Mikuni carbs and a three into one exhaust. The sound it made was magic!
The TX 500 was in production until 1975 when Polaris introduced the redesigned 1976 TX free-air models (250, 340, 440) based on the successful Starfire race sled chassis. It would be three years (1979) before the first triple liquid appeared. The new 500 Fuji (Superstar) motor was the forerunner of the 600 and 650 Indy triples that propelled Polaris to become the market leader during the late 80’s and 90’s.
Polaris marketing recognized the void in their lineup when Arctic Cat, Yamaha, John Deere and Kawasaki had 440 cc liquid cooled performance sleds in their lineup. While Polaris had released the highly successful TX-L in 1977 to compete in the cross-country wars, and it was wicked-fast for a 340 cc production sled, the new 440 cc LQ sleds, however, were selling like hot cakes and Polaris knew they had to up the ante. With the company’s 25th anniversary on the horizon the engine department (led by Jerry Schenk) began work on the 500 triple liquid.
The First Production Liquid Cooled Triple
Polaris had been cleaning house on the oval tracks in 1977 and 1978 with an all-new 440 cc triple liquid-cooled Fuji motor housed in the all-new RX-L chassis. They were running two different versions of the 440: one had 6 ports, the other had 8. Everyone wanted a production version of the 440 triple and Polaris finally offered it – bumped up to 500 cc.
Polaris labeled their motors “Superstar” and for good reason. They built the new engine using the short (55.6mm) stroke that Polaris had been using since ‘76 on the 250 cc and 340 cc engines. The 500 was essentially a 2+1 version of the 333 cc TX-L engine. The triple used 6 port individual cylinders and heads on this first version of the famous Polaris triple. The mono block triples would not appear until 1993 with the 580 cc XLT.
Fuel delivery into the intake ports was with Mikuni VM34 round slide carbs sucking air through an intake box, which drew air from behind the windshield. Typical of all early Polaris motors was the piston port induction (intake) with the exhaust ports connected to a three into one manifold that had been used on early Polaris Free Air triples dumping into a tuned pipe and silencer. The result was the best sounding sled to hit the snow, and even today the sound of a triple two stroke is music to any motorhead’s ears.
Polaris tuned the motor to run between 7800-8000 rpm’s claiming the power was close to 100 hp which, back in the late 70’s, was equivalent to owning an 800 cc sled of today. There were no fuel mapping and temperature sensors monitoring air temp, engine temp, and throttle position. Fine-tuning the motor was a matter of knowing how to jet your carbs for air temperature and barometric pressure. Times sure have changed. Plug fouling was always an issue with the triples if the carbs were not set up just right, also due in part to the much weaker spark ignition systems.
The 500 triple used a thermostat located on the coolant outlet with the coolant entering through a water manifold above the exhaust ports flowing up through the head and exiting out the rear of each cylinder head into a common header. The water pump was belt driven from the crank on the recoil side, as was common on these early liquid cooled engines. Polaris was unique in that they mounted the heat exchangers beneath the running boards. While some manufacturers were using under hood radiators or tunnel mounted heat exchangers, Polaris’s heat exchanger location first appeared on the ‘77 TX-L and was proven to reduce ice build-up in the tunnel as well as strengthening the running boards for pounding the moguls. The Centurion triple was also the first Polaris model to use a cooling extrusion mounted in the front bulkhead which is now standard on all liquid cooled sleds built today.
Rubber Tracks and the Dawn of Long Travel Rear Suspension
Polaris had never been partial to rubber tracks, but in 1979 they moved to the 121” rubber track from the 114” cleated track that had graced their performance sleds for years. The rubber track to have back in the day was built by Yokahoma and came pre-studded from Polaris with – get this – just 24 studs! Power was delivered to the involute drive from Polaris clutching which, even in 1979, was still the class of the field with incredible efficiency, making the Polaris sleds super-fast for their respective power levels. The track, however, was overshadowed by the new rear suspension. In fact, while the 500 cc triple caught everyone’s attention at the dealer, the all-new long travel suspension would morph into many iterations over the years and this basic layout is still used today on the 2016 Indy!
The increase in travel from 2.5” on the ‘78 TX-L to 6” on the Centurion was mind boggling in the day. A 5-position spring preload coil over shock controlled the front torque arm with a front limiter strap to adjust ski pressure. The rear scissor arm was all new, using torsion springs and a center mounted shock much like today’s coupled suspensions. Polaris engineers back then realized that separating the damping from the spring rate would improve the ride over small and large bumps. Aluminum rails and multiple idler wheels to reduce hyfax wear rounded out a new skid frame that was a quantum leap over what it replaced.
New Styling and Leaf Springs
The Centurion hit the snow with new body styling that put the headlight up near the windshield and a new enclosed hood to reduce noise. The graphics package was right off the ‘78 RX-L SnoPro race sled and even today ranks as one of the best looking Polaris sleds ever made. The refined styling extended back to the new seat design and center mounted fuel tank. Hydraulic brakes were still a Polaris exclusive on a production snowmobile. Total weight? 425 lbs with a 7-gallon fuel tank. Oil injection? Not yet. Polaris still had you premixing your fuel in 1979.
The only disappointment with the first Centurion was the continued use of the mono leaf spring ski suspension. Meanwhile, their IFS race sleds were dominating the racetrack. While leaf springs were still the norm for a production snowmobile in 1979, the consumer knew that IFS for the trail was right around the corner. Owners of the Centurion or the TX-L would see the first Indy’s hit the cross-country circuit in the winter of 1979. Two years later in 1981 the first Indy Centurion with the 500cc triple would hit the snow.
The End of an Era: The Beginning of a New Chapter
The leaf spring Centurion would return for the 1980 model year to close the era when high performance snowmobiles would be built with a leaf spring ski suspension. The new long travel rear suspension and high power liquid triple engine simply outperformed the last hold over from the 70’s. The 80’s would usher in the era of long travel front and rear suspension designs. The late 70’s in the snowmobile industry had seen resurgence in sales and when Polaris entered its 25th year in business the Centurion was a landmark snowmobile for the company. It truly showcased the best the company had to offer. Polaris advertising in 1978 proudly proclaimed “One Going Machine is Coming” in anticipation of the Centurion – named, of course, in reference to having 100 HP, but also in its ability to reach the coveted 100 mph mark.
While the Centurion was an expensive ($3600.00) snowmobile for its time, the demand for these sleds outpaced production. These sleds, in fact may have saved companies like Polaris in the early 80’s when the economy went into a recession combined with high interest rates (20%) and two low snow years. It was the perfect storm for the snowmobile industry. Sled sales plummeted and Polaris almost closed its doors. Looking back, sales of the higher price and more profitable Centurion and TX-L models earned enough cash to keep the company in business.
The Centurion was the first true muscle sled that ushered in the sled wars of the 80’s and 90’s. The triple cylinder Polaris motors were the foundation for the explosion of the after-market performance shops that produced everything from tuned pipe sets, clutching and carburetion mods for the Polaris triples. Speeds of 100 mph would now become the norm and consumers who wanted more power were lining up at the doors of these shops.
The 500 cc triple was in production until 1982. Polaris, answering the call for more power would increase the bore to make a 600 in 1983 and finally the 650 in 1988. Polaris continued with the basic motor design until 1998 when the move to reduce weight with the big bore 600 and 700cc twins would evolve into their USA-built Liberty engines. Twenty years with the same basic engine reveals just how popular the Polaris triple was. Even today rumors continue about the return of a new Liberty triple with semi-direct injection. Would you buy one?