An Icon in the History of Snowmobiling
The spring of 1978 was to mark the beginning of a suspension revolution that would change the snowmobile industry forever. The Polaris Race Team had dominated oval racing for two straight winters with the RX-L oval race sled featuring a twin radius rod/trailing arm independent front suspension (IFS). Polaris was not the first to have an IFS sled on the snow, but it was the first to get the geometry and reliability to the point where the concept worked to its full potential on the ice oval.
With all the success on the oval track and Polaris withdrawing its factory oval race team for the upcoming ’79 race season, members of the factory Cross Country team were anxious to adapt the concept to their 340cc liquid-cooled TX-L, which was the performance trail sled used for cross country. Seeing how the RX-L handled the bumps on the racetrack it was a natural to want to adapt one for terrain racing.
The Cross Country Race Team was made up of veteran Polaris employees who had been with the company for years. Ed Monsrud, Burt Bassett and Bob Przekwas worked in field testing or as development technicians. All three were veteran cross-country racers, with Ed winning the I-500 Winnipeg to St. Paul race in 1975. Let’s just say that these guys were the equivalent of your top Sno-X racers today, except that they worked at the factory Monday through Friday building and testing prototype sleds.
Burt recalls, “We reported to Bob Eastman at the time and had been talking about building a machine to compete in the proto class on the ICCSF race circuit. Bob came to me and said if you want an IFS X-country sled you better build one yourself.” I asked Burt and Ed if they had any direction from upper management, and they told me they did not. The way things worked in those days was that we would build something new, field test and then run it on the racetrack. If it was an improvement it most likely went into production”. Work was started in the spring of 78.
“My goal was to double the suspension travel of the springer sleds. That meant I was after 6” of ski travel. This would also match the travel on our new long travel skid frame that we had developed during the ’78 season. The 1st prototype was built around a ’79 TX-L springer chassis (“springer” was Polaris talk for a leaf spring ski suspension). The front spindle housing cross member was cut off from the bulkhead. I started to weld pieces together and figure out the geometry to minimize bump-steer. Arlynn Saage (from the race department) had done a lot of the development on the RX-L chassis and told me to just build a wood front end for the front of the TX-L to save some time and aggravation.”
You have to remember that back in 1978 we did not have any computer modeling capabilities like they have today. Everything was trial and error. So, I did just that and we started tinkering around with the radius rod lengths and I thought if I went with a taller spindle I could get more ground clearance, which did not work out too well. So that wood mockup was used to finalize the front-end geometry. With the longer travel (compared to the RX-L) the shocks were positioned more vertical. I knew from our work on the TX-L that a 30-degree caster angle gave us more stability when landing from hitting ditch approaches. Originally the TX sleds were built with a 26-degree angle, but we found this to be too aggressive. So the spindle angle was kept the same.”
“The toughest part in developing the front end was minimizing the bump steer and figuring out the steering linkage. I ended up with a steering frog mounted in the center of the bulkhead with equal length tie rods. We did not have the rack-type steering that was found on the CRC front end developed for Indys in later years. The result was .080” of bump steer through out the ski travel – not bad for a first try. So, we built the front shock tower assembly out of 1/8” thick aluminum. We had no idea if this was going to be strong enough, only field-testing would determine if we got it right. The only change we made to fit the drive train from the TX-L was to fabricate a new motor mount plate. The idea was to build the chassis using as many parts from the production parts bin as possible.
Seat of the Pants Test Analysis
The 1st sled was ready in two months and when the first snow fell, testing began. Ed Monsrud tells the story; “We had a test facility out behind the plant where we ran the sled over ploughed fields and logs to simulate chatter bumps, and we jumped it off of docks. We could not believe the difference. We took the sled back to the shop and were just smiling from ear to ear. We told Eastman to take it for a spin. When he came back he said ‘boys, it rides awfully good’. We started building the second sled and continued to field test the original.”
“The first prototypes had a problem with the front end collapsing when we were jumping them, so we had to beef up the bulkhead with additional gussets and bracing. The equal length radius rods also had to be changed. We ended up with the diameter of the bottom rods at 5/8” and 1/2” diameter on top. The radius rods used rod end bearings on both ends to adjust the camber. The trailing arm was chrome molly with a rolled sheet metal covering called an ‘angel wing’ used to increase the surface area of weld at the spindle attachment.”
Bob Przekwas recalls; “You have to remember that all of the parts were sketched out on a piece of paper using as many existing parts as possible. For example, where the trailing arm attached to the chassis we cut off the end of a shock and welded it to the end of the trailing arm. The torsion bar was a piece of square 7075 aluminum. We made a bushing out of solid plastic and cut a square hole in it. Linkage was attached to the trailing arm using linkage made of two rod end bearings attached.”
Shock absorber technology was nowhere near as sophisticated as what we have today for snowmobiles. The team worked with Monroe on the shock valving throughout the winter. Burt remembers, “We used RX-L combos from the oval sled to start with. We were valving shocks on the proto ’till we got them where we wanted them. A pair of shocks would last one race. There was no comparison with the springer sleds as to how fast you could go through the rough, so what you gave up for speed in deep snow you more than gained in the rough.”
Ed Monsrud pointed out, “The big thing was the durability. It was not a huge problem, but the loads were now being transmitted into and through the chassis instead of throwing the sled up in the air. The shocks and springs were now working real hard and the oil temperature would get hot and shock fade was a new problem not really experienced before.”
With all the emphasis initially on the front end, the rear suspension limitations were quickly discovered. Bob recalls, “We were running the proto sled out back on the test track and right away it was evident that the front end would absorb the bumps better than the back end. The back end would not react as well as the front because of the limited travel. We lengthened the front torque arm and the rear scissor arm on the XC-100 suspension that was used on the TX-L. We made several iterations all winter as we continued to develop the sled. The tough part was keeping tension on the track throughout its travel.”
December 10, 1978 is when the competition saw the first Indys. Little did they realize that they were looking at the machine that would bring snowmobile performance and comfort to an unheard of level. Burt Bassett and Ed Monsrud arrived early that morning in a small truck with the two sleds tucked away out of sight. The race was a 200-mile lake race on Lake Vermillion near the small town of Tower, Minnesota. The pair of prototype IFS Polaris race sleds competed in the proto class.
Ed Monsrud remembers what snowmobile journalist C.J. Ramstad said to him when he saw them. “You guys are not really thinking about building these, are you?” Monsrud admitted, “The sleds were not the most finished looking sleds we had ever built. We had used a ’79 Centurion hood and a cobbled together belly pan to keep the snow out of the engine compartment. We finished 1-2 in the proto class. After the race, C.J. came to me and said ‘those sleds are starting to look a lot better now!’ The unusual machines were quickly put back into the race van after the race, but the message had been sent to the competition. Polaris was moving rapidly ahead with IFS development and the bar had been raised.
The pair of proto’s next appeared at the two-day Peace Garden Classic in North Dakota. The race was a 290-mile grinder that ran along ditch lines. One of the Polaris sleds broke down on day 2 with a suspension failure, but Burt Bassett finished the race in the top 10. The center of the bulkhead (where the radius rods attached) had to be reinforced and the ski design would evolve to a bridged design that was used for more than ten years in production untill the advent of the plastic ski design.
The race team ran the sleds the rest of the winter easily. Bob explains; “We ran away from everybody with that sled. It worked great on the lake running because we did not have to slow down for the corners. In the rough, the sled absorbed more than the old springer sleds which would just get launched into the air. We could stay on the throttle while the other guys had to back off or crash!”
Bringing the Indy to Production
The success of the Indy during the winter of ’79 was proof enough for Polaris Management to give the go-ahead for a limited production run. To qualify for stock racing, approximately 1000 TX-L Indys were built. The major change to the design to bring it to production was to shorten the PTO end of the crank 10mm to fit in the new belly pan. All used a 340cc liquid-cooled Fuji-built engine that produced 56 hp and had been in production since 1977. Racers on these sleds dominated the cross-country circuit all winter. No other manufacturer had anything close to compete with it. Yamaha had built a limited production sled with a telescopic front suspension, but Arctic Cat was still working on their design and Ski-Doo was still more than a year away from a production IFS for the trail. Polaris claimed the granddaddy of cross-country that winter winning the 500-mile Winnipeg-St. Paul. In fact, Polaris placed 8 sleds in the top 10. Not bad for the first year in production!
I asked Burt Bassett about how many warranty claims or recalls were made that winter. The only item he recollects was the with the spindle bushings breaking. “We came up with a flat top on the spindle cap and put a washer underneath the spindle so it would not cut the spindle cap and then we were off to the rodeo.”
The trio that developed the Indy never raced the sled in the Winnipeg. Instead, they were busy working on a new design that never made production. “Direct drive was another project the team was working on back then. Cat had been testing an IFS proto sled all winter using direct drive. I ran a 440 liquid with direct drive in an Indy chassis at a few races in 1980. That sled never made it to production. The transmission had merit but it need a larger diameter secondary to get more bottom end and the design was not user friendly for a performance sled”.
Success for Polaris off the Race Track
The Indy came along at just the right time for the company. Polaris got the design right the first year. It was a good thing, because the period between 1979-1982 was a tough time to be in the snowmobile industry. There was over capacity, lots of carry over sleds sitting at the dealers and poor snow in many areas. In fact, Arctic Cat went bankrupt in 1981. Polaris survived those tough years with the Indy leading the way. The competition did not build a high performance liquid cooled sled with IFS. Polaris had this market all to themselves and when the snow came back and the economy got back on track, Polaris would rise from the ashes to become #1 in the market place for many years.
By Hal Armstrong – Follow Hal on Facebook @sledtimemachines