Ski-Doo models fitted with the 1000 SDI engine are fitted with an all new drive system, developed specifically for the incredible power levels produced by the monster twin (170+ HP). The most obvious change is the relocation of the brake disc to the outside of the chaincase. This allows the chaincase to be mounted directly against the tunnel, which shortens the driveshaft by almost 2â€, reducing rotating weight.
Another benefit to mounting the chaincase directly against the tunnel is the case becomes considerably more rigid with less flexing under load. Also, the hub area of the case and bearings benefit from greater contact with snow in this position, so they can operate much cooler.
While this new design chaincase is plenty long to allow the use of the larger diameter 10-tooth track drivers, there are actually two different lengths of RT chaincases; The Mach Z center-to-center is 202.5mm, while the Summit RT models are 233.5 center-to-center. The longer case on the Summits provides additional clearance (now at a full 3â€) for the taller 2 5/16â€ lug tracks as well as to provide a shallower approach angle (23.6Âº) for deep snow flotation.
By moving the brake disc to the outside of the chaincase, the jackshaft now passes through the chaincase cover via a pass-through bearing. This extra bearing adds a great amount of support to the jackshaft and helps to keep the chain and sprockets in near-perfect alignment. The disc itself is over two pounds lighter due to its wave shape and a much smaller splined hub. By using a splined hub the disc is very solidly attached, which gives a more positive feel and does away with keyway noise and rocking. The disc also runs much cooler due to its mounting outside the case, with cold air being directed at it via hood louvers.
The new chaincase was designed to allow larger top and bottom sprockets to be used, which was needed to compensate for the larger diameter track drivers. Mach Z models are fitted with a more efficient â€œrockerâ€ style chain (1.5% more efficient to be exact) and no adjuster as this chain does not stretch (the case is threaded for an adjuster should a gear ratio change be needed, as a standard chain and bottom sprocket could be installed if a smaller top sprocket is required). Summit models use a standard chain and gears, with an adjuster due to the smaller top sprockets found in these machines with their longer tracks and higher altitude operation.
While both the Mach Z and Summit RT models use larger 10-tooth track drivers, the Summits feature internal/external drivers which reduce track ratcheting in deeper snow and allow for operation with reduced track tension. Mach Zs have standard internal design 10-tooth drivers and an 18.1Âº track approach angle for optimized top speed and handling.