When the S chassis was a popular platform for sno-crossing there were a lot of Bombardier sponsered mods available to strengthen the somewhat flexi S tunnel. Some of the flex was reduced in the newer ZX chassis by making the steel inside skid mounting brackets one piece front to back. For the MXz, Formula Z and other S based frames the steel tunnel reinforcements were separate for the front and rear. The end results were inside ski lift. Accellerating hard out of a corner with your front shocks set at a stiff spring rate would lift the ski due to tunnel twist all the way down to having the running boards bow or the tunnel kink after some intense jumps. The kinks would start to appear right under the seat bolsters on the sides of the tunnel if you landed her on the rear grab handle. The first telltale sign was the seat began to have a wider gap between the lower edge and the tunnel and the gap up front at the fuel tank would widen. Bombardier's racing department of that time was well aware of this issue and released a tunnel reinforcement kit as an accessory for the '99 MXz & MXz TH edition. The kit essentially is a junction plate which ties the two skid mounting plates together on the underside of the tunnel. Unfortunately for some of us S owners said kit has been discontinued for some time. Recently I spoke with a few old school sno-pro racers and mechanics and found the part numbers for the plates individually.

518 321 426 Plate-Junct. LH
518 321 427 Plate-Junct. RH

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The kits ties the mid to the rear tunnel plates where the trouble begins.

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The rear mounting bracket suffers a lot of fore - aft flexing on washboard trails and becomes more apparent when newer coupled skids are upfitted. The problem being that the base SC 10 skid elevated the tunnel & therefore the CG (center of gravity) high making the rear end tippy and prone to twisting at the limit. Some evidence of this is the fact that the juctions fit perfectly on a new (unbeaten) sled and rarily line up on an experienced chassis. FAST M-10 knew this and released a long tunnel stiiffener / mounting plate. The AD Boivin also recognized the the problem which made their ARM suspension better that the Bombardier licenced unit.



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Note the missalignment when the factory rivet is centered in the juction plate. The righthand side of the bridge should ride against the raised bead of the rear tunnel bracket.



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No big deal, you can elongate the large rivet relief hole and line up the junction perfectly.



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On the outside I used some BRP yellow powder coated rivets to make a clean installation. One problem with the yellow rivets is that they only come in a somewhat long 3/4" reach. This makes quite a protrusion inside the tunnel to catch ice build up. Paul Y did a post on using shorter rivets when installing tunnel reinforcements (fish Bones) on sleds which was right on the money. "After riding in slush or wet snow the track would contact the sides of the tunnels build up and vibrate".


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Here's what I doo to shorten the rivets and lessen the protrusion inside the tunnel. Just pop the stud out of the rivet and cut the shank down to the size you require keeping in mind that you will need a minimum of 3/16" to hold the ball inside.

Here's another measure I took to keep snow build up on the inside and black scuff marks on the out side of the tunnel. The product is clear urethane tape which is soft and 6 mils thick. I also applied it under the seat and on all the leading edges of the underside of the sled. On installation the same rules apply as installing decals. This stuff is used to prevent stone chips on automobile hood and rocker panels. I insulated the fuel tank / tunnels contact points with high density foam tape to eliminate the gray stuff that bleeds out from under the seat & tank on S sleds.





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It will be interesting to see how the urathane tape holds up. May be a good way to keep the polished look
As always lots of great tid bits Simon

Thanks

Good point James,

I did apply some to the polished bracketry to see if it keeps the shine. The stuff is quite expensive $20.00 per sq ft. I might doo the Adrenaline with it later.