March 2015 Ask the Experts

Check those cranks, rattles and let's roll!
Chassis Switcheroo
Q What is needed to swap an F chassis 600 triple to a CK3 chassis? – outlaw fab shop

A The cases are different lengths, and a CK3 600 has a longer crankshaft stub. You will need to modify motor mount holes in order to properly align the clutches. – catracer03

Big bore pipes

Q I’m putting a 770 twin into a 2003 440 REV chassis. The motor is a Chuck Walters 770, a 700 twin bored out and sleeved for the 800 twin piston using the 600 H.O. Y-pipe, but what pipe should I use? Would an 800 REV with a stinger reducer work? – ski-doo ps 1000

When choosing a pipe for big bore applications, the stroke is more important than the actual cc of the engine. The 770 engine into the REV chassis would best warrant the 600 H.O. designed single pipes. This would be a great start for your application. The stinger diameter may or may not need to be larger, as this depends on more than just cc of the engine. Straightline has tested and sold its 600 H.O. pipe to the 600 and 700 big bore applications with great results. – Jason Houle, Straightline Performance

Clutch swap
Q Will the primary and secondary clutch from a ’98 SRX 700 work on a 2000 SRX 700? – tslutter

A The fitment should be the same and the calibrations will be similar. I believe the 2000 may have had a couple more horsepower, so you may need to adjust fly weight values a little. – dyna-tek racing

NOS reeds

Q What is the best reed to use for nitrous? This is a wet kit injected into the carburetor after the slide. – sledhead-2

A The best reed we have seen is a high-end carbon reed, depending on the amount of nitrous. Most stock reed applications can handle a trail size 30 hp with no concerns. – Jason Houle, Straightline Performance
Bogging Blues
Q I have a Polaris Indy 500 I bought for this winter, and it will run great for about 15 minutes and then just bogs badly. Any ideas? – Collin1020

A Sounds like you have too much fuel getting to the engine. You may want to double check the choke. Make sure it isn’t sticking and dumping too much fuel to motor. – bman

Stutter box help
Q I need help wiring up a stutter box. The box has four wires: black, red, white and blue. White and blue were wired to the button, and black to the ground. Red just had a long wire with a connector on it. I have no clue where to wire it to. I should mention this is on a 3-cylinder Rotax engine with a VDO tach. I’m not sure on the make of the stutter box. It has no markings on it. – RJD

A Red is your hot power and goes to the button powering the stutter when pushed/powering the box. Black is your ground wire. White connects to white on the trigger. Blue connects to the kill wire on your CDI. – oldschool780

Check the chain

Q My 1998 ZR600 stopped moving. The sled was driving fine with no noises, then just revved up and won’t move under power. The brake disc spins, but the track won’t engage. The track is not bound up. I can roll the sled with no binding. Where do I start to find the problem? – nos nut

A You need to take chain case cover off and start looking for broken parts. You may have to remove the muffler to get at it, and possibly the battery too if it has one. I think its 6 bolts (13mm). Make sure you find all bolts, and then the chain case cover should come off easily. – teamarctic64

Brake relocation
Q I am considering relocating the brake on my ’97 Ultra asphalt drag sled from the jackshaft to the drive shaft. I have talked to a few people regarding this. Some systems require machining the drive shaft round where the hub sits and machining a keyway. Other designs have the brake hub just sliding over the shaft without machining it round and allowing the hub/disc to float on the shaft. I have a 1-1/8-inch titanium drive shaft and could obviously use either set up. I was a little concerned with using an aluminum hub that floated because of wear issues. I was also told that some of the setups with a keyway and key can wear and fail as well. Any advice would be appreciated. – uncle vinny

A An easy setup is bolting the disc solid on the drive shaft with a hex hub and using a dual opposed piston brake caliper so the pads can self-adjust to the disc location. – dyna-tek racing

Mig or tig
Q I’m in the process of building a high HP 2-stroke and feel it’s time that I weld up the crank gears on my Yamaha V-max 4. I’m looking for advice on how others are doing it. Mig or Tig? Wire or rod type? – jabber

A Tig. Make sure you ground the crank web and not the bearings. Electrical arching through the cages and balls will “spot” the bearings. – Clayton

Bearings bear mentioning
Q I am replacing the bearings on the cog shaft of my 2001 Arctic Cat Pantera. The clutch side broke. When I try to tighten up the gear side it pulls the shaft out of the clutch side. Even with the set screw as tight as I can get it just pulls the shaft off the bearing any ideas? – schaff

A The bearing on the clutch side should be flush with the very end of the shaft, and the bearing on the chaincase side needs to be installed with the shoulder for the lock collar toward the bottom gear. Obviously there is no locking collar on the chaincase bearing, but it does use the shoulder as a spacer. If it is not installed correctly it will pull the drive shaft toward the chaincase side of the snowmobile. Make sure all of the bottom gear parts are in order or it will have the same effect. You can use online microfiche to determine parts orientation. – dyna-tek racing

Need an extension?

Q I am replacing my 121-in. suspension with a 136. I have the material bought to make my own tunnel extension, but I am wondering what the exact measurement is that I will need for the extension? The measurement I need is how long the extension actually needs to be (6, 7, 8 inches?). I don’t have the suspension or track yet, so I can’t put it in place and size it up. – polaris680

A Tunnel extensions are more precise than just adding material. The manufacturers spend large amounts of time on determining this distance as it is crucial to snow flap location, and chassis strength. The snow flap location controls the sled temperature and aids in slide lubrication. The best suggestion is to measure and duplicate the manufacture that you are extending and match that 136-inch tunnel the best to you can. Lastly, be sure to run the 136-inch snow flap too. – Jason Houle, Straightline Performance

Drag clutching
Q What is a better clutch for drag racing, the lightweight Forge TRA3 or the billet that Bellman makes? Does it depend on the type of racing that you are doing? – max rotax

A The Bellman Billet TRA was built for today’s high horsepower drag sleds. It was patterned after the TRA 2. The Billet clutch is a little larger and heavier than stock. The sheave thickness is greater and consistant from top to bottom to take the flex out of the sheaves. We also removed the tapered outer diameter from the moveable half of the clutch, which resulted in slightly larger diameter. The Bellman sheaves are cut on our specified straight angle. The OEM TRA parts are perfect for 95 percent of drag racers tuning with TRA clutches. The Billet parts filled the void for the other 5 percent. – Jamie Bellman

Sprocket size

Q What is the largest size of drive sprocket I can put on a CK3 with a Crank Shop chaincase for asphalt racing? – machz975

A Try sizing with a tape measure. I believe it’s 11-tooth 2.52. – uuubb
Experts challenged
Q Love the magazine, so I will reluctantly point out in your ‘The re-evolution of race sleds’ article (Jan. 2015, p. 42) the first sled to introduce the rebuildable FOX shock was the 1990 Arctic Cat EXT Special (only 300 made). I know this to be true as I was a factory-trained mechanic for 10 years at a Ski-Doo/Arctic Cat dealer in this period. – Dan Woods

A Dan, you are correct and thanks for reading AmSnow! The first sled to have FOX shocks factory installed was the ’90 EXT Special. However, the ZR was the first lineup to popularize the FOX shocks to both racers and consumers as compared to Limited model special builds. Racing really pushed the factories to improve their sleds, and a lot of those improvements made it down to the consumers within a model year or
two. You can still see the same progression on today’s sleds. – Joe Rainville
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