Extended chaincase

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Why should I buy an extended chaincase, when I can just roll the stock one?

A factory Yamaha Chaincase has a 7” center-to-center distance.  The top shaft is 1” in diameter.  Therefore, the distance from the center of the drive shaft to the outside edge of the jackshaft is 6.5”.  The radius of a 7 tooth, 3” pitch driver is 3.4”.  A 2.5” paddle track is 2.75” thick, including the belting.  The total measurement for the driver and track is 6.15”.  That leaves .35” clearance.  No wonder Yamaha uses a 2.25” Maverick track.

Here’s something to consider.  The anti-ratchet points on your drivers are .7” long.  If you have any looseness in your track the track will climb out those anti-ratchet teeth.  After all that is what they are there fore.  The gap between the jackshaft and the tips of the track paddles decreases.  If you run your track loose enough the paddle tips will hit the jackshaft before the anti-ratchet points are disengaged.  Several things could happen at this point. The paddle tips could bend over, the chain might break, or you will spin out the centers of your drivers.  Remember if the last two happen, you will lose your brakes and maybe your sled, depending of the position you are in.  If your sled is set up like this, remember not to run your track too loose.  The above has happened to me twice, before I figured out the problem.  I’m a slow learner.

In short, rolling your chaincase will work, if you use your stock driver size and don’t run your track too loose.

The center-to-center distance on our extended chaincase is 8.3”.  That gives you an additional 1.3” to work with.

One last thing, our case is made big enough so that you can use a 46-tooth gear on the bottom.  You will now have a wider selection of gearing ratios available to you.

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Why should I be aware of my track’s approach angle?

Depending on how long you have been snowmobiling, you have seen track lengths increase from 118” with a .75” lug to today’s 174” with a 2.5” paddle.  The bigger tracks have a larger footprint and move more snow.  This really helps when we are trying to get around in the soft snow. 

Today’s manufacturers have designed super suspensions, with up to 14” of travel.  That is great for bumpy trails, but soft snow sleds don’t need all that suspension.  The snow is already soft.  Most of today’s production sleds have 50-55” of track on the ground.  That is of course if you have a 162” track. There is about 12-15 inches of track that comes off the bottom of the drivers and hits the leading edge of the rails.  We will be talking about this area.  On a stock Yamaha this track angle is 22 degrees.

Try to imagine what is going on under your sled.  The first 12-15” of your track is trying to lift the front of your sled out of the snow.  If you had a zero degree approach angle, you would have up to 70” of track pushing your sled forward at 100% efficiency.  That would make a huge difference.  The problem with that of course, is that you’d have no suspension travel.  A compromise has to be made.

If you install our extended chaincase, you have the option of going to a bigger driver.  You can use an 8-tooth driver or even a nine.  An Apex with our chaincase and 8-tooth drivers has an approach angle of 14 degrees.  Personally I’m going to try a nine-tooth driver.  My approach angle should be around 10 degrees.  I’ve never ridden a sled with such a low angle.  I hope that this angle and a 174” X16” track will make up for the extra weight of my supercharged RX-1.

You will be changing the gearing when you go to a bigger driver.  The wider gearing selections provided by our chaincase will come in handy when you gear things back down.

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Instructions for installing an extended chaincase in an Apex.

We tried to make it easy for you to install this chaincase.  It uses all the stock parts and as many stock mounting holes as we could use.  You will need a 2.5” and a 2.16” hole saw, some pop rivets, and normal tools.

You will have to find someone who can weld aluminum to shorten the right hand cooler and fabricate the flange under the chaincase.  If you want we can shorten the cooler for you.

The first things that you have to do are remove the stock chaincase, left hand bearing, drive shaft, suspension, and right hand cooler.
We need to install the chaincase.  Look at the back of it.  The bottom fits thru the tunnel.  Make cut a circle out of cardboard that is the same diameter as part as shown.  Loosely fit the case using the stock bolts and bolt-holes.  The bottom flange will be in the way.  Cut the flange in two places and straighten it out so that it won’t interfere with the case.
You will now be able to install the case a little tighter, but the bottom won’t go thru the tunnel.  Get inside the tunnel, using the cardboard circle you had made previously, mark the area that has to be cut out.  Cut this area out.  You should end up with something that looks like the picture.

You can now tighten up the chaincase and drill out the new mounting holes.  You can use carriage bolts or relocate the stock rivenuts in these new mounting holes.
The rear of the chaincase should just clear the right-hand foot well.  It will be too close, however, to put the cover on.  You can either cut a hole in the foot-well as shown or hammer a small dent in the foot well to allow for the cover.

You can now fabricate the new flange under the chaincase.  Make it clear the case by about .125”- .25”.  We were going to supply a chaincase cover, but we decided that making a new flange would be easier and stronger.  Plus you can use your stock plastic pieces with a little modification.

The next step is to shorten the right hand cooler by 1.5 inches and relocate the hose bib.  If you get everything in there right, you can reuse the stock rubber hose.

We are now done with the right hand side.

The left hand side will be easier.  We have supplied a template that fits over the jackshaft and in the bottom-bearing hole.  There is an eighth-inch hole in this template.  That is the center of the bearing for the drive shaft.  Drill thru the tunnel using this hole as a guide.  Pop rivet the two round discs supplied to fill the old bearing hole and drill out the new hold using a 2 1/16 hole saw.  Reinstall the bearing holder and you should end up with something that looks like the pictures.  We have provided a ring that will be installed in the bearing holder to make up for the extra thickness.

Lastly reinstall all your parts and you are done.

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If you use an eight-tooth driver you will not have any track tightening issues. The bigger driver makes up for the set back.

There are several gear ratios that you can choose from.  All of these use a 78-pitch chain.  You will have to make one that long out of two chains.  We can supply one to you, if you choose.  The gear selections are as follows:

  1. 21/45 for a 2.14 ratio
  2. 20/45 for a 2.25 ratio
  3. 20/46 for a 2.3 ratio
  4. 19/46 for a 2.42 ratio

If you would like more information on gearing click here.

I would like to thank David Konopatsky of Kono’s 2-cycle and Larry Stinger of Proformance for the help with these installation instructions.

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Here are some pictures of an '03 RX-1 with a 174" track, Avid chaincase, and 9 tooth 3" pitch drivers.
The approach angle is 10 degrees as shown.

Questions? Suggestions?

Email sales@avid-products.com

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