Have you ever wondered why your friend's snowmobile is
faster than yours?
Both snowmobiles are the same make, model, size and both
have approximately the same number of miles. At our research and development
department we have found this very phenomenon to be true. We can uncrate two
brand new snowmobiles of the same model and size and one of them will be a
little faster. Even though they are set up exactly the same, the fact exists
that they are two different snowmobiles made out of different parts with
individual identities and personalities.
Performance is where you find it. To unlock this mystery and
for ease of discussion, lets examine six categories where hidden performance
lies. They include engine, carburetion, clutching, gearing, drive train and
chassis.
Engine
The engine is the primary source of power. If one engine is
more efficient than another engine then it will out perform the other. Several
areas need to be checked. One of the easiest and least expensive is to verify
ignition timing. The most accurate way to check timing will require several
specialized tools including a timing light, battery and dial indicator. Some
manufacturers check ignition timing hot, others with a cold engine. Make sure
that you check the timing according to the shop manuals. Most manufactures will
specify an exact rpm at which the timing is to be checked. If the timing is not
correct, you will need to make changes to improve you performance.
Remove the spark plugs and check them. This is also an
excellent time to check compression. Screw on a compression gauge and turn the
engine over several times. Compare compression reading with the shop manual. If
low compression exists, you will never perform at peak performance until the
problem is repaired. Most low compression problems are the result of scored
cylinders or worn pistons/cylinders from high mileage. Scored cylinders are due
to improper air/fuel mixture or mechanical failure. In any case your local
snowmobile dealer will be able to help you solve and repair the problem.
Another area of lost performance could be a cracked exhaust pipe or leaky ball
joint. Worn exhaust systems may need to be replaced.
The use of RTV high temperature silicone can be used to seal
the leaky joints. New exhaust springs will also help. A leaking exhaust system
will mean lower performance due to a loss of intensity in the pressure waves in
the exhaust pipe, which affects the scavenging of the fuel (the management of
fuel being drawn into the combustion chamber by way of the transfer ports).
Carburetion
A correct carburetion calibration is essential for
snowmobile engines to run correctly. Before you make any clutch changes, it is
essential to make sure that the carburetor is clean and free from any varnish
build up.
If the snowmobile has been sitting for four months or longer
with fuel in it, we recommend that the carburetors be removed, disassembled and
soaked in carburetor cleaner. Each part should be washed off, then dried with
compressed air. Check each component (main jet, pilot jet, needle jet, etc.) to
see if the jets are correct for your altitude and riding temperature. The
floats must also be set at the correct height. Also, the needle and seat should
be checked by performing a "leak down a test" to insure that it holds pressure.
Your snowmobile dealer will need to perform this test because it will require a
special tool. If your snowmobile has dual carburetors, they must be
synchronized. Choke cables should also be checked to make sure they are working
properly. Your air box should be clean and free from any dirt of belt fiber.
Clutches
Both the drive clutch and the driven clutch should be
checked and inspected for wear. Trying to calibrate a worn out clutch is frustrating
as well as a waste of time. Belt fiber and dirt must be cleaned with compressed
air. The clutches should be lubed with a heavy duty silicone dry lube. Silicone
will not build up or attract dirt or belt fiber like petroleum-based
lubricants. If any components within the clutches are worn, they must be
replaced. Special areas of attention should include examination of the rollers
on the spider and the bushings in the cam arms in the drive clutch. Also the
helix wear pads within the driven clutch should be checked and/or replaced. If
the helix in the driven clutch is scratched from wear and tear, then they can
be polished in the contact area where the wear buttons slide with some 320
emery cloth. If your driven clutch has rollers, then they should be inspected
for wear, especially in the axle area where the rollers pivot.
Gearing
The most important component on the drive system is the
belt. A worn or stretched belt will destroy your performance. If in doubt,
temporarily install a new belt to see if your performance improves. Center to
center distance must be correct and clutch off set must be checked.
Within the chaincase of each snowmobile there is a set of
gears. Each season the chaincase cover should be removed. This allows the chain
and gears to be inspected. The oil should be drained out, the chain and gears
should be removed and inspected. The chain must be free of any kinks and should
not exhibit wear or broken links. Also, the gears should not have any clipped
teeth or noticeable wear on the teeth. If premature wear is found, they should
be replaced. While the gears are out of the chaincase you should count the
number of teeth on each gear and compare the ratio with your snowmobile
manufacturer's recommendations. Most high altitude setups include lower gear
ratios. A lower gear ratio allows your snowmobile to perform better due to the
horsepower robbing effect that is encountered at altitude. Lower gear ratios
also improve belt life in extremely deep powder conditions.
Drive Train
Power is transferred from the engine to the drive clutch,
from the drive clutch to the driven clutch then through the chaincase to the
drive shaft. The drive shaft turns the track. The track rides on a combination
of idler wheels and hifax. The point I am making is that as power is
transferred through each shaft and as each wheel or gear turns, it pivots on a
bearing.
These bearings are exposed to snow and the elements. Sooner
or later the bearings get rough and fail. Power is robbed by each bearing that
is marginal or that has failed. Each snow season the rear suspension should be
removed and each bearing and idler wheel should be checked and replaced as
needed.
Hifax should also be checked and replaced as needed. Another
power robbing factor could be a track that is out of adjustment. If the track
pulls to one side or the other, it will take more power to spin the track. Also
a track that is over tightened will rob power as well.
With the ACT Drive system Arctic Cat now uses in many of its
snowmobiles, that means some special attention needs to be paid to sleds with
that drive system. You should change the drive case oil every 500 miles if you
ride in deep powder or are an extreme mountain rider. If you mostly ride
trails, then changing the oil every 1,000 will suffice.
Chassis
The last area to discuss is the chassis. Adjustments can be
made to the front suspension for a correct toe in and toe out measurements. All
front end alignments should be adjusted to have about one fourth of an inch toe
out (meaning the front ski tips are wider than the back). This will keep the
snowmobile from darting. Toe in steering will rob power just as a downhill
skier will put his ski tips together (snow plowing) to slow down.
The position of your track in relation to the rear
suspension will give you more or less ski pressure. Dropping the front of your
skid frame down will give you less ski pressure and more traction for climbing hills
or going through deep powder. In reverse, if you suck your front part of the
rear suspension up into your tunnel, your track will be more oval shape and
take less horsepower to spin the track.
This set up may work well for speed runs. The point is that
there are many ways to set up your snowmobile's suspension. Adjustments are
available for you to fine tune your snowmobile and meet your specific riding
style. Performance is where you find it.
(ED-Cutler owns Cutler's Performance
Center in Orem, UT.
This is an excerpt from his book, Clutch Tuning Handbook, which offers lots of
information on how to keep your snowmobile running at its best for peak
performance. For a copy of the book, contact Cutler's at 801-224-5005. The book
retails for $19.95 and has 106 pages with more than 100 photos. For more
information on Cutler's, log on to www.cpcracing.com.)