Steahly Flywheel Installation Instructions for YZ 250 2002 and newer
Carefully read these instructions before you begin installing the flywheel weight. If you do not have the
mechanical abilities or proper tools then get some help. If the flywheel weight is not installed and maintained
according to these instructions it could result in engine damage and/or a serious crash.
1. Remove the ignition cover from the left side of the engine. Try not to tear the gasket. Check your main
bearings for wear by lifting up and down on the ignition flywheel. If you feel any movement you may need
to replace your main bearings before installing a flywheel weight.
2. Remove the flywheel nut turning it counterclockwise. You will not be reusing the nut with the flywheel
weight. Use one of the ideas below to keep the flywheel assembly from turning when you loosen the nut.
Some of these methods could cause damage if you are not carefull.
A. Use a Steahly Engine Lock Up Tool, part number E-3, for most two strokes up to 380cc. It screws
into the spark plug hole and the piston hits the plastic tip, which stops the flywheel rotation.
B. Use an air powered impact wrench to quickly spin the nut loose. However, this will not allow
acquarate torquing when tightening the flywheel weight.
C. Remove the spark plug and bring the piston up to about one inch from top dead center. Feed in a
few inches of rope (leave some hanging out so you can pull it back out). Make sure that the rope
does not go into any of the cylinder ports. Now slowly turn the engine over compressing the rope
between the cylinder and the head until the flywheel stops turning. Use only smooth torquing
action while loosening and tightening nuts. Do not use hammers or breaker bars.
D. Put the transmission in high gear and hold the rear brake on. Be careful, if you get too rough you
could break your brake caliper bracket.
3. Remove the washer that is underneath
Special Tool
Crankshaft End
Stock Flywheel
the flywheel nut, if there is one. NEVER
use the stock washer with your
flywheel weight.
4. Check the end of the crankshaft to
make sure it is not bent, the end is not
flared out, and that the threads are not
damaged.
5. Check the set screws in the flywheel
weight to make sure they are not
sticking out on the inside of the weight.
Never remove the set screws from
the outside of the weight, the screw
holes have been staked (punched with
a special chisel) to prevent them from
coming out.
We recommend that you do not use
thread lock compound (Loctite) on the
Flywheel Weight
Set Screw
1/4 Inch Bolt
set screw threads because it may cause
them to seize, instead we use anti-seize
or grease.
6. Bolt on the special tool to the outer face of the flywheel
weight using the two ¼” bolts.
7. Install the flywheel weight by screwing it clockwise onto
the end of the crankshaft. It should screw on easily.
Make sure it makes solid contact against the ignition
flywheel at the same spot where the stock nut makes
contact. Use a ½” drive torque wrench to tighten the
flywheel weight to the manufacturer’s recommended
specifications for the stock flywheel nut. YZ 250 2002
torques to approximately 27 foot pounds. YZ 250 2003
and newer torques to approximately 42 foot pounds.
8. Bend the clutch arm with pliers to the right to make
about 3mm (1/8 inch) clearance between the flywheel
weight and the clutch arm.
9. Remove the special tool and two ¼” bolts. Keep the special tool in a safe place in case you need to
remove the weight at a later date.
10. Screw in the four set screws and tighten them by working back and forth diagonally (like torquing a head)
until they are all equally tight. It is very important to recheck the set screw tightness after the first
½ hour of riding and on a regular maintenance schedule of about every 8 to 10 hours of riding.
Some bikes have to be checked more often than other bikes depending on vibration and other factors, so
check them often until you get a feel for it.
11. Install the ignition cover using the stock gasket. The 13 ounce weight (part number 825H or 826H) must
have two gaskets under the ignition cover (one gasket should be supplied with the 13 ounce kit).
12. Maintenance – A smart rider checks all of his nuts and bolts regularly, so make checking your flywheel
weight and tightening your set screws part of your regular maintenance, it only takes a minute. While the
cover is off wipe out any dirt and moisture and give the weight a little shot of corrosion preventing oil such
as WD-40. If you do a lot of huge jumps, that is going to prematurely stress your flywheel weight (along
with everything else on your bike) and you should check it more often and be aware that it may shorten
the life of your flywheel weight.
Troubleshooting
Increased vibration – First be sure that it is actually vibrating more than it did before, it may be that you are
just more conscious of vibration. If you are sure that it is vibrating more than before check your main bearings
for wear and your crankshaft for a bent or damaged end. If everything checks out you may need to send the
weight in for inspection.
Rubbing on cover – The YZ ignition cover is plastic and can easily warp. If your cover is warped you may
need to replace the cover, add an extra gasket or grind a little material off the inside of the cover. The plastic
cover can also get pushed in momentarily when you fall or hit something, so you may have some scuff marks
inside the cover even though it does not usually rub. Heavy rubbing or the cover not fitting at all is usually
caused by failing to remove the stock washer as described in step 3 or you have an aftermarket cover (which
are usually metal). If you have an aftermarket cover you can purchase a cover spacer from us. Also make
sure you have the right flywheel weight for your year and model of engine and make sure that you have the
stock ignition.
WARNING: This product will change the power characteristics of your engine. Adding flywheel weight
results in smoother, more tractable power delivery by causing the engine to rev less quickly (slower increase
in engine RPM). If your engine has low power because of engine wear, lack of maintenance, improper jetting,
engine modifications, or any other reason, adding flywheel weight could exaggerate the problem causing
bogging or hesitation. Use caution when riding until you are fully familiar with the power changes.
Guarantee – Since we have no control over installation, application, or use of our flywheel weights they
are sold as is. No warranty is expressed or implied. Steahly Products Inc. may, at our discretion, repair or
replace a flywheel weight that we believe is defective, however, our liability extends only to the flywheel
weight and does not in any event include incidental or consequential damages. If you have a problem or
installation questions give us a call, we may be able to help.
Satisfaction – If you are not completely satisfied with the effects of the added flywheel weight we may be
able to work with you by customizing your flywheel weight to better suit your needs. There are many variables
that may affect the amount of weight that may be perfect for your needs. Individual rider preference, riding
ability, type of terrain, and engine modifications are some of these variables. If you feel that the Steahly
Flywheel Weight is too heavy we may be ably to remove some of the weight for a small fee. Some models
can not be lightened, so call first to discuss your individual needs.
1-800-800-2363
Steahly Off Road Products Inc.
3850 Pioneer Rd, Medford, OR 97501, USA
541-535-4896
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