Cam mod (YFZ450)

From Quad Hub Wiki

The cam mod, in regards to the YFZ450 engine, refers to retarding the timing of the exahuast cam by one tooth. What this does is brings the YFZ's timing to the same as that found in the YZ450F dirtbike's engine. Contrary to what Yamaha might say about this mod, it will not ruin your engine provided the mod is done correctly.

Performance

The majority of the effects of the cam mod can be felt in the mid to upper RPM range.

The idea behind the retardation of the exhaust cam has to do with the duration of maximum compression of the engine. Since the exhaust gas is not able to leave the cylinder as early, its expanding pressure is applied to the piston longer. This force is thus pushing downward on the piston a further distance resulting in an increase in work when compared to the same situation with stock timing. An increase in work done on this piston is translated to more torque on the crankshaft and thus more horsepower.

Tutorial

• Make sure the quad is clean of dirt, sand, mud, etc.
• Remove gas tank cover and side panel plastics.
• Turn off gas and disconnect the fuel line from the petcock assembly on the gas tank.

• Remove gas tank.

• Remove plastic gas tank shield.
• Disconnect ignition coil and both breather hoses from head cover.

• Remove spark plug.

• Remove both head cover bolts.

• Remove head cover.

• Remove both timing plugs on left crankcase cover.

• Remove chain tensioner cap bolt.

• Using a small flat head screwdriver, retract the chain tensioner by turning clockwise until it stops rotating.

• Rotate crank to top dead center.

• Remove camshaft cap bolts in stages in a criss-crossing pattern.

• Remove both camshaft caps. Be careful not to lose the clips underneath the caps.

• Take note that at top dead center before the cam mod, outer marks on camshafts both align with the top of the head.

• Retard the exhaust camshaft clockwise one tooth. This is done by wiggling the camshaft out to where there is enough slack in the chain for the teeth to retard one tooth.

• After the rotation of the exhaust camshaft, there should be a difference in the alignment of the marks on the camshafts. This will tell you if the mod has been done correctly.

• Replace the camshaft clips and caps back over the camshafts. Remember to be careful not to lose the clips.
• In the same pattern as before, screw in the camshaft cap bolts in stages. (Torque: 10 Nm, 7.2 ft·lbs)
• Release the chain tensioner by beginning to screw it counter-clockwise and then letting it freely turn itself until it stops.
• Rotate the crank a few times to ensure that everything is still rotating freely.
• Replace chain tensioner cap bolt. (Torque: 7 Nm, 5.1 ft·lbs)
• Replace head cover and secure with head cover bolts. (Torque: 10 Nm, 7.2 ft·lbs)
• Replace spark plug. (Torque: 13 Nm, 9.4 ft·lbs)
• Reconnect ignition coil and both head cover breather hoses.
• Replace timing plugs.
• Replace gas tank.
• Reconnect fuel line to petcock on gas tank.
• Replace gas tank cover and side panel plastics.

Once the mod has been fully completed, a rejet is suggested.

External Links

• Step-by-step Cam mod tutorial on YFZCentral written by Terse
• Video series of the mod done by Dogriders
  • Removing plastics
  • Removing cam tower
  • Setting top dead center
  • Marking the cams
  • Removing chain tensioner
  • Removing cam journals
  • Cam mod