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Posts : 859
Join date : 2010-11-05
Location : Englishtown, New Jersey

PostBlackScorpion on Sat 13 Nov 2010, 9:31 pm

Detailed guide to removing and installing the camshaft on a GY6. Covers valve timing, valve adjustment, and finding top dead center.

GY6 Camshaft Installation Guide                                                        [You must be registered and logged in to see this image.]

Camshaft Install Instructions

A. Before installation
1) Wash the entire buggy. This will keep dirt from falling where you don�t want it while the engine is exposed.
2) Remove the passenger seat from vehicle.
3) Make sure the engine is cold.

B. Access Camshaft assembly
1) Loosen the intake tube at the carburetor and remove the airbox and tube assembly.
2) Remove black plastic fan shroud from passenger side of motor. (Seven 8mm screws/bolts)
3) Remove carburetor and air intake boot from motor as a unit and place on a clean surface. Force may need to be applied to remove intake boot from engine if it binds. (Two 10mm nuts)
Note: Fuel line will need to be clamped to avoid dumping fuel.
Note: Insert a small clean rag into the intake hole to keep dirt from falling into the engine.
4) Remove plastic shroud from top of motor to gain access to cam chain tensioner. The lower shroud does not need to be removed.

Finding Top Dead Center
What is TDC? Top Dead Center refers to the piston being at the very top of its travel in the cylinder. On a four stroke, TDC will occur at the top of the compression stroke and the top of the exhaust stroke.
5) Remove sparkplug.
6) Move Flywheel until (T) mark is aligned with the arrow mark on the engine case.
7) Loosen four valve cover bolts and remove the valve cover.
Cool Now that you are inside the valve cover, rotate the flywheel until the cam is at the TDC position with hash marks aligned straight across the valve cover surface and the large TDC hole at the top of the cam gear. (Large TDC hole should be pointing directly towards seats)
Note: Document TDC on the flywheel using permanent ink; reference your mark to a point on the engine case.

C. Remove Camshaft
1) Remove the cam chain tensioner by removing the 2 bolts that secure it to the cylinder. Unless you have a spare, you will need to reuse the gasket. Use a razor blade to properly separate the gasket from the tensioner.
2) Remove the 4 head bolt nuts from the rocker tower and remove it.
3) Remove cam chain by tipping the cam gear downwards.
Caution: Be sure not to drop the cam chain down into the case. The case may need to be split to refit it.
4) Secure the cam chain with a cord or rope tied to a part of the chassis so it can be accessed on reassembly.

D. Reassembly
1. Insert the new cam by again tipping the cam gear down and attaching the cam chain making sure the alignment is set to the mark you made on the flywheel and the hash marks on the cam, with the large cam hole pointing at the seats.
2. Install the cam tower back onto the cylinder studs with the EX towards the exhaust valve (downward).
3. Install the head stud nuts and torque to 1st 16 lbs then on to 25 lbs using a cross pattern.
Note: The Yerf Dog manual states 16lbs on these nuts, however they come from the factory tourqed to 25lbs.
4. Recheck the cam alignment chain to ensure the cam is in the correct position to the mark you made on the flywheel.

Cam Chain Tensioner.
5. Release the spring tension on the cam chain adjuster by removing the screw cap and turning the adjuster inside using a small flat blade screwdriver clockwise until it stops. This will remove all tension from the adjuster.
6. Insert the adjuster and tighten the 2 mount screws while holding the 0 tension on the adjuster.(Make sure gasket is in place.)
7. Turn the adjuster back to full tension (rotate counter-clockwise, will rotate on its own) and reinstall the cap screw.
Caution: Failure to release the tension on the Cam Chain Adjuster during reassembly will damage the cam chain beyond use. (The cases must be split to replace the cam chain.)

Adjusting the Valves.
1. Adjust the valve tappets using a feeler gauge to a clearance of :
Intake- .002- .004 � Exhaust .003-.006�
Note: Printer paper happens to be 0.003� Smile
Note: Valves must be adjusted on a COLD engine.
Note: Adjust valves with engine at at TDC.
2.Loosen the 9mm valve tappet lock nut and turn the tappet out several turns
3.Sandwich your feeler gauge between the bottom of the tappet (adjuster screw) and the top of the valve
Note: Feeler gauges are thin pieces of metal which are a predetermined thickness.
4.Tighten the tappet while moving the feeler gauge back and forth until you can feel a slight drag on the feeler.
5.Tighten the lock nut with the feeler in place.
6.Ensure the gap is still within proper range by sliding the feeler back and forth again.
7.Repeat step 2 - 6 for remaining valve.

E. Final Assembly and Inspection.
1. Rotate the assy several times by turning the flywheel then recheck the TDC-Mark to Cam alignment.
2. Reinstall all remaining assemblies in the reverse direction of disassembly.
3. Check operation of motor. ( Does it start and idle?)
4. Check jetting and set as required by intake, exhaust and cam use.

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