Tech Tips!

by Jonathan Teraji

 YSR Top End Assembly and Break In

Assembly:Wrap a clean rag around the connecting rod, making sure to fill in area over crankshaft. This is to prevent any foreign objects (like the circlips!) from falling down into crankcase. Install rings on piston. There are two types of pistons, follow instructions for the type you are using.

Yamaha Piston: Expander ring goes on the bottom ring land. Make sure opening in all rings straddles the ring locating pin on the ring land. The other two rings look identical.... they are not! After installing on the piston make sure they expand and contract freely. If they do not, swap the two rings. Check for free movement. This may sound confusing but you basically have a 50-50 chance of getting it right the first time. And, it must be right or the piston and rings will not function properly.

Wiseco Piston: The rings are identical and there is no expander ring.


Note: rag is wrapped around rod, long nose pliers used to gently compress circlip to fit in slot, rings are straddling ring locating pin

Install new wrist pin bearing on the rod. Use a drop of oil on bearing and rotate to spread on inner race of rod.

Install one circlip. Make sure it seats in the groove properly. Orient the “ear” on the circlip, (or in the case of the wiseco circlip, the opening), to the 6 o’clock position. Slip piston over small end of rod. Install the wrist pin. Install the second circlip. (Make sure the arrow on top of the piston points towards the exhaust.)

Remove rag that is protecting crankcase, and install cylinder base gasket.


Proper Ring Orientation

Immediately before installation of the cylinder, wash the cylinder with dishwashing soap and water. Scrub all the ports and the bore. Rinse thoroughly. Dry thoroughly with a lint free cloth. Make sure cylinder is both dry and clean.

Do Not smear oil in the cylinder. It wants to be installed “dry.”


One hand compresses rings, other slips cylinder on

Slip the cylinder over the piston with one hand while compressing the rings with the other hand. Make sure ring ends are straddling the ring locating pin on the piston ring land. Rotate crankshaft and make sure piston moves up and down freely. Install head gasket. (Head gasket has a raised ridge. It goes up.) Install head. Torque head nuts to 9-ft lbs. using a cross pattern. (If you are using the oil injector, don’t forget to hook up oil line and bleed the pump!)

Break In:

Do not ride at a sustained RPM for a long time.

Operate bike in “normal” manner. Ride for 5 minutes. Turn off and let cool down for 5 minutes. Then ride for 10 minutes and the turn off and cool for 5 minutes. Continue this adding 5 minutes of run time until you reach 30 minutes. Bike is then broken in. (This procedure takes time and patience. When done properly the rewards are great.)

It is important that during this break in time the RPM is varied constantly. Do not run at a sustained RPM for a long time. If you are cruising at 35mph for a minute, change to 40mph, etc. Do not put on a stand and let idle for any part of the break in period. Engine needs to have air going past it and the RPM constantly varied.


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