Engine Rebuild

1985 RZ350

1985 California RZ350

My bike was on its original bore and had a hole in one piston so I decided to rebore both barrels and fit new pistons from Wiseco to each. A local guy in SF took care of the boring and ordered the correct size pistons to match.

Just to be safe I dropped a ring in the new bore....

..and pushed it down mid-bore with the new piston. I made sure the piston ring ends were on an area of the bore without a port opening....

..and measured the end gap with a feeler gauge. The upper ring should be between 0.30 - 0.45mm and the lower should be between 0.35 - 0.50mm. Both were right in the range.

I fit the piston rings be carefully opening them up just enough to slide over the side of the piston.

New gaskets were used on each cylinder and I was especially careful not to let anything fall in to the crank mouth openings.

For each cylinder, I fit the new caged needle bearing at the small end after rubbing some 2 stroke oil on it.

The piston needs to be installed in a certain direction. On Wiseco pistons an "L" should be pointing towards the exhaust port of the cylinder. I loosely fit the wrist pin on one side only...

..and then pushed it through the small end. On each side a wire circlip holds the pin in place. There is a small area removed from the wrist pin hole which helps to hook these out when replacing pistons in the future.Wrist pins can sometimes be stubborn so you can always dray them through with washers and a small threaded rod if required.

The cylinders where given a smearing of 2 stroke oil in their bores, then carefully the ring was compressed by hand and fed in to the cylinder.

Both cylinders installed without the barrels bolted down. I checked for any snags by rotating the crankshaft. Everything looked nice and smooth so I bolted the cylinders to the casing and moved on to the cylinder head. The manula notes a certain torque for these nuts but I found it impossible to get a torque wrench in the close confines of where the nuts sit so just did my best guess at making them all equal. This is also a good time to refit the small metal joint that connects the two powervalves so that operate from a single servo motor.

The cylinder head gasket is an odd thing made from two layers of aluminum. From everything I have read it is a very good idea to use only a genuine Yamaha gasket as pattern parts have a reputation of failing and destroying the motor with it.

The head is placed on the cylinders and then followed by the washers and nuts which I tightened finger tight.

The ten cylinder head bolts need to be tightened 1/2 a turn at a time in a special order so that the head is not warped. The order is cast in to the head casting but I have also noted it above. The bolts should eventually be torqued to20 ft/lbs .

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