Engine Rebuild

1985 RZ350

1985 California RZ350

The clutch is a pretty simple design. Basically the way the clutch works is that plain steel plates and plates with cork faces are stacked one after the other and held together by a clutch basket and clutch center. The plain steel plates have grooves in the inside that slide in the clutch center which is directly connected to the transmission and rear wheel. The cork plates have grooves that slide in the clutch basket which is directly connected to the crank. When the clutch spring pressure is removed by engaging the clutch the series of plates can slide by each other. When the pressure is slowly increased by releasing the clutch lever, the plates start to slide less and less past each other until the eventually rotate together

This section shows how to install a clutch on a bare transmission shaft. Please note that the kickstart idler gear/tachometer drive gear must be installed before installing the clutch.


The first item to put in place after the cases have been put back together is this bearing retainer. I use Loctite on both the screws just to be sure.

This is followed by bent piece of metal also installed with two screws and Loctite on each one.


Slide the flat thrust washer down over the spined shaft so that it sits flush against where the shaft leaves the casing.

Lubricate the transmission shaft and slide the grooved tube bushing over the main shaft and all the way down until it is against the washer.

Now the main clutch basket can slide over the grooved tube. This part of the clutch always spins when the motor is running but spins on the transmission shaft independently instead of spinning with it.

As you slide the clutch basket down on the shaft, be sure to look and make sure the small gear attached to the rear meshes with the free spinning gear on the casing. The free spinning gear is what drives the tachometer, and connects with the kickstart when you start the bike.

A small washer goes between the constantly spinning clutch basket and the clutch center .

Now the clutch center slides down on the transmission shaft. The inner hole of the center is splined to match the transmission shaft so they spin together.

A new tabbed washer should be fitted before the main nut. This stops the nut from ever coming loose. One tab of the washer fits in a small slot in the clutch center, and the other will be bent up over the nut.

Fit the main nut and just tighten it finger tight. From here, if you have the drive gears in place you and the top end isn't installed can use a con rod holding tool to lock the transmission or jam a rag between the primary gear and the outer clutch gear but...

....a very decent guy from the www.usa2strokers.com message board was kind enough to make me a clutch holder from an old clutch plate, and it worked perfectly. The nut should then be tightened to 65 ft/lbs.

Bend the flat tab over the nut face to lock it in position.

The clutch center has two rubber damper rings along with the plain and cork plates. The first of these rings goes on the bare clutch center before the first plain plate.

The first plain plate can go on in either direction but there is a small bump in the outside face (arrowed above) which should face up. Slide this plate down until it is up against the damper ring.

Then the second damper ring is installed directly on top of the plain plate.

Cork plates measure 3.0mm in width when they are new. If yours are less than 2.7mm they should be replaced. The damper ring is followed by the first cork plate. If the cork plates you are using are new, they should be soaked in SAE 10W30 motor oil before installing.

Now you can alternate with plain and cork plates until there are none left. As you place each plain plate make sure the machined bump in the outside edge is approximately 30 degrees clockwise from the previous one. There is no need to measure this - eyeballing it is fine.

The clutch is actuated by a rod which passes down the middle of the transmission shaft. It is a good idea to rub some motor oil on this before inserting it into the hole in the center of the transmission shaft.

This is followed by a ball bearing which goes in between the end of the rod and the actuating flange.

The actuator is placed next but won't be adjusted until after the clutch rebuild is almost complete.

The clutch cover can now be installed. There is a small arrow cast on the clutch cover and a corresponding arrow on the clutch center. Make sure these two arrows line up .

Before placing the springs loosely fit the washer and lock nut to the actuating flange. These can be tightened by hand for now as the final adjustment will happen after the springs are secured.

Check the springs before reinstalling them to see if they need replacing. New springs are typically 36.4mm in height and they don't need replacing unless they are less than 2mm shorter than new. Place a single spring in each recess and follow it with the retaining bolt. Tighten these by hand.

Tighten each bolt progressively so that you don't warp the clutch cover.

The final step is to adjust the clutch to disengage at the right point. Looking at the clutch arm on the casing you'll see there is a small point on the arm. When the clutch starts to disengage, this point should be in line with a similar point on the casing shown above. You can push the arm with your fingers and you'll feel the point where it no longer moves without serious pressure.

Now adjust the lock washer at the clutch center (this picture was taken when I was taking the clutch apart, so there were no springs). You should adjust it by loosening the nut so that the inner shaft with the Phillips head can be turned. Tighten the shaft to increase the free play and loosen it to decrease the free play. Keep checking the clutch arm on top of the casing to see when it is adjusted to where the arrows meet. Once it is adjusted tighten down the lock not to hold it in position. A drop of Loctite is also helpful to keep the nut locked.