RX3: Engine Top End Rebuild at 22,450 Miles

[SpudRider]

Valve recession occurs when the face of the valve recedes into the valve seat in the cylinder head. If not corrected, the valve face and valve seat will continue to erode until the valve leaks, and damages the cylinder head.

Valve recession can be caused by several factors. If you don't regularly oil and clean your air filter, dirt can enter the engine and cause valve recession. A leak in the intake manifold can also allow dirt to enter the cylinder. Defects in either the valve face or the valve seat can also cause valve recession. Since I have always properly maintained my air filter and I did not find an leaks in the intake manifold, I must assume the valve recession in my engine was caused by a manufacturing defect. Hopefully the new cylinder head and new valves have corrected this problem. As always, I appreciate the excellent warranty coverage I received from CSC Motorcycles in Azusa, CA.

The exhaust valves in my engine finally did stablize after about 16,000 miles. I did notice damage on the exhaust lobe of the camshaft. I replaced the camshaft during the engine rebuild.



Both of the roller rockers were in good condition, so I did not replace them.

[SpudRider]

In order to rebuild the engine, it must be removed from the frame of the RX3 motorcycle. With a center stand installed, removal of the engine is pretty easy. Installing a center stand greatly facilitates repairing flats on the road, or trailside. For this reason alone, it is a good idea to purchase a center stand from CSC motorcycles. Removing and reinstalling the engine would be much more difficult without a center stand.

Since I have modified my RX3 with a 21-inch front wheel, I needed to place a piece of 2x8 lumber under the center stand to loft the wheels. After the engine rebuild I coaxed a good friend to weld two extensions onto the center stand.



You do not need to remove the luggage in order to remove the engine from the frame.

Since the swingarm bolt must be removed before you can remove the engine from the frame, you must first remove the swingarm from the motorcycle. To make matters easier, I also decided to remove the rear wheel, lower shock linkage and shock absorber before I removed the engine.

[SpudRider]

Before removing the engine you must disconnect the clutch cable and all electrical connections from the engine. You must also remove the upper and lower engine guards, exhaust manifold, et cetera. I will post several step-by-step instructions for the engine rebuild later in this thread.

After removing the perimeter frame beneath the engine, you are ready to remove the engine bolts and lower the engine. I supported the engine on my 3-ton Husky jack before I loosened the final engine bolts, removed the swingarm bolt, and lowered the engine.

Several years ago I made a wooden board attachment for my Husky jack. This wooden board makes it easy for me to support the engine during engine removal and installation. I used this wooden attachment to remove and replace the engines in both my Zongshen ZS200GY-2 (Sierra), and my Zongshen RX3.

[jbfla]

Spud,

Do you know what caused the scoring of the cam lobe in the photo?

Originally Posted by SpudRider

.........

jb

[SpudRider]

Originally Posted by jbfla

Spud,

Do you know what caused the scoring of the cam lobe in the photo?

jb

No, I do not know what caused the scoring. The roller rocker was in good condition. The associated rocker is on the right side in this photograph; it is the exhaust lobe rocker.

I did not notice any valve recession of the exhaust valves. Perhaps it required 16,000 miles for my exhaust valve clearances to settle because of the wear on the camshaft exhaust lobe.