De nada, amigo. Thank you for your kind words. ;)

Here is another tip. ;)

The cam sprocket also has a dot in addition to the "L" and "R" markings on the camshaft sprocket. You can see this dot at the 11 o'clock position in the photograph below.

http://i.imgur.com/44aWUf6.jpg

When you install the timing chain on the cam shaft, try to place this dot even with the top of the cylinder head on the right/intake side of the cylinder head. When placed in this manner, the "L" and "R" markings will be placed in the correct vertical locations. If you are satisfied with this alignment, you can apply some black RTV silicon to the cylinder head, and begin the final installation of the rocker cover. ;)

Wonderfully comprehensive tutorial! Of course, I focused on how you welded extensions onto the center stand; have you started a thread about your welder?


I also liked the idea of making a board adapter for your floor jack. I'm going to borrow that mod. :D


Have you considered non-stock valves? Perhaps there are stainless valves that would fit this engine.

Thank you, Weld.

Regarding the welding, I must confess I got lazy. I should have posted, "I coaxed my good friend Andy to weld some extensions onto the center stand." :lol: I will go back and correct my post. ;) I did a little stick welding back in the 90's, but I need to get that Eastwood welder you recommend. :tup:

The board adapter works very well. It provides a nice, wide and stable platform for lowering, and raising the engine into place. I used it to remove the stock engine, and install a Yamaha XT225 engine in my Zongshen Sierra. The adapter worked equally well with the NC250 engine in my RX3.

I have not confirmed any other valves which fit the NC250 engine. Of course, the problem might also reside with the valve seats. :shrug: So far, the valve clearances are holding. :tup: I hope the new valves and cylinder head have solved the problem.

Incidentally, I also installed four, new valve springs during this engine work. The cam chain was in very good condition, and did not exhibit any elongation, as the timing marks aligned perfectly. :tup:

Great write-up Spud! Excellent and complete, as always.

I remember back in the 70's, when unleaded fuel first came out, it was eating up the valve seats and the manufacturers had to go to hardened valve seats. I wonder if this is what's happening here?
Did the old valves look worn or just the seats?

You're welcome, JB.

My exhaust valve clearances did not stablize until about 16,000 miles. :shrug: I have never used an inspection camera. Could an inspection camera be employed in this situation? I suspect the size of the spark plug hole, the small area area inside the cylinder, et cetera, might cause problems for an inspection camera. However, I don't know. :shrug:

I suggest you talk to Gerry at CSC and tell him your maintenance record of how often you did each valve lash check, and the required adjustments. As with me, he might tell you to have a leak down test performed. I bought an OTC 5609, Cylinder Leakage Tester Kit, shown in the link below. It does an excellent job, and I highly recommend it.

http://www.tooltopia.com/otc-tools-5...FQsuaQodCX8J6g

http://www.usatoolwarehouse.com/Merc...1/otc-5606.gif

However, be forewarned. Even if your engine passes a leak down test, you still might have valve recession. My cylinder did not leak, but the valve recession was obvious from a visual inspection.

Once again, I would call Gerry at CSC and ask for his advice. If you, or anyone else has this problem, he should try to resolve the issue before his warranty expires. That is why I talked to Gerry several times about this problem, and performed a leak down test last fall. This gave me enough time to get authorization to tear down the engine, find the problem, and fix the problem before my warranty coverage expired. Based upon my experience with this problem, I decided to post this thread as a service to the RX3 community.

Thank you, 2LZ.

Since the valve recession was obvious, I didn't remove any of the valves for inspection. I wanted to ship the untampered cylinder head to Gerry for his inspection. I also didn't care to do the extra work. ;)

Is unleaded fuel required in China? I don't know. :shrug: If the Chinese are still using leaded fuel, you might very well be correct. ;) I remember reading somewhere that the Italian company, Piaggio, designed the NC250 engine. I suspect the Italians designed the engine for use with unleaded fuel. :shrug:

I'm hoping my experience with this problem is a rare exception. However, I felt an obligation to warn others who might be experiencing the same problem.

If you drop the engine for repairs, be sure to examine the O-ring which seals the intake manifold. Make sure this O-ring is not flattened, deformed, or torn, et cetera. Also, be sure this O-ring is installed when you tighten the intake manifold to the cylinder head.

http://i.imgur.com/xhwDOfN.jpg

This O-ring is a critical component which keeps dust from entering the cylinder head. Dust entering the cylinder head from either the intake manifold or air filter will eventually cause valve recession of the intake valves.

Once again, I recommend you keep your air filter well oiled, and clean. I use Belray Foam Air Filter Oil for the flat air filters in both my Zongshen motorcycles.

https://www.rockymountainatvmc.com/p...air+filter+oil

https://images.rockymountainatvmc.co...fil_oil_1l.jpg

Here is another tip. ;)

On all my other motorcycles, I always install the piston on the connecting rod first. Then I lower the cylinder onto the piston, while compressing the piston rings. I tried using this method with the NC250 engine, and it did not work. The piston rings of the RX3 are very difficult to compress, and I actually snapped one of the piston rings as I tried to lower the cylinder onto the piston. :wtf:

Therefore, I ordered another, complete set of piston rings, and used the alternative method of installing the piston into the cylinder first. ;) Here is a summary of that method.

First of all, install a circlip into one side of the piston. Using this method, you will only need to wrestle with a single circlip when the cylinder is resting over the engine case. ;) Then install the new piston rings in the piston. Apply motor oil to the piston rings and the piston skirts. I also spread a little oil inside the cylinder.

Turn the cylinder upside down on a workbench, and turn the piston upside down, making sure the arrow on top of the piston is facing the exhaust side of the cylinder. Using this method, it is very easy to compress each piston ring and push the piston into the bottom of the cylinder. :tup: Push the piston into the cylinder, but leave enough room at the bottom to install the piston pin later. ;)

Make sure you install a new cylinder base gasket on the engine crankcase before you install the cylinder/piston assembly.

Take the cylinder/piston assembly to the engine. Tilt the engine to the left, so the cylinder will not easily drop onto the engine case. Now you can install the cylinder/piston assembly over the cylinder bolts, and lower it to the proximity of the connecting rod.

Apply oil to the piston pin, and insert the piston pin through the piston and the connecting rod until it bottoms on the single circlip you installed earlier. Stuff a rag around the connecting rod so you don't accidentally drop the final piston circlip inside the engine. :wtf: Install the final circlip. Now you can remove the rag surrounding the connecting rod. ;) Finally, push the piston farther into the cylinder, and lower the cylinder onto the engine.

This method is very easy to perform while the engine is removed from the frame, and I might try using this method on my other bikes in the future.

Your suspicion is correct.

I tried to use my borescope to no avail.....sparkplug hole too small for access.

Got a better view with a LED flashlight and eyeballs.

Your expertise and willingness to share it, is certainly an asset to all RX3 owners.

And an asset to CSC.....you should be on the payroll.... :)

However, I would wager that when buyers signed up for a "user maintained" motorcycle, they didn't think that included removing the engine, and rebuilding the top end.

jb

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. :shrug:

http://i.imgur.com/HZRySJY.jpg

Thanks for your kind words, JB.

I'm hoping my experience with this valve recession is a rare occurrence. However, when you mentioned your valve clearances had not stabilized, I felt a moral obligation to warn you, and others, of the possibilities.

I think you might be having other engine problems. I also believe you have some time left on your warranty. I suggest you contact CSC and ask them to help you resolve these issues. If you were nearby, I would certainly help you with the engine work myself. Unfortunately, you live about as far away from Idaho as possible.

If anyone wants to purchase a Cylinder Leakage Tester Kit, I highly recommend the OTC 5609. Most leak down testers don't have a spark plug adapter which fits the 10 mm, spark plug hole of the RX3. :wtf: Also, this spark plug adapter must be small enough to fit in the narrow, spark plug hole of our RX3 motorcycles. Finally, if the hose comes off the adapter when you try to remove the spark plug adapter, you must be able to retrieve the adapter from the spark plug hole. If this last scenario occurs, you can use the spark plug wrench included with the RX3 tool bag to retrieve the adapter included with the OTC 5609 unit. :tup:

The OTC unit is well manufactured, works very well, and is sold for a very reasonable price. This tool also includes a very rugged, molded plastic case. The OTC 5609 works superbly with the RX3 motorcycle, so I highly recommend this unit.