Zongshen 200GY-2: Engine Rebuild at 51,687 Miles

[SpudRider]

My Zong was burning a lot of oil, and I noticed an ominous sound coming from the cylinder head. 8O Therefore, I disassembled the top end of my Zong's engine to determine the cause of the noise.

I discovered the exhaust valve rocker of my Yamaha, XT200 cylinder head was worn. To verify the cause of my Zong burning oil, I took the cylinder to my machinist to have him measure it with his bore gauge; it was well worn. Therefore, I decided to have the machinist rebore the cylinder to 1.00 mm oversize.

I had the machinist blast the carbon deposits from my cylinder head. My old valves and valve seats were in good shape. However, I already had some new, Zongshen valves, so I decided to install them. To repair the damage to the exhaust valve rocker, I ordered two new rocker arms and a new camshaft from Taobao. I also ordered new, TW200, valve stem seals. In addition, I ordered a new, automatic cam chain tensioner from Taobao.

I ordered a 4th oversize, Yamaha, TW200 piston and piston rings. I ordered a new piston pin from Taobao. I already had a new pair of Zongshen circlips for the piston pin. I also ordered a complete gasket set and a new, cam timing chain from Taobao.

Spud

[SpudRider]

On Saturday I removed the left crankcase cover to install the new cam timing chain.



Previously I had purchased a flywheel holder from eBay. After attaching the flywheel holder, I used my breaker bar to remove the flywheel bolt.



After the flywheel bolt was removed, I used my TW200 flywheel puller to remove the flywheel from the crankshaft.



After removing a woodruff key, the starter wheel gear and its associated washer, I gained access to the cam timing chain. After inspecting the cam chain guide, I removed the old cam timing chain, and installed the new one.



I replaced the washer and the starter wheel gear. Next I replaced the woodruff key. I replaced the flywheel/magneto, and torqued the flywheel bolt to 36 foot-pounds.



Spud

[SpudRider]

Now I turned my attention to the new piston. After installing the piston rings in the piston, I dipped the top of the piston in engine oil. I also oiled the new piston pin. I installed a circlip in one side of the piston, and installed the piston on the end of the connecting rod. With the piston in place, I installed the second circlip holding the piston pin.

I lubricated the inside of the cylinder with oil. After installing the new cylinder gasket and O-ring, I lowered the cylinder onto the piston, and installed the second chain guide.



Checking my mailbox, I was pleased to see my TW200, valve stem seals had arrived. Therefore, I now turned my attention to the cylinder head.

Spud

[SpudRider]

Previously, I had lapped the new valves to the valve seats. I now installed the new valves and the new, valve stem seals. Using my valve spring compressor, I completed installing the valve assemblies.

Next I installed my new rocker arms, taking care to lubricate them with moly-oil, a combination of molybdenum grease and engine oil. Next I installed the new camshaft, and adjusted the valves to Yamaha specifications. The refurbished cylinder head was now ready to install, but daylight was fading, so I decided to complete the assembly on the engine on Sunday.



Spud

[Weldangrind]

Terrific pics and write-up, Spud.

Slick flywheel holding tool; was it very spendy? I've never used a tool like that, only an impact. The downside is that you can't accurately torque the bolt with an impact.

Are you performing the bearing mod on the cam?

[SpudRider]

Originally Posted by Weldangrind

Terrific pics and write-up, Spud.

Slick flywheel holding tool; was it very spendy? I've never used a tool like that, only an impact. The downside is that you can't accurately torque the bolt with an impact.

Are you performing the bearing mod on the cam?

Thank you, Weld.

The flywheel holding tool was very inexpensive. It makes the job much easier, and allows me to use the exact torque values set in the service manual.

I did not perform the cam bearing mod. However, I added a lot of new parts to my Zong. I finished the top end rebuild today, and the bike runs great! I plan to post the rest of my rebuild details and photographs later tonight.

Spud

[SpudRider]

On Sunday I finished the top end rebuild of my Zong’s engine. Here’s a photograph of my Yamaha, XT200 cylinder head, ready to be installed on my Zongshen cylinder. As I said earlier, I had my machinist blast the carbon from the cyclinder head. I also installed new, Zongshen valves. Lapping the the new valves with the cleaned cylinder head was a very easy job.



The machinist also blasted the carbon from the exhaust and intake ports, which was very nice.



Here’s the end of my new, Zongshen camshaft, ready to accept the cam sprocket after the cylinder head is installed.



After installing the 3 dowels in the cylinder head, I installed a new O-ring around the dowel which contains the internal oil line to the cylinder head.



I then installed the Zongshen, tri-metal, cylinder head gasket.



After threading the new, cam timing chain through the cylinder head, I installed the cylinder head. I oiled the copper washers and cylinder head flange bolts, as specified in the TW200 Service Manual. I torqued the flange bolts to 16 foot-pounds, in two steps. Then I torqued the cylinder head socket bolts. Finally I torqued the two cylinder bolts which also secure the clutch cable holder.



After setting the flywheel to top dead center (TDC), I threaded the cam timing chain around the cam sprocket, and aligned the index mark to the cylinder head. I always enjoy getting this job done, since I no longer need to worry about dropping the cam chain down into the engine! :roll:



With the cam sprocket properly indexed to TDC, I torqued the cam sprocket bolt to 43 foot-pounds, using my flywheel holder to secure the flywheel. I love this inexpensive flywheel holder I purchased from eBay!



My stator and pickup coil appeared to be in excellent conditon, and this visual inspection was confirmed by correct resistance readings I obtained from my digital multimeter. Therefore, I felt confident to re-install the left crankcase cover.



I installed a new, TW200 gasket to the left crankase before I re-installed the left crankcase cover.



My Zong’s engine was now completely reassembled! I had previously set the valve lash on the work bench. However, I now checked the valve lash once again, after the engine had been completely reassembled.





Here’s a partial view of one of my new, Zongshen valve rockers.



After rotating the crankshaft and camshaft a few times, the valve lash was a little tighter. Therefore, I adjusted the valves a little looser to the middle of the specifications. Since the engine was now completely reassembled, I immediately added 1 quart of Mobil Delvac, 15W/40 diesel oil to the crankcase, lest I forget!

Spud

[SpudRider]

Although it still worked well, my original, automatic, cam chain tensioner was a bit worn after 51,687 miles.



Therefore, I decided to replace it with a new, Zongshen tensioner I had bought from Taobao.





With the valve lash set and engine oil in the crankcase, I attached the top, engine mounting plates, the valve rocker covers, and the cam sprocket cover.



The engine’s top end rebuild was now truly complete. However, I still needed to re-install the carburetor and the exhaust system.

Spud

[SpudRider]

I hate re-installing the carburetor in a motorcycle, and I particularly hated re-installing the carburetor in my Zongshen 200GY-2. :( The Zong’s carb is notoriously difficult to install because the air boot from the airbox to the carburetor is extremely stiff, and short. The boot is stiff because it is manufactured from the same, tough plastic as the air box itself! 8O After wrestling with the air boot for about 30 minutes, I had finally had enough! :evil: Last year I had bought an air boot for the Yamaha TW200, but I wasn’t sure it would fit without modification. On Sunday I decided I would make it fit, because I never again wanted to wrestle with the Zongshen air boot! :evil: Without too much difficulty, I pulled the Zongshen air boot from the bike’s air box.





Even though the plastic is extremely tough, you can see where I had gouged it in previous attempts to make it fit on the carburetor’s intake! :roll: Now I compared the TW200 air boot to the Zongshen air boot.

The TW200 air boot is made from a very nice, strong, yet flexible rubber. However, I didn’t know if the boot would fit the hole in the Zongshen airbox. :roll: Also, the TW200 air boot was longer than the Zongshen air boot, but I appreciated this difference, since the Zongshen air boot seemed to be too short.



I was now committed, so I went to work installing the TW200 air boot into the Zongshen air box. :roll: Much to my surprise, relief, and pleasure, the TW200 air boot fit perfectly! Here’s a view of the air boot from the inside of the Zong’s air box.



Here are views of the newly installed, TW200 air boot taken from the left and right sides on my Zongshen motorcycle.





The outside appeared to line up perfectly! It was time to try installing the carburetor. Once again, I was extremely pleased to discover the TW200 air boot was a perfect fit. Instead of wrestling with the infernal, Zongshen air boot, my Teikei carburetor installed easily, and perfectly, without any stress!





I have made many modifications to my Zongshen 200GY-2, but the TW200 air boot is definitely one of my favorite modifications to this bike! I had always dreaded working on my Zong’s carburetor, but that dread has now vanished! I strongly encourage all Zong owners to pull out the Zongshen air boot, and replace it with a TW200 air boot.

Spud

[SpudRider]

After the previously dreaded, carburetor installation was completed, I quickly installed my exhaust system. However, after installing my fuel tank, I noticed my fuel line was leaking. :roll: My old fuel line was stiff and discolored, so it was obviously time to make a trip to the local O’Reilly Auto Parts store. I purchased 2 feet of 3/16-inch, clear fuel line for $2.29. Here’s a photograph of the old fuel line juxtaposed with the package of new fuel line.



After installing the fuel line, my trusty Zong started easily, and I verified oil flow to the cylinder head. I now installed a new CDI unit I had bought from Taobao, since the old CDI unit had been acting a little flaky. :roll: After re-installing the side covers and saddle, the entire job was complete. I went for an 83-mile ride, and the engine performed superbly! I hope my Zong will continue to run well for another 25,000 miles or so before my next engine rebuild.

Spud

[MICRider]

Sweet writeup with beautiful pictures as usual Spud . I'm sure you'll have no problem at all putting another 25,000 smiles on the old Zong, truly an incredible bike!

[Weldangrind]

I might have to pick up a flywheel holder like that.

My original TW airbox boot looked just like your original Zong boot; it shrunk over 3/4"! Even with a new boot, mine was a bit of a struggle to install, as if even the new boot is 1/4" too short.

I'm kinda surprised that you didn't paint the cylinder and head while they were off.

[SpudRider]

Originally Posted by MICRider

Sweet writeup with beautiful pictures as usual Spud . I'm sure you'll have no problem at all putting another 25,000 smiles on the old Zong, truly an incredible bike!

Thank you, Stew.

Spud

[SpudRider]

Originally Posted by Weldangrind

I might have to pick up a flywheel holder like that.

My original TW airbox boot looked just like your original Zong boot; it shrunk over 3/4"! Even with a new boot, mine was a bit of a struggle to install, as if even the new boot is 1/4" too short.

I'm kinda surprised that you didn't paint the cylinder and head while they were off.

I think I spent about $30 for the flywheel holder. Believe me, it is well worth much more than $30. I shudder to think how much Yamaha charges for the "official" flywheel holder. 8O

The TW200, air box boot was unbelievably easy to install. This air box boot was undoubtedly the easiest, cheapest, and one of the best modifications I have made to my Zong!

I never considered painting either the cylinder or cylinder head, Weld. I prefer aluminum to paint; I'm waiting for the rest of my engine paint to fade away!

Spud

[SpudRider]

I rode 83 miles on the street immediately after I finished my engine rebuild. Therefore, I felt confident to ride my Zong to a local mountaintop today.







I'm pleased to report my Zong performed superbly! I really missed riding my Zong while I was waiting for parts to arrive so I could complete my engine rebuild. I'm very pleased to be back riding in the Zong's comfortable saddle!

Spud