Zongshen 200GY-2: Top End Rebuild at 31,656 Miles

[SpudRider]

After riding my Zong for 30,000 miles, I noticed several indications I might need to do a top end rebuild of my engine. I frequently ride my Zong into the beautiful, remote areas of Idaho. Therefore, I always strive to perform preventive maintenance, in order to avoid encountering engine problems far from civilization.

I thought it was time to perform a valve job, since my intake valve was not holding its adjustment. The intake valve clearance was consistently getting tighter, and I needed to adjust the valve lash every 500 miles. 8O Obviously, something was wearing down on the intake valve, and I want to avoid trashing my bike’s engine.

Also, although I had good compression, my engine had lost some power, and I was noticing the engine would stutter a bit while riding at wide-open throttle. My good friend Andy, a professional mechanic, suggested I should also do a ring job while I had the cylinder head removed from my engine. Andy also suggested I should rebore my Zongshen cylinder, and install an oversize piston with the new piston rings.

Since I had received over 30,000 miles of faithful service from my Zongshen engine, I decided to follow Andy’s advice. I ordered the necessary engine parts, and started to prepare for the job by reading the Yamaha, TW200 Service Manual.

Spud

[SpudRider]

My Christian brother Andy is a wonderful blessing in my life. Andy had previously acquired a Yamaha, XT200 engine, with a broken crankcase. Andy gave me the XT200 engine, and encouraged me to practice disassembling it while I waited for my engine parts to arrive. I wisely decided to follow his advice.

Using the Yamaha, TW200 service manual as a guide, I disassembled the XT200 engine. As I examined the XT200 cylinder head, I noted it was in excellent condition, and a perfect match for my Zongshen, 200GY-2 cylinder head! Therefore, I thought I might install the XT200 cylinder head, instead of rebuilding the Zongshen cylinder head. I showed the XT200 cylinder head to Andy, and a local motorcycle mechanic; they both agreed my plan was sound.

Since I had ordered an oversize, Yamaha, TW200 piston, along with oversize, Yamaha, TW200 piston rings, I made arrangements with a local machinist to rebore my Zongshen cylinder.

Since I need my daily dose of “throttle therapy,” I decided to wait until my engine parts arrived before I disassembled my Zongshen engine.

Spud

[mizke]

very nice, good luck with it and please take plenty of photo's.. its always fun to do internal work, and thats where you get the best performance from parts..

how big of a over size are you going ?

[SpudRider]

Originally Posted by mizke

very nice, good luck with it and please take plenty of photo's.. its always fun to do internal work, and thats where you get the best performance from parts..

how big of a over size are you going ?

Thank you, Mike. I am happy to say the job is completed, and I have ridden about 800 miles since. I installed a 2nd oversize piston, 0.50 mm larger than standard.

Spud

[SpudRider]

The engine parts arrived on a Wednesday afternoon, so I disassembled my Zongshen engine that evening. Upon removing the Zongshen cylinder head, I discovered why the intake valve would not hold its adjustment; the head of the intake valve was receding into the cylinder head. The photograph below shows my Zongshen cylinder head on the right, and the Yamaha, XT200 cylinder head on the left.



I had received almost 32,000 miles of very good service from this Zongshen engine. However, I am very glad I performed this top end rebuild before the intake valve receded farther, and possibly trashed my engine. I strongly encourage everyone to inspect his valve clearances on a regular basis. If your valves won’t hold adjustment, get the problem fixed before you damage your engine.

Spud

[SpudRider]

I had previously notified the local machinist when I would be disassembling my engine, and I made an appointment for him to rebore my cylinder. He told me he would complete the job the same day I delivered the cylinder to him! After calling the machinist to let him know I was coming, I removed the cylinder, and wrapped a towel around the connecting rod to keep debris out of the engine.



I had also decided to replace the camshaft chain, camshaft sprocket, and camshaft guides during this top end rebuild. Therefore, I removed both the left crankcase cover, and the magneto. To remove the magneto I used a Yamaha, TW200, magneto/flywheel puller, which is just a 16mm x 1.25 RH thread bolt.



I delivered the cylinder, and my oversize piston, to the machinist at 9:30 a.m. True to his word, he called me to pick up the rebored cylinder at 11:30 a.m.

Spud

[mizke]

good work man, bet it was fun.. the last time i had a motor apart it was installing cams in my autocross integra.. my friends where all for helping me pull the head and do the cam, valves, and dual valve springs but when it came time to put it all back together they got "busy" all of a sudden..

figure when my day comes for a rebuild. im going to pick up a trx 250r motor and do some custom motor mounts.. then market those motor mounts for people with gio beasts that want to run a honda motor.. can even begin to think how bad its going to be to try and find internals for my motor

[SpudRider]

After picking up the rebored cylinder, I returned home to complete the job. I installed one of the new camshaft chain guides, and the new camshaft chain. I then installed a new cylinder gasket, and a new O-ring around the oil passage leading to the cylinder head.



Spud

[mizke]

did you replace the stator when you pulled it ?

asking cuz im the type if i have to remove something might as well go ahead and replace it esp if its something that is a big deal to get to..


was this your first time diving into internal motor work ?
also hows the new found power or are you still into the break in of the new head..

[SpudRider]

I installed the piston rings according to the pattern described in the Yamaha, TW200 Service Manual. I then dipped the piston in motor oil before I installed the piston on the connecting rod, with the arrow facing the exhaust valve.

I oiled the cylinder. After pulling the camshaft chain through the cylinder, I lowered the cylinder onto the piston as I squeezed the piston rings with my fingers; the Yamaha/Zongshen cylinder has a nice bevel on the bottom, which facilitates this process.



Spud

[SpudRider]

After installing the cylinder head gasket, and another O-ring/gasket in the oil passage leading to the cylinder head, I installed the second, camshaft chain guide. I then pulled the camshaft chain through the cylinder head, and positioned the cylinder head in place.



I decided to use XT200 cylinder bolts, instead of the stock, Zongshen cylinder studs, to tighten the top end in place. I torqued the cylinder bolts to Yamaha specifications, then reinstalled the starter motor gear, and the magneto.

After installing the new camshaft sprocket, and setting the timing, I was ready to bolt the cylinder head to the engine frame.



Spud

[SpudRider]

After reinstalling the exhaust system, carburetor, fuel tank, et cetera, the job was completed. I have ridden about 800 miles since my top end rebuild, and I am very pleased with the results. In fact, my Zong is now running better than it did when it was new!

The Zong is a great little motorcycle, and I enjoy riding it very much. I am very happy I performed this preventive maintenance before I encountered any engine problems.

Spud

[SpudRider]

Originally Posted by mizke

did you replace the stator when you pulled it ?

asking cuz im the type if i have to remove something might as well go ahead and replace it esp if its something that is a big deal to get to..


was this your first time diving into internal motor work ?
also hows the new found power or are you still into the break in of the new head..

I had replaced the original stator at 10,500 miles, so I left it alone. I do have a spare stator in case I need it in the future. Fortunately, the Zongshen/TW200 stator is very easy to replace.

This was my first time doing a top end rebuild. I am very fortunate that my good friend, and Christian brother, Andy, is so gracious to answer my telephone calls whenever I encounter a problem!

The piston rings are still seating. However, I have noticed a significant increase in engine power. The Zong now accelerates much faster, and I have gained a 10 mph increase in top speed over the "old" engine.

My good friend Andy is a professional mechanic. After taking my motorcycle for a test ride, Andy remarked that my Zong "feels like a different bike."

Spud

[mizke]

very nice, you should buy your self a beer or soda if you dont drink.. tearing into a motor by your self even with phone calls as a safety net has a steep learning curve.. but you did good thumbs up..

again sorry for interrupting your postings, thought you were done cuz a few times it said you where logged off so i posted a reply, then saw you posted and it was more pics and stuff.. feel like that was pretty rude of me

[Weldangrind]

Good job Spud. It's remarkable how similar the XT and XR engines are internally. The cam chain setup is virtually the same. Did you decide to replace the valve stem seals on the head before installing it?

You're now at 199cc instead of 196. Also, an increase in bore also creates a small increase in compression as a by-product. Those two changes help account for the improvement in power.