2006 ZS250GS

[FastDoc]

I don't want to sound too negative, this is simply what I did. :wink:

Parts for this bike are semi-available and inexpensive. It would be a bit of work to do the top end, but its not technically too hard. Indeed Spud has done his twice I think with great results.

Other options would be to transplant a 200-225cc Yamaha motor in there if you can find one. A 250 may fit also, I don't know. :?

It would be an unusual case of a Japanese motor transplanted into a Chinese bike, usually we do the reverse.

[katoranger]

It is fixable and yamaha parts have been confirmed to fit.

[Weldangrind]

I like the idea of digging into it, but it's not my time or money.

Just before you spin any wrenches, are you certain that you had the motor at TDC? If not, you won't accomplish anything. Apologies if you knew that already.

I like your new avatar. 8)

[SpudRider]

The bottom end of your engine is pure Yamaha. The camshaft, rocker arms, valves, and valve stem seals are most likely Yamaha parts as well. However, the cylinder, cylinder head, and associated gaskets are different, since Zongshen increased the cylinder bore to get the extra engine displacement above 196cc. If the oil test shows increased compression, you will need to order a Zongshen piston, Zongshen piston rings, and Zongshen gaskets.

Spud

[m0t0]

Well after several hours on Saturday i managed to yank the motor out of the chassis. Only today to go and do something stupid... (ill get to that part in a minute) I pulled the top off the motor, everything looked good. Except, the bolt that holds the top sprocket in place for the cam chain was halfway undone, and the threads halfway in were messed up. I was hoping that was all it was. Then i decided to take the piston off and just check it out. First clip came out fine and i was very careful. Second one not so much. As i was pulling it out i lost my grip on it for a split second, and am fairly sure in dropped inside. After several very colorful choice words, i decided the only thing to do was to tear the rest of the ******* thing down and find it. So as it stands now, i have it mostly torn down, working to separate the two halves. I'm hoping to get to the rest of it this week if not it will be next weekend.

In the mean time has anyone had any luck recently getting in touch with zongshen america? I have tried calling and emailing with no reply on either avenue. I would really like to get the gasket sets on order so i'm not waiting to put the damn thing back together.

Your very frustrated forum fellow
m0t0

[m0t0]

Originally Posted by Weldangrind

Just before you spin any wrenches, are you certain that you had the motor at TDC? If not, you won't accomplish anything. Apologies if you knew that already.

I like your new avatar. 8)

Weld,

A reminder never hurt anyone and i thank you for it I was as sure as i could be that it was at true dead center. I was able to wiggle the rocker arms so i was fairly sure.

P.S. Thanks on the avatar

[Weldangrind]

I've certainly had days like that; I hope the case splitting goes well for you.

I've only sent one email to Zong America, and there was no response. Kidd91 lives close to the warehouse and has visited them, and he says the address to use is Miamimoto305@hotmail.com . If you don't have luck with that email, perhaps Kidd91 would be willing to help you.

[m0t0]

Weld,

Thanks for the quick reply! I really appreciate it. I just fired an email off to that address in hopes that it offers better results than prior attempts. If not perhaps Kidd91 would be willing to be a third party. Will just have to see. :mrgreen:

[SpudRider]

Originally Posted by m0t0

Well after several hours on Saturday i managed to yank the motor out of the chassis. Only today to go and do something stupid... (ill get to that part in a minute) I pulled the top off the motor, everything looked good. Except, the bolt that holds the top sprocket in place for the cam chain was halfway undone, and the threads halfway in were messed up. I was hoping that was all it was. Then i decided to take the piston off and just check it out. First clip came out fine and i was very careful. Second one not so much. As i was pulling it out i lost my grip on it for a split second, and am fairly sure in dropped inside. After several very colorful choice words, i decided the only thing to do was to tear the rest of the ******* thing down and find it. So as it stands now, i have it mostly torn down, working to separate the two halves. I'm hoping to get to the rest of it this week if not it will be next weekend.

In the mean time has anyone had any luck recently getting in touch with zongshen america? I have tried calling and emailing with no reply on either avenue. I would really like to get the gasket sets on order so i'm not waiting to put the damn thing back together.

Your very frustrated forum fellow
m0t0

Please post a photograph of the upper cam sprocket and its bolt. I suspect your engine is very similar to the Zong/TW200 engine. If so, the cam sprocket is bolted directly to the camshaft itself. Also, the cam sprocket is kept from rotating by a small nub on the camshaft, but this nub only restrains the cam sprocket if the bolt is tight.

The gasket between both crankcase halves is a Yamaha gasket. However, because of the larger cylinder bore, you will need to get Zongshen gaskets for the cylinder base and cylinder head. The cam chain, camshaft, and cam sprocket are also Yamaha parts.

Spud

[katoranger]

Spud, is the cylinder different from a larger yamaha bore like the 225?

[SpudRider]

Originally Posted by katoranger

Spud, is the cylinder different from a larger yamaha bore like the 225?

Yes, Yamaha enlarged the bore and stroke of the XT225/TT-R225/TT-R230 cylinder to increase engine displacement from 196cc to 223cc. Zongshen enlarged the bore of the ZS250GS cylinder by 5.5mm to increase engine displacement from 196cc to 230cc. Therefore, the ZS250GS, 230cc cylinder sleeve is shorter, and larger in diameter than the Yamaha, 223cc cylinder sleeve.

Zonshen ZS250GS Engine Specifications: Bore 72.5mm, Stroke 55.7mm
Yamaha TW200 Engine Specifications: Bore 67.0mm, Stroke 55.7mm
Yamaha TT-R230 Engine Specifications: Bore 70.0mm, Stroke 58.0mm

Spud

[katoranger]

It appears that the xt250 has a 74mm bore and a 58mm stroke.

I wonder if there is any yamaha pistons that may fit.

[SpudRider]

Originally Posted by katoranger

It appears that the xt250 has a 74mm bore and a 58mm stroke.

I wonder if there is any yamaha pistons that may fit.

If the piston pin is the same size, one could have a machinist overbore the ZS250GS cylinder to 74mm. Then it would be possible to use XT250 pistons and piston rings. The bike would also gain a little more engine displacement.

Spud

[katoranger]

I don't know if the cylinder wall would be thick enough for that. I also think that the xt250 is a different case from the tw/xt200 so the cylinder probably wouldn't work.

[Weldangrind]

Originally Posted by katoranger

I don't know if the cylinder wall would be thick enough for that. I also think that the xt250 is a different case from the tw/xt200 so the cylinder probably wouldn't work.

I would agree. I think that the Zong ZS250GS cylinder would be required, and then the 200 Zong case would need to be bored to accept it. The extra 30cc would be a nice boost.