I'm an idiot.

[FastDoc]

The Zong's got poor compression. I should have checked that first before dumping $200 in parts and a lot of time into it.

I can easily hold my thumb over the spark plug hole while cranking the motor. Adding some oil to the cylinder did not help so I think it's the valves. They are adjusted so that's not it either.

I have $400 into it. Anyone wany a $200 project bike? Maybe Spud can get you a new motor inexpensively and you'd have a like new bike.

As for me, I'm done with it.

[Weldangrind]

If you send me the head, I can try replacing the valves for you. Alternatively, maybe you can find a Yamaha head that fits, like Spud did.

[FastDoc]

Thanks, buddy but I think I'm gonna cash out. I'd rather not put more time into the bike, although it may be a simple bad valve and fixable very cheap. My heart's not into it, I won't turn a profit on it, so I'd just as soon let it go.

oh that sucks man, I shouldv thought of that ! whenever I was working on my RM250 or my TZR250 I uselly always check the compression !!! it actually makes perfect sense with all the symptoms you had on your bike !
Anyway I'll see if anyone around here wants it. Good luck with the sell !

[Reveeen]

Of course you realize: that a head gasket, blown between the cylinders (or the timing chain cavity), would cause the problem you describe?

Ok, I know, too easy, right? (nothing EVER works out that easy for me)

For the want of a $6 gasket it's worth a look!

[Weldangrind]

My thoughts exactly.

And a buch of China Rider enablers will needle you until you take it apart. :lol:

[katoranger]

Just do it. No cost involved in a top end tear down. Do it for the sake of future information for others. :lol: Call it research.

Also check into the yamaha sr250.

[Weldangrind]

And take pictures. Lotsa pictures. :lol:

[SpudRider]

Just do it. No cost involved in a top end tear down. Do it for the sake of future information for others. :lol: Call it research.

Also check into the yamaha sr250.
X2! As with your "Dirt Rat" restoration, you have broken new ground with the Zongshen 250GS project, Doc! If you have space in your garage, I strongly encourage to stick with this project a little longer. ;) All of us have enjoyed watching your work on this project, and we have learned a lot from you. :)

Spud :)

[FastDoc]

Another update.

I (tried to) pull the head. The valves look OK but there are vertical scoring marks on the cylinder so I think that's the problem. I was unable to pull the head all the way off. It does not seem possible with the motor still in the frame.

I'm not sure I want to hone and re-ring or install an oversize piston. I'm still inclined to part it out.

What's a motor for one of these cost, Spud? Are oversize pistons available?

[FastDoc]

It came to me this AM how to remove the head with the motor in the frame. Will decide what to do based on Spud's avalibility of parts.

[katoranger]

It may be possible to use yamaha parts. Let us know if it appears to has a broken ring or what went wrong.

Allen

[FastDoc]

I looked at it again. No way to get the head off without pulling the motor and the swingarm/rear suspension. :evil: The head looks identical to the Yamaha. I don't know what's wrong. the cylinder is very lightly scored but otherwise it and the valves look OK.

[Weldangrind]

Does it have a decompression device like a Honda? Maybe that's hanging open.

You could always hook up an airline to the spark plug hole and see where the air goes. That'll tell you where the horsepower is leaking.

[Cal25]

Any chance of a valve stuck partially open?

[Weldangrind]

Maybe it has a broken ring, which would certainly account for compression loss.

For the unfamiliar, if you connect an air hose to the spark plug hole, you can find where the compression is leaking. Slowly rotate the engine until it becomes obvious; air flowing out of the exhaust is a bad exhaust valve, air flowing through the carb (with the carb open) is a bad intake valve, and air flowing out of the crankcase breather tube is a bad ring.

You can either buy the adapter that screws into the plug hole or make your own. I made one by breaking the ceramic out of an old plug, removing the insulator and ground electrode and tapping the inside of the metal body to accept an air quick-connect fitting.

[Barnone]

W&G,
A broken ring makes sense since FastDoc says the cylinder wall is scored.

That is a nice looking bike that deserves to be repaired.

[katoranger]

I am leaning toward ring too. Slight chance of a wrist pin coming loose.


Doc. Need some pics.

[FastDoc]

I'll see about pulling the motor, but like I say I'd rather just get rid of it. I have a lot of time and some money into it at this point. Since one of our Washington members is interested in it, and I may be out in his area to look at a KLX, I'm inclined to put it back together and on the trailer.

[recracer]

don't feel bad about not checking compression first Doc . heck i am a mechanic and bought a 85 gl1200 goldwing in need of repair . so i charged it up and gave it a crank and it was running on the right bank only. right off the bat thought ,bet it's the left bank timing belt ,this being an 85 with 18,000 miles . i pulled the radiator and fairings to get there . belts were intact after all that . i pulled the 2 left spark plugs both fouled . felt a little like homer simpson at that moment , i resolve it needed belts anyway :oops:

[kmoore]

bought a 85 gl1200 goldwing in need of repair

not trying to thread jack but if you need parts i have an 86 gl1200 im parting out pm me if you need anything

now back to the original topic

[mizke]

doc, you could prolly find a company that sells a complete top end.. awhile back i came across a yamaha warrior that had a something jacked up and on its way out in the top end. did some research and found a company that sells complete ready to bolt on top ends for a wide range of motors. the warrior top end kit was less then 200 with shipping..

id vote to fix it and then sell it if you wanted to.. you could net a good amount more cash in the end with the bike not only running, but having a brand new top end.

[FastDoc]

I've never heard of anyone breaking a Gold Wing in less than 100,000 miles! What did the prior owner do to that poor bike? 8O

I have someone coming over tomorrow to look at the Zong. :?

I look at it like this. If the bike could not last 3,000 miles without puking some major component I don't want to put more time into a poor machine. Plus, what else is wrong? Maybe it was a lubrication issue and the camshaft is galled? The mainbearings? What if I make it run and discover the clutch is shot and that's what killed the motor?

This particular Zong is not in the same category as Spud's excellent motorcycle.

On this forum, Mychinamoto, and on the Zong forum these GS250's seem to give nothing but trouble.

[humanbeing]

...On this forum, Mychinamoto, and on the Zong forum these GS250's seem to give nothing but trouble.
There's a common doggerel about ZS in Chinese: "è´ä¹°å®—ç”³ï¼ŒåŽæ‚”ç» ˆç”Ÿ" :oops: