Zongshen compression, low power
 

Hi
Past 5 days, my Zongshen sierra started to loose its power. The bike has over 25 000km, looks like its time for service.
I think it is loosing compression. Does anybody know what is normal compression value for 200cc (1:9,5) engine ? My manual doesnt say anything ??? Ive checked the compression, it is 125 psi ? is it low ?

Thanks

My Qingqi QM200GY (qlink XF200) with a CR of 9.4:1 has a permissible compression pressure of 139 to 199 psi. Yours with a slighly higher CR and only 125 psi seems below the limits.

Try repeating the compression test after putting a spoonful of oil down the plug hole. If it increases significantly it means the rings or bore are worn.
The oil forms a temporary seal around the rings and bore.

No change means valves are not seating correctly, either due to the clearances being too tight or burned valve seats.

Make sure the engine is warm and throttle is fully open while you carry out this test.

A quick figure for a reasonable compression figure for any engine can be calculated thus:

(CR x AP)+AP= compression pressure in PSI.

Where CR is the compression ratio
AP is normal atmospheric pressure (taken as 14.7 psi at sea level)

For yours this would be (9.5x14.7)+14.7= 154.35 PSI

Ok, i will do the test and report results.
Just few more questions,
1. Witch type of oil should i use in test (eg. fine mehanical oil or engine oil) ?
2. Why do i need to open fully trottle ? ( i didnt pull it in previous measuring compression, will it affect results) ?
3. Lets assume that ring and cylinder is warn, do i need to change them bouth ?

Thanks

1. Ordinary engine oil.
2. To allow the maximum amount of air into the cylinder. A closed throttle puts up a lot of resistance to air flow.
3. On inspection you may find the cylinder is OK and you can get away with just the rings. The cylinder will have to be inspected for scoring, etc and measured. You can get a quick idea of the state by just lifting the head and dropping the piston a little way down the bore. The top of the bore is not reached by the piston rings and will be the original diameter. if you feel with a fingernail and you don't detect a "ridge" or step, it's probably OK to re-use.

There is a problem with this. The bore, after a long service will be "glazed" and it'll have to be honed to bust that glaze and allow the new rings to break-in properly as well as renewing the oil-retaining surface finish of a new bore. Otherwise the rings will not bed-in properly and will never give you full compression.

A shop should be able to do a honing operation while you wait using their honing tool. There are several shade tree techniques though, but it's better to do it properly.

Re: Zongshen compression, low power
 

As usual, I think Forchetto has given you excellent advice. ;) My Zong has been running great, so I have neglected to check my engine compression. However, I do own a compression tester. As soon as I get the time, I will check my Zong's engine compression and post the results. Good luck, my friend. :)

Spud :)

Forchetto knows his SH%*, Good memeber to have here.

I like that expression... :D I think I'll quote it at my next works meeting :D :D

Max, I just checked the engine compression on my Zongshen Sierra 200GY-2. I followed the instructions posted at Dan’s Motorcycle Repair website.

http://www.dansmc.com/compression_test.htm

I followed Dan’s advice and tested the engine cold. However, I did forget to hold the throttle wide open. Also, I live at 4,400 feet above sea level. In addition, the temperature was about 45 degrees Fahrenheit. I tested the compression three times, and I got 105 psi from my Harbor Freight compression guage set.

http://i442.photobucket.com/albums/q...ketWear002.jpg

I am positive this compression gauge set is not the most accurate. Also, this gauge set has a very long hose, and an extra connection that might lose some air. :roll: Finally, I tested the engine cold, at 45 degrees Fahrenheit, at high elevation, with the throttle closed. However, it still seems to me that your reading of 125 psi is not too bad.

Later I will check the compression again, with the engine warm and the throttle open. However, I doubt I will gain much more than 20 psi when I do it. :?

My engine is running very well. Perhaps engine compression is not the cause of your problem. :?:

Spud :)

What's that green aligator clip for?

I attached the alligator clip to guarantee that the spark plug was grounded to the frame. It wasn't necessary; it was just an extra precaution. In fact, I fired up the starter with the engine cut-off switch in the "off" position. ;)

Spud :)

Hi
Thanks Spud for measurment.
Today i measured again compression, first i mesure compression on hot engine with trottle opened, it was 9~10 bar (130~145psi), then i putted small amount of 2T oil in cylnder, compression was very high 12,5 bar (180psi). For first few revolutions my kick starter was very hard, harder then it was before motorcycle stardet to loose power, is that normal ???
I started engine with oil in cylnder, i noticed that for first 3,4 sec. trottle has very high responde time, then again return to normal.
I dont know, is it compression or maybe carburator faulty ? becouse,my bike even it has loose his power is still working when i put it in neutral very nice and good.
Any help will be good, thanks
http://i226.photobucket.com/albums/d...n/P1080300.jpg
http://i226.photobucket.com/albums/d...n/P1080301.jpg
http://i226.photobucket.com/albums/d...n/P1080302.jpg

The second reading (180psi) is much more like it. The fact that the oil made such a difference that you could even feel it on the starter, points out to worn rings or cylinder. As I've said, the recommended limits on my Qingqi service manual are 139 to 199 psi.

Your compression tests certainly do seem to indicate either worn piston rings, or a worn bore, Max. I plan to recheck the compression of my warm engine tomorrow; I will post the results.

Spud :)

Hi all.
Well, i dissamble the cam head, looks like the valves was burned and warm, i changed new valves, cleaned the piston from carbon deposit, reasamble it and now its working fine :D :D , indeed better then before :D . Thanks everyone for helping me, specially spud, thanks :P

Max, I am very glad to hear that you found and repaired your problem! :D Ride safely, my friend. :)

Spud :)

Does this meaning the a-spoonful-of-oil trick doesn't work?

Shocked and stunned...the oil test should have confirmed worn bore and if it made no difference it would point to the valves. Still, all's well that ends well, glad you got it sorted.

I promise I didn't invent that procedure. It's in my gauge's users manual. I would have thought that after that mileage the rings would be a bit worn as well as the valves.

Just good that the problem is solved. Good for another 25K.

Allen

Amen on both counts, Allen! :D Max has got a tough little Zong! His 25,000 kilometers is equal to 15,500 miles; that's not too bad for a chinabike. ;) Today I just passed 10,000 miles on my Zong; it is still purring like a kitten. :D

Spud :)

Well, i think my compression gauge was faulty and not reading very well, every time when i was testing compression i got different values. So i dissable the engine, i putted some gas in cylinder and left it for 15minutes, not a single drop hasnt gone trough bore :D , so i assumed that valves was burned. I did the same test, putted valves in closed position, putted some gas in intake mainflood, wow :x , it just flood away in 5 sec, same thing for exhaust valve :evil: . I didnt want to refubrish valves becouse the new one are not so expensive, putted the new one, same test, not a single drop of gas :D .

But i think this engine faliure is my foult, becouse the last time iv checked valve clearrance was on about 8 000 km, becouse when i opened camhead there was no clearance between valves, so the valves didnt get back all way,and there was little micro-space between valves and head and the valves got burned slowly but noticable.

Great Spud, do not make mistake like me, check valves clearance every 6 000 km, good to know the bike is running strong :D

I should have 10,000 miles shortly. I rode today.

I was only planning for this bike to last 15,000 miles, but it runs great.

Allen

i have been fooled by the oil test myself here is my theory of why the valves the one i had was leaking and out of adjustment the oil will seal up valves just like it will for ring the test is still good just check the valves closely at the first sign of poor compression

Thank you for the good tip, Max. :) When you said the valves were damaged, I was tempted to ask if you had been checking your valve clearances. ;)

I adjusted my valve clearance two days ago. ;) This was the second valve adjustment I have done on my Zong, and the procedure went very fast; I was easily done in 30 minutes. :) After you do the procedure once, it becomes much easier the second time. ;)

I am very pleased to hear that your piston rings and bore are still in good shape after 15,500 miles. :) The 167FML engine in the Sierra 200GY-2 is a bulletproof little powerplant! :D

Based on your experience, and mine, I strongly encourage all motorcycle owners to read Red's superb Valve Adjustment Tutorial.

http://chinariders.net/modules.php?n...ewtopic&t=1655

If riders own a Zongshen 200GY-2, they also might enjoy seeing the photos I took during my first valve adjustment.

http://chinariders.net/modules.php?n...ewtopic&t=6458

Spud :)

I have purchase several parts bikes with broken valves from lack of adjustments.

Allen

I was thinking the same thing; the oil sealed the bad valves. ;)

Forchetto offered his usual, superb advice, which quickly diagnosed the compression problem. While checking the rings and bore, Max was easily able to discover the damaged valves. :)

You also offer excellent advice, Phil. If a bike owner has bad engine compression, he should always check the valves also, even if the piston rings are bad. ;)
Allen’s remark prompts me to make another observation. I think that chinabikes in general, and the Zongshen Sierra 200GY-2 in particular, have acquired a bad reputation for the wrong reasons. I believe that many new riders purchase these bikes used, and abused, from previous owners who did little or no maintenance on them. Then the new owners also neglect the motorcycles. I think they might do this for several reasons. First, they can’t get any local mechanics to work on them. Second, they are new riders, unfamiliar with motorcycle maintenance. Third, they do not value the Chinese motorcycle as much as a Japanese bike; they consider the chinabike to be a cheap, “throw-away” item. If they had spent a lot more money on a Japanese bike, they might have taken much better care of it. ;) Finally, after the motorcycle inevitably fails, they badmouth Chinese motorcycles as junk. ;) It is easier to blame the motorcycle than admit they did not maintain it properly.

Spud :)

I would like to add an update to my previous post in this thread. I recently tested the engine compression on my Zongshen Sierra 200GY-2 motorcycle. After making a valve adjustment, I measured engine compression with the throttle held wide open; I obtained a reading of 148 psi. This reading is much higher, and more reasonable, than the compression reading of 105 psi I reported in my previous post. :D

Spud :)