Zongshen compression, low power

[max_damage]

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

[forchetto]

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

[max_damage]

Originally Posted by forchetto

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

[forchetto]

Originally Posted by max_damage

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.

[SpudRider]

Originally Posted by max_damage

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

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

[AZ200cc]

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

[forchetto]

Originally Posted by AZ200cc

Forchetto knows his SH%*

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

[SpudRider]

Originally Posted by max_damage

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

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.



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

[Dragon]

What's that green aligator clip for?

[SpudRider]

Originally Posted by Dragon

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

[max_damage]

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

[forchetto]

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.

[SpudRider]

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

[max_damage]

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 , indeed better then before . Thanks everyone for helping me, specially spud, thanks :P

[SpudRider]

Originally Posted by max_damage

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 , indeed better then before . Thanks everyone for helping me, specially spud, thanks :P

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

Spud