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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
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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