proper compression for 50cc and info on Bintelli head and cy
by: scooter - Jul 5, 2015 18:36:49 GMT -5
Post by scooter on Jul 5, 2015 18:36:49 GMT -5
I am getting cold compression readings on a 139QMB of only 90psi.
Another test showed 70 psi and then, after oil was put into the cylinder, about 120 psi.
Please tell me, what is the standard psi for these engines?
One source online said about 15-20 times the compression ration of 10.5:1 or about 158 - 210 psi. Several youtube videos showed 50cc compression at around 160 or so, on up to 190 with a cold engine.
One source said a MINIMUM of 100psi if it's to be considered usable at all, and another said 120 MINIMUM, but a healthy engine seems to push much higher, well over 150.
I am pretty sure 90psi is crap, but I want a standard number to compare it to when I tell my client what's going on with the bike. I'd also feel better with a standard number in hand before I start taking the top end apart.
I think we had once discussed that a good start would be 14.696 psi times the stated compression ratio of 10.5, which would be 154 psi. 70 would only be 45% of that, and
would still only be 58% of 154.
ALSO
This is a Bintelli Sprint 50cc with EGR. Does anyone know if this takes the standard cheap-chinese-ebay heads and cylinders for 139QMB's? I also need to address the 64mm vs 69 mm valve length question.
This one has 69mm valves, confirmed by measurements. There are videos on youtube that show you how to tell the difference just by looking at the base of the springs and the height of the valve retainers above the top edge of the head.
Another test showed 70 psi and then, after oil was put into the cylinder, about 120 psi.
Please tell me, what is the standard psi for these engines?
One source online said about 15-20 times the compression ration of 10.5:1 or about 158 - 210 psi. Several youtube videos showed 50cc compression at around 160 or so, on up to 190 with a cold engine.
One source said a MINIMUM of 100psi if it's to be considered usable at all, and another said 120 MINIMUM, but a healthy engine seems to push much higher, well over 150.
I am pretty sure 90psi is crap, but I want a standard number to compare it to when I tell my client what's going on with the bike. I'd also feel better with a standard number in hand before I start taking the top end apart.
I think we had once discussed that a good start would be 14.696 psi times the stated compression ratio of 10.5, which would be 154 psi. 70 would only be 45% of that, and
would still only be 58% of 154.ALSO
This is a Bintelli Sprint 50cc with EGR. Does anyone know if this takes the standard cheap-chinese-ebay heads and cylinders for 139QMB's? I also need to address the 64mm vs 69 mm valve length question.
This one has 69mm valves, confirmed by measurements. There are videos on youtube that show you how to tell the difference just by looking at the base of the springs and the height of the valve retainers above the top edge of the head.
