motor compression

albert · Post by **albert** » Fri Sep 05, 2008 6:19 pm

hy,,RAY,,i have 2 questions,, first,,, wend i take the motor compression,, i turn the key for to start the startor and make 3 up and down on the piston and on the guadge i read 135-150 pound of pressure ( on each piston ) ( witch 90 k mills on the original motor ) i thing that is correct but if i keep the startor ,,on,, for 5-6 up and down for the piston i have 185 on the scale for my compression ,, wy i have this reading ,,wy he d,t keep the 135 or 150 ,,, ( i take the compression test before and afther i adjust my valve ),,,,,wend the motor is cold,, oh my motor is 1.7 ,,d,,jet,, ,,, my second question is ,, i have gas pressure guadge ,, and i have instal my guadge on the gas line,,, T,,,,for the injector 3 -4 and that geeve me 28-30 pound of pressure on the idle spead or witch ,,2-3 k ,,rpm,,but afther i have stop the motor my guadge geeve me ,,0,, pressure afther 10-15 minutes ,, i thing the check valve afther the pump is fail,,, ( they name that fuel distributor in the book ) this thing is normal, or it is suppose to keep her pressure for 2-3 days ,, thanks for your help,,,albert

albert · Post by **albert** » Fri Sep 05, 2008 6:24 pm

oh,,RAY ,, i have test the injector for the leak of pressure afther the motor is stop and i d,t see any leak on the injectors ,

raygreenwood · Post by **raygreenwood** » Sat Sep 06, 2008 1:29 pm

Albert, it is possible that the check valve is bad, but usually it is more possible that the regulator is bad.
Try this....immediately after shutdown, crimp the return hose. If presure stays for quite a long time...then it is the regulator. If is still falls off in 15 minutes...its the check valve.

Its possible with your compression gauge that its check valve is doing someting strange. If you can find a compression gauge that has no check valve...a really old style one.....have someone else crank the engine while you watch....until the gauge quites rising in pressure. The maximum number it recahes will be your correct compression. Of course without a check valve it will bleed down alomost immediatley. But it will be accurate. Ray

albert · Post by **albert** » Sat Sep 06, 2008 2:28 pm

thanks ,,ray,, for this information ,, for my gas pressure check valve i doo your good test this week ,,but for my guadge compression my question was bad ,,, in the général vw book they said the compression is good if we have 120 to 150 ,p.s. for a motor 1.7 or 8.5 to 1 but now i have the 10w30 oil in the motor ( that can change witch the oil no 50 more clear ) but my maximum reading on the guadge is 180-185 afther 5-6 rpm for the piston but witch only 3-4 rpm for the piston i have 130-35 for all the 4 piston ,, samething for the maximum reading 180-85 ,on the 4 piston , my question was if my test witch 3-4 rpm was good or we waith for the maximum reading witch 5-6-7 rpm,, on the piston ,if i have now 175-180-185 on the maximum pressure witch the 10-30 oil what he geeve me witch the oil no.50 ( more clear ) he can drup onder the 120 no.??? i look for to do long ride in the usa ( 3k mi. ) nex spring witch my 412 and i know sometime you have very hight temp like 40 cel. or 90-95 fr. thanks,,albert