CHEV ASTRO knock/tap


#1

4.3L v6 Astro with 90K knocks/taps with engine speed in all gears. No oil/water loss. Fair compression - two outlyers 134 & 167 psi on the same side. Noise seems to come from high (just beneath valve cover)rear of engine on the opposite (good compression) side. Appreciate comments/and direction to search archives, so you all can stay on topic. Thanks

Swany Las Cruces, NM


#2

Sounds like a faulty hydraulic lifter. Another less possible cause could be a faulty pushrod. Sometimes the oil hole in the pushrod clogs up and the end of the pushrod can get beaten flat.

That 134 PSI of compression would concern me. That is way too low and means a problem exists. Squirt a spoonful of oil into that cylinder and recheck it. If the compression takes a big jump upwards then you have a piston ring problem. If it does not go up or goes up very little then there is a cylinder head valve problem.
90k miles is a bit young for a major problem, but…


#3

Thanks ok, yes 90K young in age too (2003). I don’t know for sure (too many kids/wife drivers), but I don’t think there has been a catastrophic oil or coolant event. I drive a 98 Bonneville, now in heavy demand while the (still paying for) Astro sits in the driveway. I changed oil (still have it), but did not find what I thought to be a problem. I replaced the spark plugs (broke a wire). The tip on the old #5 (157 psi) plug was bent way up and out away from the (core electrode?) gap area. Otherwise, the plugs look normal (original plugs). Roger that on the oil squirt, but that’s either bad or bad. If I need rings (might put it off) or valve job (can’t do myself), I will take my broke shit to the dealer and ask for mercy. I have a decent view through the spark plug hole. The valve cover is fairly accessible. Where do I go next…