vette427-sbc
08-07-2010, 07:01 PM
For a while I have been having trouble getting my valves adjusted right. A few months ago, I over revved my motor (~6500 RPM) and right after the over rev, I got a terrible valvetrain noise (sounded like a rocker came off). Limped the car home, and checked everything out. Adjusted the valves, and the noise went away, but the car never ran as strong afterwards. It would backfire on deceleration (only on the side that the valvetrain noise was coming from). I tried adjusting the valves again, but could never get the backfire to go away.
Possibly related, after this over rev, I began to notice that I would loose oil pressure at high RPM under load. Checked all the obvious for that- new HP HV oil pump, checked the pick up, no starvation, no oil burning, etc.. After attempting to adjust the valves one last time, I came to the conclusion that I could have collapsed a lifter, or it is bleeding out too fast.
Reasoning for this conclusion: When adjusting my valves, the lifter bleeds down and wont hold oil long enough to get a good lash adjustment, then pumps back up when I start the car, and doesnt let the valve close all the way. (This part might be a longshot)- High RPM's are making the lifter bleed out, which is causing my high RPM pressure drop as well. Also, oil pressure drop is a bit less prominent when the oil temps are still somewhat cold (thicker oil, harder to bleed out?).
This is all happening on the #7 cylinder (cant remember if it is exhaust or intake). I have a hydraulic roller cam with comp roller lifters that have the link bar. I adjust the valves by getting the car up to operating temp, shut it off, and find 0 lash by spinning the pushrod until it gets hard to spin by hand + 1/2 turn of the locking nut (all while the oil temps are still around 150*) I have had no problems doing it by this method before either.
Does any of this seem possible? Probable?
Edit: also did a leak down test on this cylinder with the rocker arms OFF. Everything turned out OK, so I can assume that the valve didnt kiss the piston and chip or break from the over rev
Possibly related, after this over rev, I began to notice that I would loose oil pressure at high RPM under load. Checked all the obvious for that- new HP HV oil pump, checked the pick up, no starvation, no oil burning, etc.. After attempting to adjust the valves one last time, I came to the conclusion that I could have collapsed a lifter, or it is bleeding out too fast.
Reasoning for this conclusion: When adjusting my valves, the lifter bleeds down and wont hold oil long enough to get a good lash adjustment, then pumps back up when I start the car, and doesnt let the valve close all the way. (This part might be a longshot)- High RPM's are making the lifter bleed out, which is causing my high RPM pressure drop as well. Also, oil pressure drop is a bit less prominent when the oil temps are still somewhat cold (thicker oil, harder to bleed out?).
This is all happening on the #7 cylinder (cant remember if it is exhaust or intake). I have a hydraulic roller cam with comp roller lifters that have the link bar. I adjust the valves by getting the car up to operating temp, shut it off, and find 0 lash by spinning the pushrod until it gets hard to spin by hand + 1/2 turn of the locking nut (all while the oil temps are still around 150*) I have had no problems doing it by this method before either.
Does any of this seem possible? Probable?
Edit: also did a leak down test on this cylinder with the rocker arms OFF. Everything turned out OK, so I can assume that the valve didnt kiss the piston and chip or break from the over rev