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

 

half way down the page is an good explaination. When one valve is compressed Like say the intake I adjust that cylinders exhaust. So I do multi valves with each rotation. Time is money. I am 100% against the running motor adjustment.

At work I use a magnetic base dial indicator to set the lash on HR motors to the .020 plunger depth

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if you're spinning all the pushrods they must be straight.

I bet you're not adjusting the valves correctly. I push the pushrod up and down unitl it just moves a very slight amount. Then go 1/4 turn.

6500 is really not that bad an ovrerrev.

look at all the rocker studs. are they the same height.? you may have one pulling out.

 

I dont use a dial indicator to set the plunger depth, but I do adjust each valve when the other is being compressed. (ie: The exhaust valve begins to open, I adjust the intake. And as the intake is just beginning to close, I adjust the exhaust)

Yes, I forgot to mention I checked all of the pushrods and they are good and straight. I am 100% sure I am adjusting the valves correctly. I have done it many times with no problems, it is the same cylinder (#7) that gives me problems every time. I have AFR heads with screw in studs. None are pulling out. Comp says it is possible to get valve float as early as 6200 RPM with the steeper ramps of a hydraulic roller. I could have pushed it further than 6500 too- I wasnt really looking. Shift light wasnt hooked up and I dont have a rev limiter.

 

I would check the spring pressures as that is the problem with over reving a motor. Once a spring has been pushed to its limit, it looses tension then it lowers it rev potential and each time You get close to that limit it drops more. Thats where I would start looking, assuming everything else checks out like You have said.

 

I really dont get on it much any more with the engine running like this... maybe 4k RPM at the autocross last weekend but I cant remember the last time I brought it out past 5000 RPM. I think the backfire that Im getting on deceleration is because one of the valves isnt closing all the way. A weak spring would still let it close, but it would just float earlier than the rest, right?

More info: I put on some valve covers with the tops cut off and let the car idle for a minute... No weird valvetrain noises and all the rockers seemed to be moving the same amount.

Thanks everyone for the ideas so far

 

If the spring is weak it won't close properly. It can actually bounce off the seat. Using roller lifters can make it even worse with the weight of the valve train. The spring is the only component that causes the valve to close.

 

I just noticed Your mention of the valve cover cut outs. I don't know if this will work or not but try this. Take a piece of wood and hold it over the valve on the rocker and push down with the engine off and the valvles in the closed position. You may be able to feel the weaker spring if there is one. It would be interesting to try that while it was running but You run the risk of bending valves.

 

I had a comp hyd flat tappet in my big block and over reved it and collapsed 1 lifter. Motor had about 1000 miles on it. Have also read on some other forums of people having problems w/ the hyd rollers from comp too. Not saying this is your problem, just something to look at. Good luck, hope it's nothing bad

 

I ordered a new (pair) of lifters today... Hope to get it running this weekend. I hope this fixes the rough running problem, and Ill be ecstatic if it happens to cure my oil pressure problem too. Ill keep you all updated, Thanks