This seems to be a very unusual problem...at least to me. When I did my heads/ cam conversion a couple years back, I decided to change the lifters in the process. I used crane oe lifters which I thought would be sufficient for the size cam (cc305ish) and springs that were installed on the heads. Recently I've run across a problem that occurs at wot around 5200 rpms.The power drops off drastically which was verified during a dyno test. I've changed the valvesprings after finding 1 bad (85 psi seat pressure), added an inline pump since I still have the factory intank unit after 100k miles, and did a compression check which showed everything is fine. The strange thing is that one day while the motor was still cold, I decided to take off the valve covers and check the rocker adjustment. In trying to remove the cover, the end of it accidently hooked under one of the rockers and was able to swing it off the valve pretty easily. I had never seen this before so I attemted it on others and was able to do the same thing to some of them. Is this normal? Yesterday I decided to go through all of the rockers one more time but this time the motor was warm. They were all tight and would not budge from the head of the valve. A couple hours later when the motor had cooled down a bit, again I was able to swing some of the rockers pretty easily. Has anyone else experienced anything like this and if not would it be necessary for the to change the lifters again? Is there a stronger lifter I can try?

 

Probably find you get more responses on LT1 Tech..... moving it there.

 

I guess not

 

You've got a pretty crazy problem there. I'm having some valvetrain problems myself. I haven't tried what you did, but my car idles very rough and has low vacuum in the cold. When it warms up, it's fine. I'm suspecting bad lifters because this has been happening ever since I overreved and floated one (or more) of the valves. I don't know if this will help, TTT for you anyway.
Also, I'm looking for a good lifter recommendation if anyone has experience here.

JR

 

What you are describing isn't unusual at all. The hydraulic lifters are just bleeding off after sitting because of higher spring pressure. The only time that would affect the engine is when you first fire it after sitting a while. I bet it idles and revs rough as hell for the first ten seconds after sitting a few days. Well, mine is stock and does the same.

You didn't say what the spring pressure on the seat is. Also didn't say whether the car is running ok. Finally, do you not have guideplates? I haven't looked at LT1 heads lately but if guideplates can be added I would do so.

 

I'v used stock lifters w/306cam!! and had no problems,even at my 6500rpm redline,I would expect aftermarket parts such as crain lifters to be better then stock offerings.

 

Try these for the best results...