Little valve/lifter problem need some help on
Little valve/lifter problem need some help on Hey guys, need someone to check my thinking on a problem.. I installed a fairly mild cam and a set of mild (.04) heads, stock lifters, and 7.4in hardened pushrods. Tonight, I am installing a set of 1.7 yella terra rockers. I checked lash (all between .5 to 1 full turn of preload). Checking with an adjustable pushrod confirms the PR length. Wipe pattern looks excellent using no shims with the yella terras.
I noticed with both the stock rockers and the yella terras that when I set preload down to seat the rocker on the pedestal, it pushes the plunger in the lifter down a bit but then pushes open the valve slightly. I've tested 2 cylinders on each bank and confirmed the lifter was on the heal of the lobe. It's acting like it's bottoming out the lifter and pushing the valve open. I thought perhaps the lifter was still pumped up but when I started it with the yella terras it's got a slight miss and it's got a nice tick.
So the question is, even though everything checks out with wipe, lash, etc, why is it pushing the valve open just a bit? Is it the lifter is pumped up enough to hold the valve open? If that is the case, won't the valve sit just off the seat when the engine is running, also resulting in a loss of power and a tick? Trying to come up with next steps so any expert help is appreciated!
I noticed with both the stock rockers and the yella terras that when I set preload down to seat the rocker on the pedestal, it pushes the plunger in the lifter down a bit but then pushes open the valve slightly. I've tested 2 cylinders on each bank and confirmed the lifter was on the heal of the lobe. It's acting like it's bottoming out the lifter and pushing the valve open. I thought perhaps the lifter was still pumped up but when I started it with the yella terras it's got a slight miss and it's got a nice tick.
So the question is, even though everything checks out with wipe, lash, etc, why is it pushing the valve open just a bit? Is it the lifter is pumped up enough to hold the valve open? If that is the case, won't the valve sit just off the seat when the engine is running, also resulting in a loss of power and a tick? Trying to come up with next steps so any expert help is appreciated!
Make sure the valve closes when there is no PR installed. Make sure the rocker makes clean contact with the valve tip and not with the valve spring retainer or lock. But it seems as though the PRs are too long. Double check.
Set up the rockers (wipe pattern) and bolt them down, then use the PR length checker to find proper length. When you check for length, make sure the lifter's plunger is up all and that you are on the heel of the cam lobe.
Set up the rockers (wipe pattern) and bolt them down, then use the PR length checker to find proper length. When you check for length, make sure the lifter's plunger is up all and that you are on the heel of the cam lobe.
Last edited by ShevrolayZ28; Mar 20, 2008 at 12:03 PM.
I did all of the above including checking pushrod length. Ultimately, I went old school on it and set and checked wipe and pushrod length on each rocker on each cylinder. That I ended up with it is using various thicknesses of shims and switching over to to 7.35 pushrods. The published standard.. pick a cylinder on the power stroke, check pushrod length and implement results on all cylinders isn't the best way to do it and I think contributes to more sewing machine sound than anything. I'm going to post up what worked for me in another thread. But thanks for the help!
