PRC 265 & LS7S Cam install near completion - strange valve issue when checking PR
05-05-2013, 10:06 PM
#1
Teching In
Thread Starter
Join Date: Dec 2011
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
PRC 265 & LS7S Cam install near completion - strange valve issue when checking PR So I'm seeing the light at the end of the tunnel with my first head/cam install. I'm doing PRC 265, LS7S cam (242/250 .650/.650 @1.8 rocker, not sure what the base circle measurement is)
I just installed the heads and torqued both of them down and am at the checking pushrod length stage.
First I checked number 1 cylinder both intake and exhaust, then moved over to the number two cylinder. Everything is checking out between 10.5 and 10.75 turns of my comp cams checker.
I move over the the number 6 cylinder and this is where it got weird. I installed the checker at 10.5 turns, and well the follower was not on the base circle. So i snugged the rocker down, and turned the engine clockwise until i heard and saw the valve close. gave it a few more degrees to be sure it was on base circle and checked the play in the rocker. Ok so it has just a little bit, I can still hear it "tick", so I pull it off, and turn it to 10.75 turns. Now as I put it back on, i see the valve move down a little bit. What the heck? So i turn the crank again and watch it compress fully and then close back up, hear and see it close. Now I check the play again and it's just about right. I just loosen the rocker bolt a couple turns and the rocker tip comes loose as soon as the bolt breaks. The valve doesn't move it all. It is def on base circle. Now just to see, i put the bolt back in a couple turns and the valve moves down again.
What can be causing the valve to move down when the follower is on base circle?
After I tightened the bolt down snug, the valve was slightly depressed. So I turn the crank over, watch it cycle and now it's back on base circle, and I loosen it just a couple turns, valve doesn't move. Tighten it back and the valve moves down just a little.
This happened on both the intake and exhaust on the #6 cylinder, but didn't happen at all on the #1 and #2.
Second thing is when i installed the #1 stock pushrods and rockers, just so i could turn the motor over a couple times for a safety check to make sure the timing was right and no interference. Everything was fine and turned over smoothly, but on each valve spring, just as it passed the point of being fully compressed and moving into rebound, it made a slight "tick" noise, not from the spring, it sounded like from inside the engine, like on the cam I did this several times and on both the intake and exhaust valve, when the spring compressed fully and passed into rebound I heard the faint "tick". This also happened on the other cylinders I was messing with to determine PR length.
The third thing I want to ask about is the PR length itself. Has anyone installed this combo of cam/head (UNMILLED, GM GASKET) and found the pushrod length to be this long? I started with a Comp Cam Checker 7901-1 (7.5" - 8.7"). At 10.5 turns, i could still hear "tick tick" when checking play in rocker. At 10.75 turns it was just a bit of play no tick. at 11 no play at all. Katech is recommending .075 preload for the stock LS7 lifter. So (10.5x.05)+7.5+.075 = 8.1 pushrods. Am i doing this right? I will have to go with that length since I dont' see anyone selling a (10.75x.05)+7.5+.075 = 8.1125 pushrod
I just installed the heads and torqued both of them down and am at the checking pushrod length stage.
First I checked number 1 cylinder both intake and exhaust, then moved over to the number two cylinder. Everything is checking out between 10.5 and 10.75 turns of my comp cams checker.
I move over the the number 6 cylinder and this is where it got weird. I installed the checker at 10.5 turns, and well the follower was not on the base circle. So i snugged the rocker down, and turned the engine clockwise until i heard and saw the valve close. gave it a few more degrees to be sure it was on base circle and checked the play in the rocker. Ok so it has just a little bit, I can still hear it "tick", so I pull it off, and turn it to 10.75 turns. Now as I put it back on, i see the valve move down a little bit. What the heck? So i turn the crank again and watch it compress fully and then close back up, hear and see it close. Now I check the play again and it's just about right. I just loosen the rocker bolt a couple turns and the rocker tip comes loose as soon as the bolt breaks. The valve doesn't move it all. It is def on base circle. Now just to see, i put the bolt back in a couple turns and the valve moves down again.
What can be causing the valve to move down when the follower is on base circle?
After I tightened the bolt down snug, the valve was slightly depressed. So I turn the crank over, watch it cycle and now it's back on base circle, and I loosen it just a couple turns, valve doesn't move. Tighten it back and the valve moves down just a little.
This happened on both the intake and exhaust on the #6 cylinder, but didn't happen at all on the #1 and #2.
Second thing is when i installed the #1 stock pushrods and rockers, just so i could turn the motor over a couple times for a safety check to make sure the timing was right and no interference. Everything was fine and turned over smoothly, but on each valve spring, just as it passed the point of being fully compressed and moving into rebound, it made a slight "tick" noise, not from the spring, it sounded like from inside the engine, like on the cam I did this several times and on both the intake and exhaust valve, when the spring compressed fully and passed into rebound I heard the faint "tick". This also happened on the other cylinders I was messing with to determine PR length.
The third thing I want to ask about is the PR length itself. Has anyone installed this combo of cam/head (UNMILLED, GM GASKET) and found the pushrod length to be this long? I started with a Comp Cam Checker 7901-1 (7.5" - 8.7"). At 10.5 turns, i could still hear "tick tick" when checking play in rocker. At 10.75 turns it was just a bit of play no tick. at 11 no play at all. Katech is recommending .075 preload for the stock LS7 lifter. So (10.5x.05)+7.5+.075 = 8.1 pushrods. Am i doing this right? I will have to go with that length since I dont' see anyone selling a (10.75x.05)+7.5+.075 = 8.1125 pushrod
05-06-2013, 09:47 AM
#2
Teching In
Thread Starter
Join Date: Dec 2011
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
After a little more reading i realize i was activating the lifter plunger when checking this. So you are supposed to check this rocker play without pushing down on the lifter plunger?
I did bathe the lifters in oil for 24 hours but now that they are installed they are probably draining? So the plunger is easier to activate?
I did bathe the lifters in oil for 24 hours but now that they are installed they are probably draining? So the plunger is easier to activate?
05-07-2013, 03:14 PM
#3
What I have found to be the easiest way, and works good, is to get a set of 8" calipers and measure the pushrod after getting it set to 0 lash. Just add how much you want to compress the lifter and order the pushrods that length. It's much easier than trying to count turns.
05-07-2013, 06:08 PM
#4
What I have found to be the easiest way, and works good, is to get a set of 8" calipers and measure the pushrod after getting it set to 0 lash. Just add how much you want to compress the lifter and order the pushrods that length. It's much easier than trying to count turns.
06-26-2013, 08:12 AM
#5
Teching In
Thread Starter
Join Date: Dec 2011
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
I found out that the Magnum PR checker from Comp Cams is not designed to measure by turns anyway. It is intended to measure absolute length (like with 8" calipers).
I was confused because measuring absolute length with actual pushrods will not give you the functional length due to the ball ends and oil hole. For instance, the stock LS7 PR measures 8.021 when it is functionally an 8" rod.
I was confused because measuring absolute length with actual pushrods will not give you the functional length due to the ball ends and oil hole. For instance, the stock LS7 PR measures 8.021 when it is functionally an 8" rod.
