Pushrods too long? Valves hanging open
Pushrods too long? Valves hanging open So I installed new Brian Tooley .660" Dual springs, retainers, seats, seals and locks on my PRC stage 2.5 LS6 heads on my 403 LQ4 tonight and when I went to re-install the pushrods and tighten down the stock rocker arms I noticed something weird.
When I tighten down the rocker arm with the cam on the base circle (valve should be closed) the rocker pushes open the valve about a 1/4". I verified that the valve was actually opening by looking down the intake runner and watching the valve open. I made sure that the cam was on the base circle by bumping the engine over until the valve closed, then I loosened the rocker arm and the valve would close even more. Is it possible that the pushrods are too long? They are 7.400" TSP pushrods. I'm curious because I didnt notice this problem with the old valve springs. Any help is appreciated.
When I tighten down the rocker arm with the cam on the base circle (valve should be closed) the rocker pushes open the valve about a 1/4". I verified that the valve was actually opening by looking down the intake runner and watching the valve open. I made sure that the cam was on the base circle by bumping the engine over until the valve closed, then I loosened the rocker arm and the valve would close even more. Is it possible that the pushrods are too long? They are 7.400" TSP pushrods. I'm curious because I didnt notice this problem with the old valve springs. Any help is appreciated.
Did you give them some time to bleed down? You will normally see the valve open a bit when installing the rocker but it will slowly close afterwards. I found this when using a dial indicator for measuring lifter preload. The needle would settle for several minutes. Although 1/4" seems like a lot.
Last edited by vettenuts; Oct 24, 2013 at 04:04 AM.
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From: Turnin' Wrenches Infractions: 005
Sounds like I would be double checking the measurement. If in fact they are hanging open, then you are virtually building no compression. You can tell this 1 by turning the motor over by hand (it will be very easy) and 2 the starter spinning the motor will wizz away like something's broke (no compression to fight against). It should be plainly obvious whether the engine has compression. And, the above is correct, the valve will often tip open when first tightening everything down but it should not stay open.
Ok, I got this figured out. Not sure exactly what was causing it most likely it was lack of bleeding off lol Anyways I moved on to tighten the rest of the rocker arms and some of them did this and some didnt. So I went back to the first one that I was having problems with and loosened it and re tightened it and it didnt do it again. Learn something new everyday. Thanks for the help gents!!!
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Verdad Gallardo I get 0.084" of preload with that number of turns. Not sure I would change pushrods at this point other than larger OD.
Grab a pencil and hold one end of it. Now grab the middle of the pencil and lower it as if you were tightening a bolt on a rocker. You will see that as you drop the center of the pencil that the outer end you are not holding will drop far more than the center point or (bolt) does.
The .050 preload per 1 turn is an internet myth that won't go away because people refuse to measure properly.
1.375 turns - 0.333 turns from rocker bottom to 22 lb-ft = 1.042 turns of rocker motion (note, this is based on my measurements).
1.042 turns X 1.25 mm/turn = 1.3025 mm
1.3025 mm/25.4 mm per inch = 0.0513 inches of rocker movement
Correct for rocker ratio, stock rocker with valve closed ratio is 1.54
0.0513 * 2.54/1.54 = 0.0845" of preload.
You need to account for rocker bolt preload and the rocker ratio:
1.375 turns - 0.333 turns from rocker bottom to 22 lb-ft = 1.042 turns of rocker motion (note, this is based on my measurements).
1.042 turns X 1.25 mm/turn = 1.3025 mm
1.3025 mm/25.4 mm per inch = 0.0513 inches of rocker movement
Correct for rocker ratio, stock rocker with valve closed ratio is 1.54
0.0513 * 2.54/1.54 = 0.0845" of preload.
1.375 turns - 0.333 turns from rocker bottom to 22 lb-ft = 1.042 turns of rocker motion (note, this is based on my measurements).
1.042 turns X 1.25 mm/turn = 1.3025 mm
1.3025 mm/25.4 mm per inch = 0.0513 inches of rocker movement
Correct for rocker ratio, stock rocker with valve closed ratio is 1.54
0.0513 * 2.54/1.54 = 0.0845" of preload.
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