What are the effects of having too short of pushrods? - LS1TECH



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What are the effects of having too short of pushrods?

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Old 06-09-2010, 09:13 PM   #1
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Default What are the effects of having too short of pushrods?

I am about 99.9% sure that my pushrods are too short. I need to go from 7.4 to 7.45. What do you lose when they are too short? And before anyone makes a wisecrack, I'm not talking about my Johnson.
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Old 06-09-2010, 10:05 PM   #2
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As the block expands upward, the lifters may run out of being able to take up the lash.
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Old 06-09-2010, 10:13 PM   #3
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I think you will loose lift and be noisier. Your case is not too bad so I am not too sure but definitely you will loose a couple HP. Maybe someone with more expertise chimes in.
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Old 06-09-2010, 10:43 PM   #4
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- How were the pushrods measured?

- 0.05" shouldn't make too much difference... considering lots of people use 0.10" for their lifter preload.

- a quick check on a stock rocker setup would be to take your #1 cylinder to TDC and see if you can wiggle the pushrod up and down or wiggle the rocker back and forth. If there is any clearance then your pushrods are definitely too short...
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Old 06-09-2010, 10:49 PM   #5
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Pushrods that put the preload below the minimum of the range for the particular lifter can increase valve train noise and decrease oil pressure.
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Old 06-10-2010, 12:00 AM   #6
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its noramlly .050 for preload but if its like 0 or + anything with a hyd it will beat the parts to death over tiem
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Old 06-10-2010, 12:29 AM   #7
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Tap tap tap tap tap......
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Old 06-10-2010, 12:20 PM   #8
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im pondering the same question. i installed a cam with .010 smaller base circle, and milled my heads .010, so i figured if anything i would be .005 too short which shouldnt make much difference. when the car warms up the sewing machine noise becomes noticable around 2000rpm. It also doesnt seem to lope as much once its really warm, i thought that might be tunning but now that i think about it im wondering if my valves arent opening all the way when its warm?

i guess i really need to pull the valve covers off and measure my preload again to be sure, but this makes very good sense!
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Old 06-10-2010, 02:42 PM   #9
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noisier VT, decreased lifter life, possibly lower power, could be saving you PTV clearance if it was already tight.
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Old 06-10-2010, 09:15 PM   #10
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i'm sp new to this alot of what is being said is way over my head. What is lash? What is PTV? Excuse my ignorance but I'm learning. The rods were checked using an adjustable push rod. The method was to finger tighten the rocker down until there was no wiggle between the rocker and valve spring. Then mark the rocker bolt, tighten with a torque wrench to 22 ft/lbs and see how many turns it takes to get there. Optimum was supposed to be between 1-1/4 to 2-1/4 turns. It took adjusting the adjustable pushrod being 7.45 before I got there.
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Old 06-10-2010, 11:22 PM   #11
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what kind of rockers?
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Old 06-11-2010, 06:35 AM   #12
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Quote:
Originally Posted by LS-1Z28 View Post
what kind of rockers?
Stock rockers
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Old 06-11-2010, 08:54 AM   #13
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Quote:
Originally Posted by tg580 View Post
i'm sp new to this alot of what is being said is way over my head. What is lash? What is PTV? Excuse my ignorance but I'm learning. The rods were checked using an adjustable push rod. The method was to finger tighten the rocker down until there was no wiggle between the rocker and valve spring. Then mark the rocker bolt, tighten with a torque wrench to 22 ft/lbs and see how many turns it takes to get there. Optimum was supposed to be between 1-1/4 to 2-1/4 turns. It took adjusting the adjustable pushrod being 7.45 before I got there.
Lash is the clearance between mating components, so zero lash means that the push rod is just touching the rocker and neither is exerting any forces on each other.

PTV is piston to valve and is usually referenced as PTV clearance.
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Old 06-11-2010, 10:31 PM   #14
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bump!
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Old 06-12-2010, 10:48 AM   #15
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Quote:
Originally Posted by tg580 View Post
Stock rockers
you definitely want to measure it by adjusting an adjustable pushrod to zero clearance at the base circle of the cam (top dead center) and then add your preload (0.05-0.08). Also, The rocker should be torqued to 22 ft-lbs when you get your zero clearance measurement.
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Old 06-12-2010, 04:55 PM   #16
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Assuming someone install these incorrect figures....

.025-.050 too short = Incorrect valvetrain geometry, excessive amounts of noise, wrong preload, valvetrain instability that can cause power decreases and/or early power drop off

.050-.XXX too short = Stop, put your Stanley wrenches down, take them back to walmart, and pay someone else to work on your car.
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Old 06-15-2010, 10:41 AM   #17
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well i measured and im at about .037 pre load right now. i currently have 7.4's and i can get a great deal on some 7.45 in pushrods which would give me .087 preload, correct?
i see some guys on here running .100 and greater preload to quiet it down. what are your opinions on running .087"? and are my calculations correct?

Last edited by synisterC5; 06-15-2010 at 10:48 AM.
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Old 06-15-2010, 10:45 AM   #18
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well what do you have now?
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Old 06-15-2010, 10:47 AM   #19
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yeah im an idiot, sorry! i currently am running 7.4's
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Old 06-15-2010, 10:49 AM   #20
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Got your PM, 7.450's would put you at 0.087" preload from 7.400's
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cam, car, click, consequences, effect, incorrectly, installed, lose, making, noise, power, push, pushrod, pushrods, rods, short, sound

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