Pushrod deflection question.
#700879
05/17/10 09:44 PM
05/17/10 09:44 PM
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Joined: Dec 2004
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Rancho Cucamonga, Calif.
PUNK
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I understand that there are many variable that dictate how much a pushrod will deflect such as overall length, width, wall thickness, valve spring pressure, valve train component weight, RPM of the engine, heat treatment, and construction material of the pushrod; but is there a general number to use for factoring actual valve lift when teh engine is operating? I know its complicated to say based on so many variables, but is it safe to say that a pushrod will deflect .020" regardless of all these variables? .030", .040". Lets say a 3/8 pushrod with a .080" wall thickness with an overall length of 7.75". Would it be safe to say at 650 pounds of open spring pressure that the pushrod will deflect a minimum of .020??....Or what as a minimum. Im not asking for absolutes, basically what as a minimum could be expected.
10.53 @ 125mph. 1.37 60 foot. Caltracs and Monoleafs, AFCO shocks.
Heads by INDIO MOTOR MACHINE; IMM.
CP Pistons, PC Carbs.
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Re: Pushrod deflection question.
[Re: PUNK]
#700882
05/17/10 11:28 PM
05/17/10 11:28 PM
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Joined: Oct 2007
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New York
polyspheric
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master
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New York
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No matter what a test shows, it's much more running.
Boffin Emeritus
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Re: Pushrod deflection question.
[Re: PUNK]
#700883
05/17/10 11:45 PM
05/17/10 11:45 PM
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DFW
mr_340
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Quote:
I understand that there are many variable that dictate how much a pushrod will deflect such as overall length, width, wall thickness, valve spring pressure, valve train component weight, RPM of the engine, heat treatment, and construction material of the pushrod; but is there a general number to use for factoring actual valve lift when teh engine is operating? I know its complicated to say based on so many variables, but is it safe to say that a pushrod will deflect .020" regardless of all these variables? .030", .040". Lets say a 3/8 pushrod with a .080" wall thickness with an overall length of 7.75". Would it be safe to say at 650 pounds of open spring pressure that the pushrod will deflect a minimum of .020??....Or what as a minimum. Im not asking for absolutes, basically what as a minimum could be expected.
http://www.engineersedge.com/column_buckling/column_ideal.htm
No difference on the heat treatment. Almost all steels have the same modulus or within a few percent. The equation listed is not the exact equation because it's pinned, but still will give you an idea of the important parameters.
http://en.wikipedia.org/wiki/Buckling
Floyd Lippencott IV
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Re: Pushrod deflection question.
[Re: Thumperdart]
#700885
05/18/10 03:33 AM
05/18/10 03:33 AM
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Frostbitefalls MN (Rocky&Bullw...
gregsdart
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I am going off memory, but thought I observed .020 to .022 loss with the old 3/8 heavy wall pushrods from Indy, new 1/2 inch tool steel lost .010. Both tests were with 340 lbs on the seat.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Pushrod deflection question.
[Re: 602heavy]
#700887
05/18/10 09:07 PM
05/18/10 09:07 PM
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Romeo MI
MR_P_BODY
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Quote:
3/8 .080" wall pushrods with 650lb spring pressure will possibly deflect a heck of a lot more than .020" , will look like bananas when you pull em out  , @ least shoot for .145" wall if using 3/8th.
I've never seen any where near that... I use a 3/8
tapered to 5/16 .080 wall moly 7.2 long PR and I
have about .035 clearance to the PR with 800# at
lift... never seen any marks on the PR or the head...
maybe I'm just lucky
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Re: Pushrod deflection question.
[Re: MR_P_BODY]
#700888
05/18/10 09:20 PM
05/18/10 09:20 PM
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Joined: Dec 2008
Posts: 1,200
UK
602heavy
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Quote:
Quote:
3/8 .080" wall pushrods with 650lb spring pressure will possibly deflect a heck of a lot more than .020" , will look like bananas when you pull em out , @ least shoot for .145" wall if using 3/8th.
I've never seen any where near that... I use a 3/8
tapered to 5/16 .080 wall moly 7.2 long PR and I
have about .035 clearance to the PR with 800# at
lift... never seen any marks on the PR or the head...
maybe I'm just lucky
Just my  , although i was refering to 9 3/4 long PR.
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Re: Pushrod deflection question.
[Re: PUNK]
#700889
05/19/10 08:40 AM
05/19/10 08:40 AM
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Joined: Oct 2005
Posts: 294
mi
vcummins
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mi
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Quote:
I understand that there are many variable that dictate how much a pushrod will deflect such as overall length, width, wall thickness, valve spring pressure, valve train component weight, RPM of the engine, heat treatment, and construction material of the pushrod; but is there a general number to use for factoring actual valve lift when teh engine is operating? I know its complicated to say based on so many variables, but is it safe to say that a pushrod will deflect .020" regardless of all these variables? .030", .040". Lets say a 3/8 pushrod with a .080" wall thickness with an overall length of 7.75". Would it be safe to say at 650 pounds of open spring pressure that the pushrod will deflect a minimum of .020??....Or what as a minimum. Im not asking for absolutes, basically what as a minimum could be expected.
Lot depends on the cam ramp. roller with 260-280 @ 50 with 650 over the nose your on seat is around 260-270. You don't want to use the block or head for A guide. If you can run 3/8 rods that's A plus and make them .120 wall. with the new cam profiles you need wall thickness to keep the p rod from acting like A leaf spring storing energy and unloading on the closing side of the lobe and bouncing the lifter off the cam at the base. I have been there
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Re: Pushrod deflection question.
[Re: 602heavy]
#700890
05/19/10 07:51 PM
05/19/10 07:51 PM
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Joined: Dec 2004
Posts: 1,717
Rancho Cucamonga, Calif.
PUNK
OP
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OP
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Quote:
3/8 .080" wall pushrods with 650lb spring pressure will possibly deflect a heck of a lot more than .020" , will look like bananas when you pull em out , @ least shoot for .145" wall if using 3/8th.
I was just using a standard 3/8 pushrod as an example. The ones im using in the new engine are Manton Series 5, 3/8, .145 wall straight pushrods. Thanks for all the responses guys. Just trying to figure out what may be a good number to use as a pushrod deflection number to figure the actual lift at the valve. There are more variables, but this is one that Ive heard many different sides of the story on.
10.53 @ 125mph. 1.37 60 foot. Caltracs and Monoleafs, AFCO shocks.
Heads by INDIO MOTOR MACHINE; IMM.
CP Pistons, PC Carbs.
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If you can swith pushrods to a thicker wall or a bigger diameter with the same wall thickness and check them
