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Pushrod deflection question.

Posted By: PUNK

Pushrod deflection question. - 05/18/10 01:44 AM

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.
Posted By: Cab_Burge

Re: Pushrod deflection question. - 05/18/10 01:51 AM

Mock one up with the pushrods in question using light springs, measured the lift at the retainers at +.100, +.200 and so on and then switch to the actual valve springs and measure them again slowly. See how much net loss there is If you can swith pushrods to a thicker wall or a bigger diameter with the same wall thickness and check them
Posted By: hemi-itis

Re: Pushrod deflection question. - 05/18/10 02:41 AM

Terry at Manton told me min of 10 thou.If deflection occurs,the heads will act like guide bars.
Posted By: polyspheric

Re: Pushrod deflection question. - 05/18/10 03:28 AM

No matter what a test shows, it's much more running.
Posted By: mr_340

Re: Pushrod deflection question. - 05/18/10 03:45 AM

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
Posted By: Thumperdart

Re: Pushrod deflection question. - 05/18/10 04:27 AM

Quote:

Terry at Manton told me min of 10 thou.If deflection occurs,the heads will act like guide bars.

That`s how it`s been working w/my rpm heads. I saw that they were close but figured that it was a built in guide bar of sort and so far after many street miles, passes and 5+ years it must be ok. Granted they were CLOSE but not touching as far as I can tell.
Posted By: gregsdart

Re: Pushrod deflection question. - 05/18/10 07:33 AM

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.
Posted By: 602heavy

Re: Pushrod deflection question. - 05/19/10 12:49 AM

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.

Posted By: MR_P_BODY

Re: Pushrod deflection question. - 05/19/10 01:07 AM

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

Posted By: 602heavy

Re: Pushrod deflection question. - 05/19/10 01:20 AM

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.
Posted By: vcummins

Re: Pushrod deflection question. - 05/19/10 12:40 PM

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
Posted By: PUNK

Re: Pushrod deflection question. - 05/19/10 11:51 PM

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.

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