Pushrod shape

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Nefario
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Re: Pushrod shape

Post by Nefario » Tue Dec 12, 2017 7:22 pm

cgarb wrote:
Tue Dec 12, 2017 6:42 pm
Constrained pushrods has interested me also...
I’ve wondered how much column strength do you really need if the forces aren’t too great and it can’t go sideways? Piano wire? With a ball brazed on each end?

How about a really skinny pushrod with a short “twiddler rod” to follow the rocker arm? Valvetrain weight might be reduced considerably

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Re: Pushrod shape

Post by lefty o » Tue Dec 12, 2017 7:25 pm

Nefario wrote:
Tue Dec 12, 2017 7:22 pm
cgarb wrote:
Tue Dec 12, 2017 6:42 pm
Constrained pushrods has interested me also...
I’ve wondered how much column strength do you really need if the forces aren’t too great and it can’t go sideways? Piano wire? With a ball brazed on each end?

How about a really skinny pushrod with a short “twiddler rod” to follow the rocker arm? Valvetrain weight might be reduced considerably
another way to look at it is the larger diameter tubing used, the thinner the sidewall needs to be for the same level of stiffness.

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Re: Pushrod shape

Post by roc » Tue Dec 12, 2017 7:45 pm

I think Henry Ford, Rudolf Diesel, Clessie Cummins and alike were foolish in adopting round section pushrods. On the verge of being superseded by electric motors, square section pushrods are the next big thing for IC engines... fitted with triangular pistons #-o

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Re: Pushrod shape

Post by af2 » Tue Dec 12, 2017 8:27 pm

cgarb wrote:
Tue Dec 12, 2017 6:34 pm
I can tell you from experience with gun barrels, I know it is not the same as a pushrod...Some people claim that the fluting makes the barrel stiffer. It is not the same as a bead rolled into sheet metal. Any time you remove material from a barrel it gets weaker...I would have to say the same with pushrods. Only thing fluting would accomplish is to save weight.
Ha!! Along with wieght also to cool the barrel....More surface area..
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Re: Pushrod shape

Post by lefty o » Tue Dec 12, 2017 9:15 pm

cgarb wrote:
Tue Dec 12, 2017 6:34 pm
I can tell you from experience with gun barrels, I know it is not the same as a pushrod...Some people claim that the fluting makes the barrel stiffer. It is not the same as a bead rolled into sheet metal. Any time you remove material from a barrel it gets weaker...I would have to say the same with pushrods. Only thing fluting would accomplish is to save weight.
one of the engineers can come by and explain that fluted isnt stronger than solid of a same diameter, a larger diameter that has been fluted is stronger/more rigid than the same weight smaller diameter item. on a gun barrel they do to some degree speed cooling, but in a pushrod since their is oil on the inside and on the outside, i dont think it would make a bit of difference.

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Re: Pushrod shape

Post by engineguyBill » Tue Dec 12, 2017 9:53 pm

The concept of fluted pushrod could also be compared, to some extent, to the design of steel culverts used for roadway construction. The wavy (corregated) design of the pipe helps it to support much more weight than just a straight-walled pipe with similar material thickness would. A fluted pushrod may very possibly have similar strength characteristics as it's distant cousin, the corregated culvert . . . . .
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Re: Pushrod shape

Post by cgarb » Tue Dec 12, 2017 10:33 pm

Ah yes...the sewer pipe. The basis of all modern pushrod design.

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Re: Pushrod shape

Post by digger » Wed Dec 13, 2017 2:15 am

someone mentioned trees before, maybe they should add branches to pushrods

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Re: Pushrod shape

Post by digger » Wed Dec 13, 2017 2:28 am

lefty o wrote:
Tue Dec 12, 2017 9:15 pm
cgarb wrote:
Tue Dec 12, 2017 6:34 pm
I can tell you from experience with gun barrels, I know it is not the same as a pushrod...Some people claim that the fluting makes the barrel stiffer. It is not the same as a bead rolled into sheet metal. Any time you remove material from a barrel it gets weaker...I would have to say the same with pushrods. Only thing fluting would accomplish is to save weight.
one of the engineers can come by and explain that fluted isnt stronger than solid of a same diameter, a larger diameter that has been fluted is stronger/more rigid than the same weight smaller diameter item. on a gun barrel they do to some degree speed cooling, but in a pushrod since their is oil on the inside and on the outside, i dont think it would make a bit of difference.
firstly pushrods are mostly about stiffness not strength

the fluting does not increase the second moment of area any meaningful amount, and therefore offers no additional resistance to column buckling which is one of the main modes of failure of a long slender member under axial compression (notice i said axial and not radial some people dont appear to understand the difference based on recent posts)

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Re: Pushrod shape

Post by englertracing » Wed Dec 13, 2017 3:14 am

Well I've heard of the big push rod trend, in mountain motors I've heard the push rods described as telephone poles.

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Re: Pushrod shape

Post by BOOT » Thu Dec 14, 2017 1:49 am

Interesting comments, looked up some info and will more later. Is a tube a column? I thought columns were solid.
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Re: Pushrod shape

Post by BOOT » Thu Dec 14, 2017 1:59 am

Also rem the goal is to not deflect/bend, I wasn't able to find any real info on the force to start too bend either type tube and I'm not talking about surviving after it bends. Not that I looked a ton. Some of these examples don't really apply to a pushrod, the column would prob be the best other than they are solid I think. I posted this because I don't know(obviously) and didn't wanna put a lot of time into it and there are a ton of great minds on here but I haven't read anything to really convince me I'm wrong yet.
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Re: Pushrod shape

Post by digger » Thu Dec 14, 2017 2:41 am

a column does not need to be solid, it's basically a compression member oriented vertically

http://librarycivil.blogspot.com.au/201 ... lumns.html

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Re: Pushrod shape

Post by Sparksalot » Thu Dec 14, 2017 3:16 am

"Column" is engineering speak for a compression member with a relatively large L/D ratio or length divided by diameter. It doesn't mean the column is circular or solid it's just engineering speak again. We have means to calculate the strength of every cross section under compression under static or calm conditions. The failure mode we're trying to avoid is buckling, the classic bent pushrod.

Well known and fairly simple equations are available to determine what happens to a column under static conditions, a large part of it involves how the ends of the column are attached to their surrounding structure. A pushrod is minimally constrained at its ends for imparted bending effects, only by the friction of the ball and socket they all share whatever pushrod engine they come from.

Dynamically is another story. There are lateral accelerations on a pushrod too. It moves not in a straight line, there's a rocker sweeping it through an arc back and forth... Real shit happens.

Sorry! I launched into lecture mode. I hope to not do it again.

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Re: Pushrod shape

Post by Warp Speed » Thu Dec 14, 2017 5:15 am

Sparksalot wrote:
Thu Dec 14, 2017 3:16 am


Well known and fairly simple equations are available to determine what happens to a column under static conditions, a large part of it involves how the ends of the column are attached to their surrounding structure. A pushrod is minimally constrained at its ends for imparted bending effects, only by the friction of the ball and socket they all share whatever pushrod engine they come from.

This is exactly what many forget in their veiws on this subject!

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