Pushrod shape

[BOOT]

Very interesting topic.
I believe a square section 3/8", 0.060" wall thickness pushrod, would be stiffer than a round 3/8", 0.060" pushrod. But the square one will be noticeably heavier.....
Where the round section excels is it's ability to resist twisting compared to square or rect section. But this not an issue with pushrods so maybe the round shape is a good compromise between weight & strength, hence it's use.

Missed my point kinda, if it's stiffer why not use a smaller square that has comparable stiffness to the round, long as it's stiff enough to not break.

[BOOT]

Try going through engineering school if the original poster is serious about an accurate answer to the question. Yes, we know and there is absolutely no question about the right answer. His or her's were way off base.

I make no claims to be an expert in anything but if it makes you happy I have a degree in mechanical engineering. If you have details that explain what your saying plz share, I'm never afraid to change my mind or admit my idea was incorrect if the end result is better and I learn something.

[digger]

Try going through engineering school if the original poster is serious about an accurate answer to the question. Yes, we know and there is absolutely no question about the right answer. His or her's were way off base.

I make no claims to be an expert in anything but if it makes you happy I have a degree in mechanical engineering. If you have details that explain what your saying plz share, I'm never afraid to change my mind or admit my idea was incorrect if the end result is better and I learn something.

read two posts up

[engineguyBill]

Try going through engineering school if the original poster is serious about an accurate answer to the question. Yes, we know and there is absolutely no question about the right answer. His or her's were way off base.
[/quote

OK, I'll bite. WHAT is the correct answer??

[Warp Speed]

Round, double tapered pushrod is the strongest design - in my opinion. When was the last time you saw a square mast on a sailing ship? Or a square flagpole . . . . . . . ?

Wrong on the tapered vs straight pushrod. But let's not go there AGAIN! LOL

[Warp Speed]

Last time I checked, round tube has strength in all directions, square or rectangles maximum strength is directional.
Its all length vs cross section is it not?!?

[engineguyBill]

Yeah, that is why I added the qualifier "in my opinion . . . . ." It seems to also be the opinion of the major high performance pushrod manufacturers, though.

Carry on . . . . . .

[Warp Speed]

Yeah, that is why I added the qualifier "in my opinion . . . . ." It seems to also be the opinion of the major high performance pushrod manufacturers, though.

Carry on . . . . . .

The ONLY time a taper should be used, is for clearance purposes where a straight will not fit. Any manufacture that has the tapered is stronger opinion should be avoided!!!
Stiffness is all about length vs cross section..........period!

[englertracing]

square tube is not stronger than round as stated.
the idea of a fluted push rod is interesting, basically having external bracing makes it act like a much larger cross section, It may stiffen the push rod with minimal weight gain.

[Nefario]

I have a degree in mechanical engineering.

I do too. For a given cross-sectional area (ie mass) a round member is stiffer in unconstrained buckling than a square member because it has a greater moment of inertia (for that given area). Also you might look up "double butted" bicycle frame tubing which has thicker walls at the ends, sort of the same principle as a double tapered pushrod.

But - I've had some ideas for low-mass constrained pushrods I'd like to experiment with....square might be easier to deal with...

[cgarb]

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.

[cgarb]

Constrained pushrods has interested me also...If it was guided most of the way it wouldn't take much for a pushrod to work with high spring loads. Here's a thought...Have you ever seen the inside of a digital read out scale? A tube with a whole bunch of ball bearings inside. What if that same principle was used with pushrods. I know the whole part couldn't be ball bearings, the ends would need to be solid pieces capable of moving the duration of the valve lift without coming out of the tube or constraint. You could possibly make bent pushrods that would move out of the way of intake ports or whatever obstacle...Probably won't work, would be failure prone and put hundreds of ball bearings in the oil pan, but Its cool to think about stuff like that anyway...lol

[englertracing]

Constrained pushrods has interested me also...If it was guided most of the way it wouldn't take much for a pushrod to work with high spring loads. Here's a thought...Have you ever seen the inside of a digital read out scale? A tube with a whole bunch of ball bearings inside. What if that same principle was used with pushrods. I know the whole part couldn't be ball bearings, the ends would need to be solid pieces capable of moving the duration of the valve lift without coming out of the tube or constraint. You could possibly make bent pushrods that would move out of the way of intake ports or whatever obstacle...Probably won't work, would be failure prone and put hundreds of ball bearings in the oil pan, but Its cool to think about stuff like that anyway...lol

I think it's been done.

[englertracing]

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.

Regarding the fluting, for it to work you would have to go larger on the od then flute to get the weight back down for it to end up stiffer

[Nefario]

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