Commando Pushrod Tech

Time for a new tech thread. A couple years ago I bought some basic tooling from Comp Cams for making pushrods, and have been making custom length Commando pushrods to order. I've so far made them in 2024 T3 aluminum tube, in either .058" wall or .090" wall. Stock Commando pusrods are .062" wall tube, and the .058" wall ones I make come out pretty close to the same weight as the originals. The .090" wall tubes are heavier but also sturdier, but I'm not sure that's an advantage. I'd like to do some dyno runs of the .058" wall pushrods against .090" wall pushrods in an engine with a radical cam, but probably won't ever manage it. Peter Williams is a big fan of using steel pushrods, as is Steve Maney. They seem to feel that the extra weight is more than made up for by the increased stiffness. I'm thinking of setting up to also do steel pushrods. Pretty much all the pushrod automotive engines use heavy wall steel pushrods, so maybe that says something too. Titanium is also a possibility, but I seem to recall some issues with using it for pushrods. I'll have to try to hunt that down, unless someone here can enlighten me.

So here's my question. Do any of the tech experts here care to weigh in on the pros and cons of different material choices? Any experience here?

I'm pretty sure the best choice would be the aluminum/ceramic MMC tubes that 3M has, but Smith Brothers tried and gave up on making them. I taked to them about it a while back, and they said the rods worked fine on the Harleys they built them for, but the cost of production was just too high for the limited market size. They have to be machined with diamond tooling, and they had problems with the small diamond reamers breaking, adding lots of expense. The material isn't real cheap either. When I talked to 3M they were only supplying it in pre-cut 12" lengths, so you would waste a lot of material making Commando length pushrods.

This is what the pushrods in .058" wall tubing look like. The ends are from Smith Brothers.



and for the other gearheads, this is the tooling from Comp Cams.





Ken

What are the weights of the steel, and the two AL pushrods?

For comparison, the values I measured on one sample of the longer (intake) pushrods are the following:

Stock Commando pushrod - 29.7 g
My .058" wall pushrod - 29.5 g
My .090" wall pushrod - 40 g

I have not yet made any pushrods in 4130 steel, so I can't give you a weight, but probably somewhere around 50 g, similar to the Alloy-Tech ones listed below.

I also measured some other Commando intake pushrods I had laying around, just for info. These are no longer manufactured.

Alloy-Tech aluminum pushrod with steel ends - 29.8 g
Alloy-Tech aluminum pushrod with hard anodized aluminum ends (not a good idea, wore through the anodizing) - 22.7 g
Alloy-Tech 4130 steel pushrod with steel ends - 50g
Carbon fiber pushrod with steel ends - 28.3 g

Steve Maney lists his steel pushrods as lighter than stock, so he must be using thinner wall tubing. I have not tried that because I don't have a source of the ends in the right size. Steve had to make his own ends to fit the thinner wall tube.

Ken

A little more info. When I started this, I made some engineering calculations to see what wall thickness was required to get the same column bending stiffness in pushrod tubes of different materials.  I looked at steel, aluminum, and titanium.  I used .049" wall 2024 aluminum as a baseline, and calculated the wall thickness required in 4130 steel and in grade 9 titanium to get the same stiffness.  Then I calculated the pushrod weights with those wall thicknesses.  For the same stiffness, the aluminum and titanium rods were the same weight, and the steel rod was a lot heavier.  You wouldn't gain anything from using titanium, and it would be a lot more expensive.  You might also have trouble getting tube in the right wall thickness.  You'd need titanium with .027" wall thickness, and the closest size I could find is .035".  If you used that, the rod would be heavier.  With steel, you'd need .025" wall, and the closest I could find is .035", so it's even heavier.  All in all, it looked to me like aluminum was the best material.  The bending stiffness of thin columns is primarily a function of the modulus of elasticity, not the tensile strength.  Aluminum is also better at shock absorbtion and vibration damping than steel or titanium, and I think that should also be considered.  It might be that there are other considerations.  Peter Williams preferred steel pushrods, and that's what Steve Maney uses, so I could be missing something.  I'd have to dig into some technical papers on the design of pushrods to see if that's the case, and I haven't done that. That's why I'm trying to pick the brains of folks here on the list.

Ken

Hot rodders have long found that the mass of the push rod doesn't make much difference to rpm and response but most definitely any added stiffness does.
Peel will need a custom push rod fit, got a set of Maney'd already paid for along with cases/barrel/primary, still waiting to tell him what length to ship.

"If you all would just spend a day on the Spin-tron, there would be no question. You would all be running the stiffest pushrod you could fit in the engine, and you would care nothing about the added weight."

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Interesting stuff about tapered pushrods, but it was my understanding for using them was that the different diameter of the tapered pushrod results in different frequenciy distribution that the pushrod will oscillate at. Also, the shorter length of each individual tapered area results in the frequency band moving higher up the spectrum, as compared to one long length untapered pushrod.

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More of this in here
http://www.chevelles.com/forums/archive ... 23499.html

mass producing these parts is fascinating to watch here.
[video]http://www.youtube.com/watch?v=eHwcG8tPJbA[/video]

hobot said:

Hot rodders have long found that the mass of the push rod doesn't make much difference to rpm .

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That is not a good statement to blanket over the subject. The mass of a pushrod and lifter was found by Smokey Yunick to not make any difference in the rpm valve float took place at, but it was in an application where the rocker-arm ratio was at least 1.5:1, which is definitely not what the Norton twin is.

Are the custom pushrods being tried as large in diameter as they can be? That certainly adds stiffness to a "column" right? The pushrods are very close together and that would limit diameter, but what if they were made very large diameter with one flat surface on each facing each other just like the lifters, out of paper thin tubing, with a strip of teflon on one of them to keep them from rotating. Then you could have a very large dimension in at least one....dimension...

With all the work and tinkering in this area trying to get somewhere, I am always amazed that no one grind a full relief cam that is the full diameter of the stock cam tunnel, the ends "coning" down to the bearing diameter for maximum stiffness in the application. With stock rockers modified to 1.3:1 ratio the lobe lift would only have to be .250", greatly decreasing the inertia of the stock lifter and pushrod, so then like Hobot said, their mass would not matter. The cam lobes for this rocker ratio could be far less aggressive for the same valve action, and in fact would allow valve action that a Norton twin has not yet seen.....

Also with a full relief cam that from a side-view looks like a circle, it would be far easier to buy a proprietary needle-roller bearing that would simply slip over it and rest against the existing cam tunnel.....held in place by a simple spring-steel strap and screw.

Drill holes in the top of the rocker box and put the rocker adjusters on the pushrod side of the rocker, with a handle on a long-reach socket for the locknut and a tee-handle allen wrench for the set-screw rocker-ball/stud, then you can grind half a large bearing roller to a half-circle, silver-solder it to the valve-end of the pushrod and have a line-contact rocker with less mass on that end than the stock setup. With titanium valves and the much lighter springs that would be needed, now the valve train can finally be forgotten.

I guess that just about does it......

I'm not an engineer but JS motorsports mention the difference of expansion between aluminum and steel push rod tubes as the are heated up, and that stands to reason, but with a cast iron barrel and aluminum head and cases????? Maybe it's related only if you have anuminum cylinders. Cj

lcrken said:

I bought some basic tooling from Comp Cams for making pushrods, and have been making custom length Commando pushrods to order.

Ken

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Ken is on top of this and it sounds like he is offering a unique service - tell everyone your prices.

beng that's was super interesting valve train read to hop on and contort my mind to follow. Should be straight forward if tedious modifications, can't wait to see and hear it working out like crazy. Someday after Peel more matured, may have you talk a machinist into doing this. Once valve train bullet proof, what next limits rpms, besides long friction stroke?

Definitely a thermal expansion issue to compensate for while measuring and building cold.

cjandme said:

I'm not an engineer but JS motorsports mention the difference of expansion between aluminum and steel push rod tubes as the are heated up, and that stands to reason, but with a cast iron barrel and aluminum head and cases????? Maybe it's related only if you have anuminum cylinders. Cj

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My 1960 ES2 has alloy head and barrels, and by the book the valves are set with zero clearance. Push rods free to spin but not able to be rattled.

beng said:

Are the custom pushrods being tried as large in diameter as they can be? That certainly adds stiffness to a "column" right? The pushrods are very close together and that would limit diameter, but what if they were made very large diameter with one flat surface on each facing each other just like the lifters, out of paper thin tubing, with a strip of teflon on one of them to keep them from rotating. Then you could have a very large dimension in at least one....dimension...

Click to expand...

I'm using 3/8" tubing, same as stock Commando. Larger would be nice, bu I don't think there's enough room in the pushrod tunnel at the head-to-cylinder interface for anything much larger in the front-to-back direction, especially in the larger bore engines. I think it's also necessary to allow the pushrods to rotate to reduce wear at the balls and cups on the ends. Interesting ideas, though.

Ken

Hi Ken

Great post.
I just use standard alloy pushrods with the cups shaped (reduced a bit)
I do remember a couple of years ago someone running carbon fibre pushrods.
I agree it is an area to look at, so all the best in your search.
We have a little 350 MV twin that revs well. Easy to over rev. The tunnels are bigger than the Commando but the push rods shave themselves to an amazing degree. You cant believe that they can bend like that! Same solution they are replaced with steel ones.

Chris

At a tech evening (organised by Jan Wolfert NOC nederland )a man told us he looked at std pushrods in an std engine with a strobe and afterwards he never used std pushrods in a racing engine again , so much were they flexing
i believed him and always used maney ones , about same weight and much stiffer as std ones .As the pushrods were flexing they compromised camtiming(jumping off lobes etc ) and put undue load on the valve train

oh yes , the bloke's name was Peter Williams

Chris said:

I do remember a couple of years ago someone running carbon fibre pushrods.

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My friend, Martin Adams, tried carbon fiber pushrods in the engine in his Commonwealth Norton back in the '80s. As I recall, one of them shattered into tiny bits, so he went back to aluminum. I think I still have the other three pushrods.

Ken

I suspect that carbon fiber has to be engineered for the purpose - compression without flex. Isn't most carbon fiber tube stock designed to flex, e.g., fishing rods and golf club shafts?

Reminds me of a St. Croix fishing rod brochure wherein I read about their rods that incorporate a glue made by 3M that is infused with nano particles that bolster or buttress the carbon fibres - sort of like gravel in cement to make concrete.

Thanks for all the good inputs everyone. It does seem like steel pushrods are probably the best of the readily available solutions. My problem with them is finding available ends for thin wall 4130 tube. Neither Smith Brothers or Comp Cams, the two places I've found that sell the ends, have them with a large enough shank to fit the 4130 tube. I've explored having batches of ends made by a local job shop, but it doesn't seem to make economic sense, given the limited market for them. I'll keep looking for options, but for the moment, I think I'm sticking to aluminum, and maybe some steel ones with .058" wall for my own use, even if they are a bit heavy. Using the radiused BSA lifters saves a good bit of weight at that end of the valve train, so maybe it will all balance out. Then again, I can always just have Steve Maney make his lightweight steel ones in whatever length I need. Trouble is, I just like making my own stuff.

I have found some interesting references on the subject, that I'll try to hunt down and read. There are a bunch of interesting articles about valve train design, including one on pushrods, available on the Blair web site,

http://www.profblairandassociates.com/RET_Articles.html

Ken

lcrken said:

Thanks for all the good inputs everyone. It does seem like steel pushrods are probably the best of the readily available solutions. My problem with them is finding available ends for thin wall 4130 tube. Neither Smith Brothers or Comp Cams, the two places I've found that sell the ends, have them with a large enough shank to fit the 4130 tube. I've explored having batches of ends made by a local job shop, but it doesn't seem to make economic sense, given the limited market for them. I'll keep looking for options, but for the moment, I think I'm sticking to aluminum, and maybe some steel ones with .058" wall for my own use, even if they are a bit heavy. Using the radiused BSA lifters saves a good bit of weight at that end of the valve train, so maybe it will all balance out. Then again, I can always just have Steve Maney make his lightweight steel ones in whatever length I need. Trouble is, I just like making my own stuff.

I have found some interesting references on the subject, that I'll try to hunt down and read. There are a bunch of interesting articles about valve train design, including one on pushrods, available on the Blair web site,

http://www.profblairandassociates.com/RET_Articles.html

Ken

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Can you shrink the ends of the steel tubes some how? maybe in a press with tapered holes, or roll them?

Cheesy said:

Can you shrink the ends of the steel tubes some how? maybe in a press with tapered holes, or roll them?

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I'm sure there's a way to do that, but it does add another process, and it would leave the ends, which are .375" diameter, hanging out over the smaller tube diameter. I think a more likely approach would be to have the ends machined by the job shop, but do the hardening myself. A good bit of the cost quote I got was for hardening them after machining. I might pull out the drawings and get some quotes.

Ken

Ken,
My old racebike had holes in the top of the head for pushrod access. I was running a 560n480 cam and switched to Maney steel pushrods from stock aluminum pushrods in the search for more power. It made zero difference in the dyno reading.

Steel pushrods with aluminum barrels limit your camshaft selection to those built for large clearances. If you run steel pushrods and an aluminum barrel with a cam designed for .008 or less clearance you would set them at zero clearance cold but when the engine gets hot the clearances will increase so much that the quieting ramps will no longer be used. The valve train will then wear more rapidly. [particularly the seats]

My preference is steel for steel barrels and aluminum with aluminum barrels. Both with cda990 bronze ends. Jim