Building my own SOHC Rocker Arms

[jayb]

I agree it would be interesting to do that analysis.  On the rocker shafts, I'm not aware of any tube that is available that meets my requirements.  Because the shafts are only going to be about .625" diameter, I need a very small hole down the middle to maximize the wall thickness of the shaft.  I've settled on 0.187" for the hole diameter, and can get it drilled locally.  If you or anyone else know of a source for tubing with .625" OD and .187" ID, please let me know.  It would save me the $30 bucks it costs to get each shaft drilled...

[Mario428]

  It would save me the $30 bucks it costs to get each shaft drilled...

$30.00 I laughed when I saw that, where I live has a long history of farming and fishing but no industrial activity, too remote. I only know of 1 gun drill and I would owe many favors to get some parts on it, $30.00 each would be a steal. LOL

[babybolt]

Jay, try this company:

http://www.teamtube.com/mechanical_tubing.htm

or

http://www.steelforge.com/alloysteels.htm

I just goggled HTSR 4140 tubing.

Somewhere it will be out there.

Since the SOHC rocker arm shafts are so well supported, strength isn't a super big issue.  If you really want to get trick, a DLC surface treatment will keep it from wearing out.

[jayb]

  It would save me the $30 bucks it costs to get each shaft drilled...

$30.00 I laughed when I saw that, where I live has a long history of farming and fishing but no industrial activity, too remote. I only know of 1 gun drill and I would owe many favors to get some parts on it, $30.00 each would be a steal. LOL

As luck would have it, there is a company fairly close to me called American Gun Drilling.  That's all they do, and they have a national client base, so obviously I'm getting the benefit of their volumes of work...

[jayb]

Jay, try this company:

http://www.teamtube.com/mechanical_tubing.htm

or

http://www.steelforge.com/alloysteels.htm

I just goggled HTSR 4140 tubing.

Somewhere it will be out there.

Since the SOHC rocker arm shafts are so well supported, strength isn't a super big issue.  If you really want to get trick, a DLC surface treatment will keep it from wearing out.

Thanks Doug, I will check those places out...

[WConley]

Let me know when you're ready to do an FEA 

[Cyclone Joe]

Hello Jay,

What strength/hardness are you attempting to achieve with the 4140?  Normally you order it to a specific hardness or strength range defined by the material specification.  If you know what your minimum strength values need to be, I can look up the spec and turn you to a couple of material suppliers.

Take care, and if you need material support on the rockers themselves dont be afraid to ask!

'Cyclone Joe' Burnett

[jayb]

Nice to see you here, Joe!  What I really wanted to use for a material was the same material T&D uses, which is 4130 steel heat treated to "Condition B".  I was unable to find that material in the size that I wanted, which is 1 1/2" square bar.  Several places on the internet listed it, but nobody could deliver it.  So, I ended up settling on 4140 because it was readily available from McMaster Carr; see the link to the material here:

http://www.mcmaster.com/#9116k413/=extteg

If I could find the 4130 Condition B material, I would definitely use that instead.  Know where I can get a 3 foot bar of that stuff?

[Mario428]

I did some tinkering with Cosmos in Solidworks and did some stress analysis on the rocker arm.

Using 4340 at 108,000 PSI and a 1000LB spring load (spring load itself and some acceleration forces = wild ass guess LOL)  the original design has some issues.
I did a rev B which took the rib, widened it to .19 from .13 and centered it on the roller at the valve stem, things look much better.

I am going to send you a couples of E-Drawing files you can take a look at Jay. If someone who knows a lot more about stresses than I do wants to take a look email me at mario.vanwiechen@marandeng.com, I will send the files and a link to a viewer for the files. Viewer allows spinning the 3-D model with the stresses shown

[jayb]

This thread is really starting to get engineering oriented, as I hoped it would; this is pretty cool stuff if you ask me LOL!  Both Mario and Bill Conley have done some analysis work on the rocker arm design.  This is FEA (Finite Element Analysis) stuff, and shows where you can get stress loading on the rocker arm.  Red on the analysis indicates high stress, and blue indicates low.  Mario felt that the rib on the rocker arm needed to be thicker based on the stress analysis, so he modified the rocker arm drawing to increase the thickness by .060".  Here are his two stress analysis results, with the original rocker design and the modified design with the thicker rib:





Bill did a dynamic analysis on the rocker, and sent me a couple of videos showing an exaggerated view of how the rocker deforms, at zero lift and also at peak lift, with a 1000 pound spring load.  Links to these videos are below:

http://fepower.net/Photos/Posts/BillC1.wmv

http://fepower.net/Photos/Posts/BillC2.wmv

Bill's comment was that the rocker design looked acceptable as is, especially given the use of the rocker.  Bill also thinks that the zero lift stress analysis is more important than the full lift analysis, because at zero lift the rocker arm has to start the valve and spring package moving, while at full lift the inertia of the valve and spring take some of the load off.  Bill's analysis showed a very slight twist in the roller end of the rocker when the load is applied, but nothing too substantial.  The deflection of the arm at 1000 pounds is 0.017", which is a little higher than the T&D arm (0.010"), but is probably the result of the smaller diameter rocker shaft, and the resulting smaller diameter of the body of the rocker arm.

It is interesting that the results of the FEA work is not quite the same, and points to differences between how the two analyses were set up.

In any case, either as is or with minor modifications it looks like the rocker will work out as intended.  I actually kind of like Mario's modification to make the rib thicker, because I'm going to have to drill a hole through that rib in order to oil the valve tip roller.  Making the rib thicker will make drilling or EDM-ing the hole easier.  That hole is also not part of the analysis, because it isn't drawn into the arm yet.  My plan on this was to wait until I had an aluminum rocker machined, test fit it on the head, and make any required adjustments to the design, and then worry about the oil holes.  So we will see how that works out...

[Cyclone Joe]

Hi Jay,

Here are a couple of sources I would suggest.  Tri-Tech Metals has ALWAYS found what I needed - from steel, titanium, niobium and everything in between.
http://www.tri-techmetals.com/  Ask for Sam.

I've also had good luck with these folks recently. 
http://rmat.com/

As for the material defined as 'condition B', this means that the material strength is a result of the 'as rolled' condition.  It will be stronger than annealed, but weaker than QT (quenched and tempered) N (normalized) or NT (normalized & tempered).  The as-rolled condition doesn't normally define a minimum yield or Ultimate strength (modulus remains unchanged however) or minimum hardness specifically.  I will look in MIL-HDBK-5 (the metal properties bible) and see if I can find any additional information.

You might ask T&D if they have a minimum hardness on their material as well as it being 'condition B'.  The hardness will allow us to calculate the yield and ultimate strength.  Otherwise, if you're open to it, I can suggest a couple of tempers that are easy to machine and would be stronger than the factory style rocker, and have a higher yield than 108 ksi.


Joe

[jayb]

Joe, thanks for the info.  I will try those sources.  Regarding the steel alloy itself, I picked 4140  pretty much because it was readily available.  I'm not stuck on the idea of using 4130 condition B, I just figured it would work well because that's what T&D is using.  Assuming I could get any alloy, which would you suggest?  I want to be able to machine it with minimal difficulty, and I don't want to go through any heat treat step after the machining process.  And of course I'd like to have the rocker arm as strong as possible.  Thanks - Jay

[Mario428]

Just to throw up a couple of pics of my own and get my $.02 in. GRIN


This view shows the displacement or flex that the rocker goes thru with a 1000 lb load. Note this is the Rev B rocker with a .190 rib centered on the valve end slot.
While it looks like it is twisted to hell LOL, note the scale shown on the pic and the number shown on the scale, scale is 28.7 to 1 and max displacement is 3.093e-001 mm or .012. Most of the displacement takes place around the hole and my beleif is the pin pressed in the hole will help support the hole.

Rev A rocker with .12 rib not centered on the slot

Scale is 19 to 1 for this one, displacement is 4.643e-001mm or .018
My concern would be the way the outside edge of the slot is twisted up

[cammerfe]

I have several thoughts.

First, it's obvious that we are now getting into the real cutting-edge of SOHC development. And, Jay, you're leading the charge.
Second, your stuff's so pretty you need to make some out of gold. They'd be just right nestled into the decolletage of a really first class blonde or redhead!
Third, wouldn't it make sense to look at EDM to create oil-holes.
Fourth, spacing 'donuts' along a piece of tubing and having them brazed into place in some 'alley' shop would seem to be a way of fabricating cam blanks. There're surely little shops here in the Detroit area that would be 'up' for such a job.

And all the above comments apply to those who're chiming in on this project. This is first-class stuff!!!

KS

[Mario428]

Had a flurry of emails with Jay & Bill late last week and my stress analysis was flawed.
Bill Conley has does a bunch of this kinda stuff and his model did a much better job of the analysis.
The decision was though to center the rib, will be interesting, looking forward to seeing one in metal.