Rocker arms with non-roller tips

[SchmidtMotorWorks]

I am making a set of 4340 steel rocker arms for a friends SBC that runs about 10,000 rpm. He is hoping that a rocker of the same weight as the current aluminum rockers might last longer, I guess it is possible but I wonder why there aren't many steel rockers used in drag racing. The only ones I can think of are the billet ones from Brad Anderson and the investment cast ones from Stage V.

I'm willing to go along with the experiment but I wonder what to do about the valve-end, roller or solid?

I think I remember reading somewhere that the small radius on roller tip rockers wears the valves or lash caps more than a rocker that is solid but larger contact radius.

Does anyone have experience with solid tipped rockers with high valve spring pressure?

I am thinking of using materials and heat treatment similar to billet crankshafts.

[SchmidtMotorWorks]

I found this image of a rocker used in NASCAR, no roller or adjuster, I guess they have a variety of lash cap thicknesses. Anyone know how rockers like this perform?

[shawn]

That's a really interesting idea. I have often wondered how much frictional loss there really is at the tip of the rocker. I would think that with some of the amazing coating products out there that a coated lash cap and coated rocker tip (as long as it will take the impact) would work just fine. I've seen some roller rocker tips with "flat spots" on them, indicating that the pressure against the roller is not allowing it to roll anyway. Here's a link to the Schubeck rocker that doesn't use a typical roller tip either.

http://www.schubeckracing.com/new2/inde ... tion=70:53

shawn

[OldSStroker]

I am making a set of 4340 steel rocker arms for a friends SBC that runs about 10,000 rpm. He is hoping that a rocker of the same weight as the current aluminum rockers might last longer, I guess it is possible but I wonder why there aren't many steel rockers used in drag racing. The only ones I can think of are the billet ones from Brad Anderson and the investment cast ones from Stage V.

I'm willing to go along with the experiment but I wonder what to do about the valve-end, roller or solid?

I think I remember reading somewhere that the small radius on roller tip rockers wears the valves or lash caps more than a rocker that is solid but larger contact radius.

Does anyone have experience with solid tipped rockers with high valve spring pressure?

I am thinking of using materials and heat treatment similar to billet crankshafts.

How about looking at Comp Cams Pro Mags which are 8650, a higher carbon Ni-Cr-Mo steel than 4340. Note they have less mass at the valve than aluminum rockers.

http://www.compcams.com/Technical/Curre ... ML/311.asp

or Hi-Tech Stainless, which are 15-5 Precipitation Hardening Stainless.

http://www.compcams.com/Technical/Curre ... ML/313.asp

Reinventing the wheel is fun, but doing the development to make it work is long and costly.

Now, for 10K, you might be looking at shaft-mounts, right? If you don't like the stuff from Jesel, etc. consider the steel grades Comp uses if you must build lyour own. Buy a Pro-mag and reverse engineer it for heat treatment. It'll save you a lot.

I can't picture purposely using non-rollers for that kind of rpm. All those side loads mentioned by Ken0069 put a lot of bending loads on the valve, so you need strong (read that as heavy) valve stems.

Assuming rules didn't prohibit it, for 10K I'd consider skinny stem (8mm or even 7 mm) Ti intakes and hollow SS exhausts and springs that use small diameter retainers. Obviously reducing the mass of the moving valve train parts, including the springs, reduces the spring pressure required, and the loads on everything including the rockers. Mass is the enemy here.

My $.02

[SchmidtMotorWorks]

Comp Cams Pro Mags

That's an investment casting, in my experience you give away about 40% in strength with a casting compared to machining from bar stock.

I'm planning on something much lighter than the Comp part, more like the image I posted.

[SchmidtMotorWorks]

Anyone knwo a good source to buy

adjusters
locking nuts
tip rollers and pins
shaft bearings?

Any PNs would be appriciated.

[SStrokerAce]

Comp Cams Pro Mags

That's an investment casting, in my experience you give away about 40% in strength with a casting compared to machining from bar stock.

I'm planning on something much lighter than the Comp part, more like the image I posted.

Last time I checked rocker arms, reguarless of material were all extruded to shape for proper grain flow and not just cut out of a block of billet.

I still think this is reinventing the wheel.

[SchmidtMotorWorks]

Last time I checked rocker arms, reguarless of material were all extruded to shape for proper grain flow and not just cut out of a block of billet.

Some people have claimed that but it really isn't posible. Crankshafts are a good example. It is true that a forging will be stronger than a casting of the same hardness but if you compare a properly processed billet crank to a forging the billet crank will generally be better. You can even see and feel it when you machine them. The forgings are much less consistant, even the universal LA forgings with lots of stock. you can see blotches on the sides of the cws when you cut them in a lathe.

Most forged cranks made by OEMs are forged flat like a four cylinder, then the middle two rod pins are twisted 90 degrees. If you want to see something ugly, magnaflux some of those cranks both when they are raw and when they are roughed in. A significant percent have cracks too deep to be finished.

Most rocker arms that are extruded have a grain that runs across the rocker arm rather than along it. This would be like making a rocker arm from slices of the cross section of a peice of wood. The grain structure couldn't be worse. The reason to use the extrusion is cost savings; not performance. Any claim that it improves performance is pure hype.

The there are the people that have tried to improve rocker arms and connecting rods from billet where the grain direction can be known (this is difficult to determine in modern metals). The only problem is there is no perfect solution in grain orientation to make a round peice with a hole in it stronger. In a rocker arm; making the grain ideal for the arm part weakens the area that often breaks, under the arm and vice versa, there is no win-win grain orientation.

Heat treating a finished tool steel rocker, con rod or crank does have some tendancy to make superior grain structure if the thick and thin areas happen to coincide with the stressed areas. This happens to work out better in some rocker arm shapes than others.

A good one can be seen at EPD racing.

As for reinventing... of course it's reinventing, millions of engineers make a very good living improving things that have already been invented.

[OldSStroker]

As for reinventing... of course it's reinventing, millions of engineers make a very good living improving things that have already been invented.

The rub is "improving" the product. Assuming you are an engineer and have the facilities to do the basic design, FEA, decide on appropriate material and heat treatment and mechanically test the newly improved parts to assure they are really better than what exists for a reasonable purchase price, I suggest that you are biting off more than you might be able to chew. Machining is probably the easy part.

FWIW, for the arm you have pictured, which may have some steel-on-steel rubbing, I'm not convinced 4340 or "using materials and heat treatment similar to billet crankshafts" is the best idea.

[SchmidtMotorWorks]

The rub is "improving" the product. Assuming you are an engineer and have the facilities to do the basic design, FEA, decide on appropriate material and heat treatment and mechanically test the newly improved parts to assure they are really better than what exists for a reasonable purchase price, I suggest that you are biting off more than you might be able to chew. Machining is probably the easy part.

I am fortunate to have FEA and my office is just a few steps away from the people that write the code for FEA software. I get all the advice I could ever use for free.

When I started making crankshafts in 84, I heard the same sort of doubters. People said "you can't make them that hard", "you can't make them that light", "you can't change the counter weight positions", you can't use oil holes like that" and on and on and on. Every single one of those doubters turned out to be wrong and everysingle one of those characteristics are standard now in billet racing cranks.

As for materials, I am still researching and the choice will depend mostly on whether I use a roller tip or not. At the moment I am leaning toward the roller tip however some fuel racers and NASCAR racers have argued against them. H11 or H13 is being considered now, this easy to cut material is convenient for me because I make my programs in the evenings, set up my machine in the morning to run unattended while I am at my real job five miles away. It is always a relief to see all the cutters are still in good condition when I come in to the shop in the evening.

[SchmidtMotorWorks]

I'm not convinced 4340 or "using materials and heat treatment similar to billet crankshafts" is the best idea.

Many of the pushrod tips and rocker adjuster screws are made of 4340, 48rc core, deep nitrided, just like some crankshafts. The preferred depth of nitriding for cranks has decreased over the last decade. I would probably stay deep.