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what steel for rocker arm shafts and pedestals?

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arse_sidewards
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Joined: Mon Jan 21, 2013 7:18 am

what steel for rocker arm shafts and pedestals?

Post #1 by arse_sidewards » Fri Apr 07, 2017 3:10 pm

I have some 2nd hand shaft mount rockers I'd like to put on my 300. There isn't really space for individual shafts so I'm going to use one long shaft. The rockers are set up to use needle bearings on a 3/8 shaft. O1 drill rod is dirt cheap in the required size and length but I'm not sure it will be hard enough (after tempering).

I will have one long mount/pedestal that bolts down to all the rocker arm bosses and acts like the bottom half of a 2pc split shaft collar and will support the shaft on either side of each rocker while being tall enough for the bottoms of the arms to clear the top of the cap screws holding the pedestal to the rocker arm bosses. I'm planning on make the pedestal(s) out of A36. The caps (basically identical to the top half of a split shaft collar) can be made out of something stronger (I'll cross that bridge when I come to it). Does A36 for the rocker shaft pedestal sound appropriate? Could I get away with aluminum?
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

pmuller9
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Joined: Tue Aug 06, 2013 12:33 am
Location: Columbus, Indiana

Re: what steel for rocker arm shafts and pedestals?

Post #2 by pmuller9 » Fri Apr 07, 2017 3:24 pm

Stay with the A36 steel for the base cradle. There is no need to save weight and lose strength by using aluminum.
Properly heat treated 01 tool steel (oil quenched) will have a Rockwell hardness just above 60 which is the same as a good push rod end.
Should be no problem with wear resistance
I like your design. The rockers are obviously adjustable?
Keep us posted.

arse_sidewards
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Joined: Mon Jan 21, 2013 7:18 am

Re: what steel for rocker arm shafts and pedestals?

Post #3 by arse_sidewards » Wed Apr 19, 2017 1:57 pm

pmuller9 wrote:Stay with the A36 steel for the base cradle. There is no need to save weight and lose strength by using aluminum.
Properly heat treated 01 tool steel (oil quenched) will have a Rockwell hardness just above 60 which is the same as a good push rod end.
Should be no problem with wear resistance
I like your design. The rockers are obviously adjustable?
Keep us posted.


Yes, they're adjustable. They're some Jesel 2:1 NASCAR stuff I bough used for under $100 a few back. My intention is to try them out with the stock cam which I have every indication they'll play nice with. I'm not too worried about metal fatigue in my application, speed, spring pressure, etc, etc are less than half of what they'd see in the kinds of applications they're marketed toward. If possible I'm going to use an off the shelf valve and push-rod but since I might step up to 3/8 or bigger (mostly because of length, not spring pressure) that could very easily go out the window.

The "just use steel because strength is what matters here" is basically what I expected for the pedestals.

The reason I asked about O1 is because these rockers use needle bearings? Is O1 suitable for that sort of use? I see the Rockwell hardness of 50 tossed around a lot in discussion of bearings. I also see a lot of people saying that's the minimum, depending on how demanding your application is you may need more. The bearing speed will be fairly low but most of the force will be concentrated in one spot on the shaft and the rollers will all ride in the same place for the most part, it's not like a gear set where wear will be spread out evenly. I'm worried about the needle bearings eating the shaft since they're going to be lubricated via oil splash from the push-rods and once I get this done I'm probably not going to open it up for years. I had considered pressing in bronze bushings to replace the needle bearings then running the rockers on a drilled shaft with an oil supply (fun fact, with some lathe work a .22 barrel would have been about perfect) but that would be a lot more work for not much benefit and introduced other complications.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

pmuller9
Registered User
Posts: 3358
Joined: Tue Aug 06, 2013 12:33 am
Location: Columbus, Indiana

Re: what steel for rocker arm shafts and pedestals?

Post #4 by pmuller9 » Wed Apr 19, 2017 4:03 pm

01 tool steel should harden out to Rockwell 62 to 64.
I don't know of any performance surface within a race engine that is harder that that.
We had a set of pushrod rod ends that gave us wear problems that was tested at Rockwell 40.

The next set from a different company tested at Rockwell 60.
We check our rocker clearance every other race and never have to adjust.
That is with 800 lbs open pressure operating at 8 minutes a race.
We use T&D steel rockers.

arse_sidewards
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Posts: 846
Joined: Mon Jan 21, 2013 7:18 am

Re: what steel for rocker arm shafts and pedestals?

Post #5 by arse_sidewards » Wed Apr 19, 2017 4:38 pm

pmuller9 wrote:01 tool steel should harden out to Rockwell 62 to 64.
I don't know of any performance surface within a race engine that is harder that that.
We had a set of pushrod rod ends that gave us wear problems that was tested at Rockwell 40.

The next set from a different company tested at Rockwell 60.
We check our rocker clearance every other race and never have to adjust.
That is with 800 lbs open pressure operating at 8 minutes a race.
We use T&D steel rockers.


Well that settles that, material properties are not something I have much experience with.
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

arse_sidewards
Registered User
Posts: 846
Joined: Mon Jan 21, 2013 7:18 am

Re: what steel for rocker arm shafts and pedestals?

Post #6 by arse_sidewards » Mon Jun 26, 2017 8:32 am

So I'm picking up a mill this Friday and in the spirit of getting ahead of myself I thought I'd ask about how best to machine the pedestal.

What tool should I use to cut the groove in the pedestal that the rocker shaft will be clamped into?

I'm thinking I could use a ball nose end mill but am concerned that it would cut oversize by a thou or two and the bottom half of the shaft would only be supported/clamped across a small area. Am I over thinking it or is there some other way I should be cutting this?
1994 F150 4x4 8ft, engine is basically stock.

66" leafs, extended radius arms, lockers in both ends, nothing special.

pmuller9
Registered User
Posts: 3358
Joined: Tue Aug 06, 2013 12:33 am
Location: Columbus, Indiana

Re: what steel for rocker arm shafts and pedestals?

Post #7 by pmuller9 » Mon Jun 26, 2017 2:02 pm

Use a ball end mill that is smaller than the finished diameter.
Mill the rocker cradle.
Then mill the same trench in a corresponding size steel bar.
Sandwich the two together so there is a round hole that can be finished with a long drill bit.

Instead of making a single long unit, you may want to look at the possibility of two or three shorter units.

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