why stainless steel rocker arms?
 

I was pondering this recently- why choose stainless steel for a rocker arm material and not another steel alloy like 4140?

because stainless is pretty!

i can tell you that the crower ss rockers will take years of abuse.

Stainless wouldn't rust,

That's the only reason I could figure, but then again many other engine components are alloys that will rust and they aren't an issue.

Just personal preference, but I would rather run stainless than aluminum.

Me too, and that's what Bob put in my engine.

I'm just wondering why they didn't choose a stronger alloy. One could heat treat 4350 steel well north of 150ksi yield and wind up with a nearly indestructible rocker that would probably be cheaper than SS.

After some review, the Jesel steel shaft setups aren't stainless.

I've used the Comp Pro Magnums ( 8650 Chromoly ) without any failures. They claim 5% lighter at the valve than aluminum , long cyclic life.

The last set of crane gold aluminum rockers i replaced , went from 1985 to 2011. Out of 32 rockers, 2 had cracked trunnions. The trunnions were steel, not aluminum.

Steel bodies certainly have a higher cycle life. The bearings still wear though.

Icdedppl had comp cams steel rockers, the older ones . The geometry was awful with them. And they were no stranger to failure. Lots of guys had issues with breaking them, im not sure how the new XD series are.

All rockers are not the same. The comp steel, scorpion alum, and crane alum, all had a different measurement from center of trunnion to center of roller tip, even though they were the same ratio.

When i first put my engines together, i went with a pushrod that gave me a pattern that was most centered on the valve stem, because thats what i was told to look for. Simply a centered wipe pattern.

After 2 seasons i took things apart after reading up on the mid lift method. My setup had been throwing away a substanial amount of valve lift after measuring with a dial indicator on the retainer! Pushrods were too short. Sure it ran fine, but.....

Sorry for getting off topic, but i think theres more to rocker arms than material.

Well price has alot do do with it. Cast vs. billet, I prefer a thicker billet aluminum piece over a thinner cast metal piece. And once again I agree with Mild Thunder, there is more to it then material.

You can make a rocker arm out of super duper nasa specd space age steel, but theres still bearings in them, and most rocker failures ive seen, have been from a failed bearing or trunnion . Rarely do the bodies snap, unless of course your binding springs, or some other valvetrain follies

Now start talking 800 plus pounds of open pressures , higher ratio rockers,big rpm and thats another story. A mild marine hydraulic roller, 1.7 rocker, ehh.

I think we often overlook whats worked for many decades , and fix problems that dont really exist. If reliabilty is a concern, much of that is in the cam design, springs, lifters, etc. Stick an aggressive high jerk lobe in your engine, and its gonna beat chit up irregardless.

No matter whatever material they are made of. The complete valve train has to be set up properly. I can't count the times I have seen on high end and stock motors where the valve train needed more then just a little attention. Wrong push rod lengths, roller tip hanging half off the valve stem, incorrect rocker stud, springs not setup right etc............. Then a rocker breaks, and there it is blame the sob rocker.

Well Mild, I don't foresee ever ever ever building a marine motor for myself with that kind of open pressure...LOL I personally like Hydraulic roller cams in my own motors.

Aside from the rocker issues on the 525efi engines, which may have been a bad batch of bearing cages, or , the lack of spring pressure on the 525s, i dont know of many rocker failures on merc racing engines.

The 400hp, 420hp, 440hp, 450hp, 460hp, 465hp, HP500, 500efi, 575, 600sc, 800sc, all used a crane alum rocker.

Not suggesting its the best, but, its what i use, and will continue to use. Only problem is they are running low on stock on them everywhere currently !

I see you have been reading up MT ^^^^

maybe inside joke OEM manual ???

Your spot on. Our automotive BBC 12 deg Cylinder heads wound up side loading during the opening process on the same cyl (wiping out even on a shaft rocker trunion) .. Thanks to my engine guy we started using offset .001+ or - on the push rod tip end to solve the issue. Who would have thunk that eh? Im liking the stock marine set ups that are forgiving .

Don't forget the 370hp

i just want to say don,t be afraid of the scorpian endurance arms and all they make is made in the usa with american materials.i will spend a few xtra bucks to buy american made parts.

Just curious, can anyone actually answer the posters question,

hope so, I have them... lol

I don't know the reason but I think it might have to do with the heat treat process.

or the weight maybe

Steel rockers tend to be recommended for serious valve spring pressure where in open pressures are 800lbs and beyond .. I've ran crower on shaft set ups the went back to jesels for offsets at the push rod tip . Just strength for steel and stainless .. Trunion is still another conversation and most mfg will rebuild your rockers

I would think it's just an option for corrosion resistance. Under the valve covers is where you'll find any condensation, whether it's from a little reversion, or just a cold block and not enough oil temp. This time of year, every engine I dyno ends up with a little milky oil under the breathers, and bottom of the fill plug just from the air temp.

this would be a good question for a metallurgist. is it possible that it has to do with elasticity or some such thing? I would think that the metal used would need to have a minute amount of give in it vrs something super hard that would tend to crack over time.

I wish Dave Crower was still around, maybe he could tell us why they starting using stainless about 30 or so years ago.