The Stovebolt Site Forums The Shop Area Engine Shop Dressing rocker contact points

I thought I read somewhere that you could grind and polish the rocker where it contacts the valve stem if it is worn. Some of mine have small depressions in them where they contact the valve stem and I was considering doing this. Is this advisable and if I do it, is there anything I need to be aware of (besides getting it true and not taking off too much material)?

Most machine shops do this. They usually have some type of jig that produces a slight curve to the surface.

I asked a couple of auto machine shops around here if they did that kind of work, and most declined. Found one that said yes, and when I came back to pick them up, it was obvious that the shop boy had just taken them up to the grinder and had at it freehand.

I was not a happy camper, but had no real recourse except to take my work elsewhere.

I ended up setting up a jig and using my diamond sharpening hones to reface the ends. I ended up with pretty nicely polished curved faces. This was for the rocker arms on my Two Cylinder 1937 John Deere tractor, which maxes out at about 1100 RPM. It took a while, and I only had four to do. Twelve would have been 3 times the work.(haha)

Kurt

Yesterday I re-arced and polished 24 rockers for a 12 cyl Packard. A very common procedure. Been doing it 56 yrs. It's nice to have older/antique machines and tools for these jobs. David

David,

I would love to know how you went about it. Do you have any pictures of your setup?

Thanks,

Kurt

I have an attachment for my old Sioux valve grinding machine. Here are the instructions:

https://picasaweb.google.com/crenwe...Gv1sRgCIXI3pjjpLucaw#5698773529606842578

Two cones center the rocker where the shaft goes. There are different radius settings you can chose from. This is done by trial and error. You then move the rocker tip on the selected radius on a freshly dressed stone until the indented places are gone. Its nothing real scientific, but I've been doing it for years.

Uh oh. I just did this free hand the other day! Hahahaha! It came out fine though as I'm used to doing stupid things like this when I don't have the proper tool.

I did mine freehand a few years ago. Absolutely no problems. Just don't take off too much material.

I also have done close to one hundred free hand with no problems.

Well, I really didn't mean to disparage doing things freehand. Sorry about that. (In a past life I used to grind and polish telescope mirrors freehand). But I think there is a right way to go about using your hands which involves a lot of your brain.

Couldn't say the shop I took my rockers to used much of their grey matter.

Kurt

I kept quiet until now on this one, because I ignorantly did it by hand on three engines over 40 years ago (I did not have a shade tree but I was/am a shade-tree mechanic). Back then the good-old-boys dirt-track race-car mechanics told me that it would be OK.

I only have about 16,000 on the one engine that I still use (a 261). There was no wear on the rockers when I checked them a year ago.

I have been a shade tree mechanic for over 50 years. In fact I have a 1950 GMC with no motor sitting under the same shade tree where I worked on GMC and Y-Blocks 50 years ago. About the time i got out of high school, and old shop closed up and I bought their Sioux valve machine with a rocker attachment as well as a stem truing and chamfering . So I was the first kid on the block to have uptown machine tools. I know lots have been done freehand, but I can't help but think that having the rocker tip parallel with the shaft has got to take stress off of the rocker bushings. Back when my father delivered gasoline with GMC, we might go through 3 or 4 new short blocks with the same rockers. That must have been around a half a million miles. We always had the rockers dressed at every valve job. However, none of our engines, except for maybe Cletis, gets driven that much any more.

The stovebolt rockers will take a lot of truing, but don't try the same procedure with the stamped rockers on a V-8. Those rockers are casehardened, and it only takes a tiny bit of grinding or sanding to break through to soft metal. Fortunately they're like a bunch of baby chicks- - - -CHEEP-CHEEP-CHEEP- - -so I usually replace the rockers and pivot balls anytime I rework a set of small block heads if they're showing any wear at all.
Jerry

i did mine on the 235 in the dump. i took just enough off to remove the marks and then polished them back up using a dual scotch brite pad/fine sand paper roll on a drill. i tried to keep the same radius i figured in time it will wear in to where it wants to be.

next time you come up this way bring that 50 with you ive got the perfect tree to put it under.


i wonder if cletis ever looked at his yet

This brings to mind another question, and that is since the contact point of the rocker arm has a radius to it, wouldn't that make it difficult to get an accurate reading with a feeler gauge? I just looked at mine and the contact points are concave, like a hollow. If that is the way they're supposed to be (and I sure hope they are) then it seems like you couldn't really get a true reading with a feeler gauge.

That contact patch is supposed to be convex. If yours is flat, or concave, it's worn. That's the whole reason for having the tooling on the older Sioux valve grinders, so a rocker arm tip could be re-radiused during a valve job. When casehardened stamped rockers got popular, the rocker refacing tooling was not included with the valve machine because the hardened rockers were not supposed to be dressed at all.
Jerry

When your rockers are worn, and you can't get the feeler gauge in there, you just cut down the feeler! Not that I would have a set of feelers like that, hahaha!

Is a rocker that is worn like that fixable? I'll try to post a picture later tonight. If anyone's got a picture of what the radius ought to look like, that would be helpful.

That's what we've been discussing- - - -there's an accessory for some of the older valve refacing machines that's designed to accurately re-profile the tips of some types of rocker arms. Yes, stovebolt rockers can be re-radiused if the equipment is available. Try an oldtime auto machine shop- - - -they might still have the equipment, and somebody who knows how to use it.
Jerry

After I made that post I went out and took a close look at my rockers. They're not concave. That must have been an optical illusion. Once I got them under a strong light and put a straight edge on the surface, I could see that they're actually convex with a radius. There is a slight depression in them where they contacted the valve stems but I'm glad to report they're not actually concave. They looked that way in the dim light of my garage, just taking a quick glance.
Anyway, they look very fixable.

Denny Graham,
There's another factor in valve train geometry beyond those you mentioned. Rocker arm pivot center. All factors together will give you the advertised lift, timing events and minimize guide and stem wear. These rocker arcs is part of that blueprint process. It won't matter much on most engs here,true, but If you're refacing rockers,why not at least restore to factory arc? The machine will also keep the pad square to the stem tip. David

As I am planning on making a high lift set for myself one day determination of the ideal radius as well as its position relative to the shaft bore has been something I have been on the lookout for. Then it hit me this morning.... Checking a worn one in the CMM (coordinate measuring machine) will tell me both those things exactly. The depression that is created from use is not only wear but actual burnishing or compression of the rocker which usually increases the surface hardness. When touched up if only the high spots or displaced material is removed leaving the center or actual contact patch alone there is a possibly that the hardness in that area exceeds a new one.

Yes.I've done them on a drill press table using a sanding drum by hand.Nice sweeping motion,the machined side of the rocker maintains "straight" finish.

My machinist showed me what to do and I did it on an drum sander chucked in my drill press.


Tim

Mr Panic,
Probably anything your doing on your engine doesn't require valve train esoterics. I didn't mention this on my Thu 6:59AM post for that reason. The rocker pivots on the shaft so the tip/pad travels in an arc. It doesn't push straight down on the valve. It's critical, for those that understand the full implications,to equalize the outward side force against the stem during the first part of lift and the pull towards fulcrum during second half. A lot goes into a correct setup. As mentioned, the refacer operator's experience has much to do with using the machine. He can alter that arc and its center depending on cam, pushrod's length,stem height, rocker ratio,etc. Your idea of rotating valves by angle grinding doesn't fit into any physics. I'd be curious to see your explanation. David

Valve rotation can be accomplished if the rocker only hits the edge of the valve. The rocker tip will try and pull the valve stem with it, thus turning it.

Think of a lawn mower self propel unit that uses two wheels, the smaller drive wheel with a horizontal axle runs on a larger driven wheel with vertical axle. By moving the small wheel closer or farther from center, the larger wheel spins faster or slower. Now change the smaller wheel to rocker tip, in its full range of motion, it follows a arc, which is just a small piece of a circle, so unless the rocker is right over the center , it going to rotate the stem.

Its true can can alter the start stop points of the arc, but the differences would be hardly measurable. The side to side (level) far out weighs the starting/ending points. The rocker ratio is set by location of the pushrod and the pushrod length only changes the length of the arc. A proper designed and ground rocker, will only use a small portion of the valve stem with a low lift camshaft, not even half the stem width. If you find a valve stem with a wear line across the face, you can bet the rocker is worn since the valve quit rotating.

Joe

David, your grasp of this subject is not as thorough as you believe it to be. I'd explain, but you'd just be rude again.

Panic,
You're totally wrong in all your thinking. I didn't think there was rudeness conveyed. Just trying to enlighten.Sorry if any offense taken. Just letting you know there's much going on in the valve train than most think. You have your opinions and ideas, I have to work with engineering and physics facts. Innovation is exciting, too.I don't hold National Championships at Daytona, Monterey, Superbike circuit, build for Indy, etc,without knowing a little bit. True , I'll never know it all and I'm always open to learn, even in my 8th decade. Keeps you young. David

Joe H and Panic,
It took me a while but I finally realize you're both having fun "pulling my leg" with these insane posts of yours.I must admit, they're quite the concoctions.Thanks for bizarre. David

It’s probably safe to say that individuals with this experience will soon be extinct. Assuming the machine has adjustability how does the operator determine the required arc and position? Does he set it up to get close to the existing wear pattern? If the rocker pad is not parallel to the head face (front to back) then I could see how the off center contact would attempt to rotate the valve in the same way that this offset contact between cam lobe and lifter induces rotation. Perhaps you folks are not on the same “plane”.

Try the Rocker Arm guys in Anderson, CA. They do it and also completely refinish to stock (or High Lift spec's.) on any assembly. I use them several times a year and they do require a core charge that is refundable when the old set is received at their shop. Good technicians and great work accuracy.
Normbc9

On my old Sioux machine, two cones align the rocker. Therefor the rocker face will be parallel to the shaft, and I think that is what is important. The attachment has has about a half a dozen radius to chose from. I do this by barely touching the stone while I rotate the rocker. When it contacts the surface the same in front as in back I consider it the correct radius. I have never seen a machine that uses a more scientific approach to the radius, but I'm sure they are out there. But I think my method is close enough for a stock GM engine that is 50 to 75 years old. Here are the instructions for the attachment. Possibly this will explain better how I do it.

https://picasaweb.google.com/crenwe...Gv1sRgCIXI3pjjpLucaw#5698773529606842578

That's exactly how all of us who bothered to learn the concept did it with untold thousands of rockers, and they worked very well. It's just more fun to get hyper-technical and try to impress the great unwashed mob with pseudo-intellectual Bovine Scatology when the keyboard lends a certain amount of anonymity to one's comments! If that stuff could be loaded up and trucked to market, they could make a fortune selling fertilizer.
Jerry

Some 12 year old has evidently gotten David's password, and is making a complete fool of him.

Pseudo-intellectual Bovine Scatology . . . Man, that's a good one. I am a little "cowed" by all this technical lingo.