The Stovebolt Site Forums The Shop Area Engine Shop Grinding rocker arms

A few weeks ago in a horse trade I got a Sioux model 2100 valve facing machine, along with the tools for grinding valve seats. Anyway, I have a Sioux model 672A attachment for grinding the rocker arm tips. Does anybody have any pictures of how it attaches to the valve facing machine. I know it works on the valve stem grinding end.
Thanks
Dave C

There are several Sioux instruction and parts manuals on Ebay. The closest I see to yours is a Model 2075. It's on a CD for $5.00. I have used that attachment many times, but it's been so long ago I'd just have to figure it out by trial and error now.
Jerry

My old Sioux machine has a rocker re-facer which I haven't used in years but the flathead Ford fixture for cutting stem to the correct length gets used a couple times a year. The adjustable lifters are way too heavy for a performance engine. My instruction manual got flooded so glad to hear they are on ebay. I had an ancient Black and Decker dry machine with a rocker attachment that put an absolute mirror finish on rockers or valves but you had to wait till parts cooled before making a final cut. The founder of Sioux Tools, Oscar Albertson, was my Dad's great uncle and had him do dozer work for the new building pad maybe (?) in the 1940's.

Any chance you could post a photo of the machine and the rocker reface tool/accessory. I have never seen one.

The rocker refacing tool for my Black & Decker valve grinder is stashed away somewhere- - - -haven't used it in years! I've found that a piece of 400 grit stick-on sandpaper for my 6" disc sander does a much better job of refacing rockers than the fixture for the valve grinder does. It just takes a little practice at following the contour properly freehand.
Jerry

It tells me the "Contact travel" on the rocker arm is far less than what I had expected. The contact on the valve is less than I expected but by not as much differance as the former.. That's a valuable drawing... too me ! I beg to differ on the value of the jig in determining the radius. That's why I bought one. I saw it used alot when I was a kid. I worked after school for an aircraft mechanic. He ground the rockers on those aircraft engines when he overhauled them. I just haven't quite figured out how it attaches yet. But I will when I have more time. I just.thought someone might have a picture. If you do. Please post. If not. $%× up.

How about going one better than a picture. Do a search on "rocker arm grinding" and then click on the "Ford rocker arm" video. It shows the tool in position and the actual grinding of the rocker tip. We used to do more Y-block Ford rockers than all others combined.

I will look that one up. Thank you!

So David C., the guys here are trying to help you out and you tell them to $%x up! That’s rather rude and we here at Stovebolt try to be respectful of others opinions. Have a cup of coffee, take a deep breath and

There's a lot to be said for the level of experience of the operator of any machine tool. Today's machinery with a computer controlling every part of the operation has created a couple of generations of button-pushers who are basically playing video games and letting the machine do all the thinking. It takes a few brain cells to rub together and watch the progress of the resurfacing to follow the contour of the original shape and only remove enough material to get the surface smooth again without making a change in the original shape. Back when an automotive machinist might rebuild several sets of heads a day with those types of rockers just to pay the rent and put food on the table, he kept those skills honed to a fine degree. The fact that we're even discussing the procedure at all is a sad commentary on just how dumbed-down engine builders have become. "Buy new parts - - - -install- - - -hope for the best!"

Once the rockers are smoothed up, the best way to prevent further damage is to keep the valve adjustment correct. Mechanical lifter camshafts have an area of slow lift ground into the lobe called an "acceleration ramp" where the manufacturer's specified lash is slowly closed up before the valve actually begins to be lifted. Let the clearance get a little excessive due to ignorance or negligence, and the remaining clearance is taken up by the cam lobe violently slapping the rocker arm against the tip of the valve. The result is noise, and rapid wear.
Jerry

Look at the diagram you sent! The radius of the grind is determined by 1 thing. R1 distance , because the rocker is fixed to rotate in the same axis as it does when assembled on the rocker shaft..! The variable is "HOW MUCH" you grind. Entirely up to the operator. But , the outcome or radius will be the same. The diagram that you sent also makes it clear that it is not that critical what the radius is as long as it is not flat and the area of contact is approximately the same. Furthermore, I believe if you look at the geometry of the whole assembly, you will realize that the area of contact is likely also influanced by the cam lift.

I have a question related question to this discussion.

I'm assuming there must have been some type heat treat applied to that radius - in order to increase surface hardness and reduce wear.

Is there any concern about grinding through that layer and exposing softer metal? Or is the depth of the heat treat usually deep enough that this is not typically a concern?

Grinding rocker arms obviously works because people have been doing it forever, but the TM I have for the GMC 270 says to toss them if they are worn - not grind them.

Would be interested to hear your guys thoughts on this.

p.s.

Panic, that is an AWESOME print! Thx very much for sharing it.

I am sure they are hardened. But , we all sharpen drill bits, planer blades, crankshafts etc. ,correct. Furthermore the machine I have has a flexible line to cool/ lube the rocker as you dress the end. I defer to Hotrod to be the expert in that area.

Never mind

Let's assume (yeah, I know what that means!) that we're discussing stovebolt Chevy rocker arms. They're either cast or forged, not sure which. The only way to "harden" the surface of most castings is with a process known as "case hardening". Us gunsmiths and most blacksmiths have been doing that for a few centuries, long before automobiles came along. That rainbow color pattern seen on some antique firearm receiver dastings is a result of a variation of that process called "color case hardening" It's not much harder than the underlying metal, and it's microscopically thin. A stamped steel alloy rocker like a small block Chevy V8 uses, and a lot of others can be hardened to have a much tougher surface than a casting or a forging. I would never, ever try to resurface a ball-pivot SBC rocker- - - - -once the surface hardness goes away, it would wear very quickly. I believe the "do not resurface" rockers the GMC service manual is talking about are also the stamped steel type. Cast/forged rockers are much more forgiving when it comes to resurfacing than the stamped ones.

Once we get away from the original geometry of the factory valve system with radical valve lobe lift, different rocker arm ratios, and other non-OEM bits and pieces, things really get confusing. I've spent lots of time measuring and tinkering with things like pushrod length, rocker arm angles, rocker tip sweep across the top of the valve stem, lash caps, etc. Those engines usually lasted less than a thousand miles before they either wore out, blew up, or got rebuilt!
Jerry

Speaking of case hardening, it can be done with an OA torch with a carburizing flame (a yellow trailer past the blue part). Not sure I'd try that on rocker arms though.
I did that once when I built up the brake pin slide surfaces on a Model A. They are just plain steel and after eons of use get a divot worn in them, which cause the brakes to be even more inadequate than they normally are. I built them up with a torch and was going to mill them down smooth, but the cutter wouldn't touch them. I wound up smoothing them with a Dremel grinder. It worked and I had the best mechanical brakes of any Model A around at the time.

The perfect profile on a rocker arm tip would have to be ground somewhat like a gear tooth involute pattern. But more complicated for sure.

I use "air hardening drill rod" as welding rod and a torch to build up parts that have to be tough as woodpecker lips on gunsmithing projects like repairing a broken firing pin tip, etc. Apply it with a torch and shape it with a grinder, as it absolutely can't be cut with machine tools. Once the part is ground to the proper shape, then I "draw" the finished piece by heating it in the torch flame to a straw color and letting it air cool to avoid making it brittle as glass.
Jerry

I have some stellite welding rod I should send you

Too hard- - - - -drill rod and other high carbon steel alloys can be annealed and tempered to any stage of hardness/toughness needed for different applications by some judicious application of heat and/or quenching in various cooling media- - - -air, oil, water, or even sand. Stellite makes great exhaust valve seats for engines running on "dry" fuels like Natural Gas or LP, but it's far too brittle for most other applications. I have made some very long-lasting lawn mower blades by building up a layer of hard-facing welding rod on the cutting edges, though!
Jerry

Jerry,

The rocker arms as referenced in the TM appear to be forged, but I'm not 100% sure. However, since it is an Army TM, I'm thinking perhaps they were a little less worried about the cost of repair to the customer - hence the "discard" recommendation.

Your firearm example is well taken. I know that the heat treatment of many firearm receivers is a critical factor in their performance - with the idea that the outer surfaces are hard in order to to resist wear, while the inner core remains more ductile. This often extends beyond case hardening. If you're into old firearms, I'm sure you know the story of the "low number 1903 Springfield rifles", and the potential ramifications of improper heat treatment. For those who may not, during WWI, as production was ramping up, many were improperly heat treated - causing the receivers to be brittle and ultimately break into multiple pieces when fired. Obviously not good for either the rifle or the shooter.

That's kinda what led to my original question. If the base heat treat process (as opposed to case hardening) inherently left the surface harder than the core. If there was a surface hardening of some type applied. Or if the metallurgy was consistent all the way through the cross section of the tip. Base on everyone's experience, it sounds like its probably the latter.

As you also mentioned, stamped rockers like on the small block Chevy are extremely hard at the friction surfaces. I'm betting that the steel they use has to be fairly ductile in order to make it thru the stamping process, which dictates the application of a surface hardness treatment at the major wear points.

I'm probably over thinking this way too much. I think that I'll just shut up now, grab my belt sander, and go refinish some rocker arms...

Best Regards...

Bob

Some years ago, I can't remember how many, I resurfaced my rockers because they at up two feeler gauges every time I adjusted the valves. I used the HRL "offhand" method of grinding on my belt/disc sander. I have also done that to "cone/radius" valve lifters, per Bruce Crower. Anyway, 50,000 or so miles later there is no appreciable wear on the rockers. So, they must be made of some hard stuff. I'm using stainless valves and bronze guides.

On my "breathed upon" Norton motorcycles I have used lash caps as the only way to keep the ball-shaped rocker end from digging a hole in the valve stem. Easy to change lash caps, big deal to resurface valve stems. But the extra weight does cut the top RPM by a couple hundred. Not a problem on my 235.

Bob, I've seen two distinctly different designs of rocker arms used on GMC engines. One type appears to be either cast or forged, and look almost like Chevy rockers. The other type is obviously assembled from multiple pieces of stamped steel spot-welded together, with a rounded pad at the tip that contacts the valve stem. I'm not familiar enough with GMC engine variations to know if there's any rhyme or reason about which type of rocker was used on any specific engine. I'd have no problem with refacing the one-pierce rockers- - - -not so sure about the assembled ones!

Here's an example of the stamped steel GMC rockers - - - -not sure how long the Ebay auction will be there, and yes, moderators, I understand why posting links like this are discouraged. I'll go ahead and slap my own wrists!

https://www.ebay.com/itm/1939-1941-40-1946-GMC-Pickup-Truck-228-248-270-302-Rocker-Arm-Shaft-Tappets/113838395870?hash=item1a814c11de:g:wYQAAOSwlk1dQgft

Jerry

Hi Jerry,

I have seen pictures of type also, but have never actually seen one in person. Not sure either if they were unique to a specific era, model, displacement, etc.

I was tempted to think that perhaps they came later than the cast/forged rockers (maybe as a cost savings?), but if you look at the rocker arm shaft support brackets in that listing, they are cast aluminum. I believe those came first, followed later by the stamped steel brackets. Although its also very possible that assembly was put together from multiple sources some time it its history.

If any GMC guru on this forum is reading this, perhaps they can shed some light on this.

Best Regards...

I helped a Tennessee forum member who used to post a lot a few years ago assemble an oddball GMC engine, a 256 cubic inch that supposedly was used in WW II Canadian military vehicles. It had a set of those stamped steel rockers. The 256 had a 248 crankshaft and a 270 bore. Those are extremely rare engines, and it was not original to the truck he was restoring, a 1951 long bed pickup that had belonged to his father.
Jerry

Stamped steel assembled rocker arms reeks of wartime ingenuity. Even though it may have been more labor intensive, it would have saved scarce raw materials. During wartime, labor is low priority when dealing with scarcity of raw materials.

Slant 6: same thing.