The Stovebolt Site Forums The Shop Area Engine Shop Worn rocker arm shafts- - - -

One of the inevitable consequences of inadequate oil flow to stovebolt rocker arms is worn rocker shafts. For some reason, the rocker arms themselves don't seem to wear as badly as the shafts they're mounted on. Intermittently, new replicas of stovebolt rocker shafts are available on Ebay, but the supply is far from steady, and the prices are fairly high at times.

Here's an intererting factoid- - - -only the bottom of the shaft wears, due to the upward thrust of the pushrods, and also the tension of the valve springs. "Simple solution- - - -just turn the shafts upside down, and let the rockers run on the unworn part". Not so fast- - - - -there are oil holes in the shafts that need to point down- - - -turn them up, and the rockers don't get oiled properly. However, here's a sneaky trick- - - - -use a solid carbide drill bit, a V block, and a drill press, and drill the oil holes all the way through the shaft. Then thread the top holes, and use brass Allen set screws to plug them. With a litle creative file work it's possible to use the brass plug to stabilize the rocker, letting the plugs stand a little proud of the worn areas. Be sure to find and fix the cause of the restricted oil flow to the cylinder head while you've got things apart.

No, it's not a perfect fix, but the above procdeure can be employed to salvage a set of rocker shafts that might otherwie have to be scrapped.
Jerry

Let me ask the obvious question. If you need carbide to drill the shaft, wouldn’t you need carbide taps to make a thread?

Anneal the area around the original holes with a quick application of an acetylene torch flame, if necessary. The surface hardening will probably be worn away already. I'm about to try this on a set of junk shafts I was about to discard, so it's possible a carbide bit won't be needed to cut the shaft material. If a file will scratch it, a high speed steel bit or tap will cut it. Just thinking out loud on this one- - - -haven't tried it yet.
Jerry

Possibility of using Torrington bearings on each rocker arm, Jerry? Too hard to seal them so as to provide oil to the push rod ends?

I’m not even sure these things were surface hardened to begin with. I’ve got an old worn set somewhere I can check out.

A variation of Jerry’s idea: Might be able to do the same “flip and drill” concept, but apply some sort of high tech (application correct) epoxy or such to fill up the old grooved out areas. Sand back to round with some emery cloth. Probably last a long time if you make sure they get proper oil supply.

Jon, I don't think the rockers could be machined out big enough to accommodate a needle bearing, but a thinwall bronze bushing is a definite possibility. Use two bushings, one pressed in from each side, to form the lube slot to the spit hole on top. Detriot Diesel connecting rods use two wrist pin bushings with a slot between them to supply the cooling oil spray to the underside of the piston crown. I believe some GMC gas engines also use a gun-drilled connecting rod and pressure lubed wrist pins with a slot between the bushings.

JW, I just bought a Eutectic spray-weld setup that can be used to build up crankshaft journals, and one of the powders that came with it is a "hard-facing" material. That could be used to repair the worn spots, and the shafts reground round with a tool post grinder in a lathe, but at some point, the labor cost would exceed the worth of just buying new shafts.
Jerry

Just curious, Jerry. Some of the sealed needle type are only about 1mm thicker than the ID and have oil holes in them, but if the shaft was already worn you might have trouble getting them to seal right. If you had a new shaft at the same time, setting it up that way might take you far into the future. We've talked about thinwall bronze inserts before and those as you mentioned would be okay. When you flip them bottom/top you'll still have the same loss of oil/oil pressure and all, though.

If there's even a trickle off the rocker tip to the valve stem, that's all that's really needed. I'm pretty sure a lot more oil flows at highway speed than we're able to see at idle with the valve cover off during an adjustment procedure.
Jerry

I'm away and can't measure at this time. What is the OD of the shaft piece, Jerry?

Jerry..
You'll love the Eutectic setup. We used it on the farm to harden trencher teeth, plow points, chisel plow teeth and peanut digger points. Much better than hardrod, less heat to crystallize the steel and promote snap-off of the tip.

Just a little under an inch, I believe, Jon. The shafts are stashed away where they're a little hard to reach here, too!
Jerry

My caliper says the rocker shaft is 0.992-0.993

The roller needle bearing idea is cool. Probably ridiculously overkill….but cool. The style of needle bearing that manual transmissions use, is pretty loosely caged and would not impede oil flow. Jon, were you thinking of turning down the shaft to accept the bearing?

What we probably need out of this brainstorm is a method that an average guy with average tools could do, for less than the price of new shafts. Jerry’s original idea is in that spirit.

Once I get about half a dozen other projects closer to finished, I'm going to try modifying those junk shafts. At least they will be sacrificed for a good cause it it doesn't work. If I succeed, we can add another tech tip to the collection. Right now, I'm getting ready to make a special tool for the foundry where my son is a machinist, and they're making my bank account really healthy in the process. Love it!
Jerry

Turning down the shaft would be a possibility but we'd then have to machine a bushing for the standpost to make sure everything would fit. Some of the roller bearings are sealed but you must have a nice round shaft. I like the idea...they'd be replaceable and they wouldn't cause the shaft to wear oddly. Plus you'd shed a bit of friction in the process...I'd have to do some coefficient work but it would be there. As long as too much wasn't removed from the shaft (which could weaken it), it should be okay. But really the valve springs on a stock Stovebolt aren't that much.

I just ordered a few of these- - - - -

www.ebay.com/itm/204380274310?

Give the shafts a ground finish to the right OD, and a quick surface hardening job with Kasenit- - - - -and ream the rocker arms for a slight press fit- - - - -worth a try!
Jerry

With that style bearing pressed into the rocker, how will the oil get to the needle bearings?

Definitely worth a try, Jerry. I'll be curious!

I would think you’d have to drill a hole of some sort in the bearing cage.

Edit: I read your question wrongly. The oil gets to the needle bearings just as it it oils the OD of the rocker without the bearing. The issue is getting enough dribble OUT out of the needle bearing, through the weep hole that lubricates the rocket tip.

The same way it gets to the rockers now- - - -from the holes in the shaft. It might be necessary to drill a tiny hole in the bearing cage aligned with the weep holes in the rockers to let some oil dribble out , to keep the OCD guys happy- - - -maybe .020" or so.
Jerry

Slight variation of this same idea. Use this style of roller bearing:

https://www.rigidaxle.com/products/needle-kit-nk-nv4500

Oil would flow more freely through the rocker weep holes and such. I don’t know if this style can be sourced in the appropriate dimensions, however.

Looking at the bearing catalogs last night I saw where some of the sealed needle bearings had holes in the cages. Example:

https://images-na.ssl-images-amazon.com/images/I/71L3hwBuk1L._SL1500_.jpg

I think there would need to be some degree of sealing to help with oil pressure loss. Either that or choke the oil supply hole down so there would just be a trickle. That's one of the problems when the shaft wears...you will get a bunch of oil pouring out of each rocker arm.

I drill a hole in the outer cage of the Torrington bearing I use at the top of a stovebolt distributor housing when I do the "zero wobble" modification by pressing a hardened steel sleeve over the shaft and fitting a needle bearing to the housing. Thr hole is there to allow grease from the cup to enter the bearing.
Jerry

The springs on the shaft, along with a close fitting steel washer riding against the rocker arm will provide plenty of resistance to excessive oil leakage. We' don't need a perfect seal, just slow the flow down long enough to lube the rockers. The pressure inside the rocker shafts is very low to begin with.
Jerry

I've been following this thread, and the needle bearings sound like a good idea. They'd be pressed into the rockers and would get plenty of oil from the holes in the shaft directly into the needles. No need to drill the outer race. Like Jerry said, just let the oil leak out the ends of the bearings.

One thought I have is that with the rocker action, the bearings may wear grooves into the shaft (eventually) as they'd be moving in a limited range. Torrington bearings are usually designed for a rotating shaft, not oscillating motion. It may live longer than any of us in a rocker application, but it's a consideration.

Way back when, I did a needle bearing and inner race refit on a Model A water pump that was prone to wear into the shaft with the original style roller bearing supporting the fan.

We wouldn't be the first...just the first to adapt them to the Stovebolt engines. Not to get the cart too far in front of the horse but I can see there might be a chance of selling these.

https://www.jegs.com/i/Harland-Sharp/851/3002-7/10002/-1

The bearings I have en route to me have small diameter needles, spaced VERY close together, almost like a universal joint. I think shaft wear would be at a minimum, since the rollers will overlap each others' travel a little.

www.ebay.com/itm/204380274310

Jerry

You mean sort of like this? Of course, I'm just eliminating the rocker shafts altogether.

Yes! But wouldn't we need a 1.47 ratio?

I’m not sure that would work. The outer race with a slight press into the rocker would seal off any chance of oil reaching the weep hole in the top of the rocker. It’s my understanding that the weep holes are what supply oil to lubricate the both the top of the valve stems and the push rods. In addition, the pressure loss from the open ends of the bearing may be to much to allow oil to reach the weep hole, even with holes drilled in the outer bearing race. It’s possible the oil weeping out between the rockers and spacers, might carry enough oil to lubricate, but I have my reservations.

Just thinking of some possible issues.

Some people make things happen. Others watch things happen. Most people ask "What happened?" Henry Ford, Walter Chrysler, Harley Earl, Charles Kettering, Samuel Colt, and John Moses Browning were in category #1. If they hadn't chosen the path they did, we'd still be riding horses, and hunting with stone-tipped spears, and the vast majority of the world would be happy with the status quo!
Jerry

I thought we were brainstorming here. I’m not trying to discourage you from developing new ideas, just identifying potential pitfalls.

The 700+ HP MOPAR 440 truck pull engines I built for several years back in the late 1990s used needle bearing roller rocker arms on OEM shafts that ran the full length of the cylinder heads, with triple valve springs and a roller cam. Seat pressure on the valves was in the 300+ pound range and we ran them 7K+ RPM. Those roller rockers used simple close-fitting flat washers at each end of the roller bearing to retain the oil. I don't recall having any oiling problems or shaft failures.
Jerry

One step forward- - - -two steps back! I set up a worn rocker shaft in the lathe, and did a little whittling on it with some mixed results. First- - - - -those shafts are HARD- - -but only where the rocker arms run. The space in between rockers is considerably softer. The hard areas are also deep- - - -no need to worry about cutting through into softer metal. It looks like machining a shaft down to 3/4" diameter will take care of even deeply worn areas, which is about a .040" (1MM) reduction in diameter. Shouldn't affect the rigidity of the shafts at all. The original diameter is around 0.790". 3/4" (0.750) ID Torrington bearings are plentiful, and fairly inexpensive. Of course, if the idea of fitting Torrington bearings to the rocker arms doesn't appeal to you, installing thin wall bronze bushings in the rocker arms to fit the reduced size shafts would be a simpler, and much less expensive option.

Downside- - - -unless a follower rest is used, the shaft will flex and make it difficult to maintain a uniform diameter from end to end while machining. That's particularly true since you'll be making an interrupted cut across a lot of holes, and dealing with different hardnesses of metal along the way. A tool post grinder will probably be the right way to go to get a uniform diameter and finish from end to end. Obviously, thin bushings will need to be installed in the support stands to adapt to the slight reduction in shaft diameter. Fun project!
Jerry

Back to the original project- - - -flipping the shafts over and drilling new lube holes- - - - -I'd suggest using a solid carbide drill bit in a drill press, a V block, and making press-fit brass plugs with a sliight taper to block off the original oil holes. There's not enough pressure inside the shaft to require a threaded plug.
Jerry

For “average Joe”… the guy with no access to a lathe…..just trying to make this work for less than the cost of new shaft…..I actually think the threaded plug approach might be more feasible. Easier to source, anyway.

That said, it’s amazing what McMaster Carr has available. Perhaps a tapered brass plug isn’t as hard to acquire as I imagine.

Are the shafts so hard that a special tap would be needed?

Any chance that a PTFE plug would work in lieu of the brass?

Same idea, just a different material. Start with something slightly oversize and whittle it down to make the shaft diameter correct where the rocker rides.

Sure- - - -since the pressure inside the shaft is pretty low and the rocker arm would keep it from being blown out anyway. A piece of brass rod, a drill press, and a file could be used to make a plugwith a couple of thousandths of taper to stop up the extra hole. Even a hand drill motor clamped into a vise would be sufficient. Then a High Speed Press (AKA "ball peen hammer") would be the proper installation tool. That's about as low tech as it gets!

Yes- - - -that area of the shaft is HARD! Tapping the extra hole would be risky, (tap breakage) and I don't know of anybody who makes solid carbide taps.
Jerry

Really interesting that GM chose to make the shafts so hard. Makes me think that the shaft wear comes not from low oil flow, but from complete oil starvation.

Also makes me wonder just how hard the rockers are, since the shaft seems to wear before they do.

The rockers I've measured are a little bit egg shaped, but it seems that they don't wear nearly as much as the shafts. I've seen the same kind of problems elsewhere- - - -a soft surface running against a hard one, and the hardened area gets most of the wear for some reason. I think you're on the right track with the "oil starvation" idea. Cast iron with a high nickel content in the alloy seems to be very wear-resistant. Look at the wear on an engine's cylinders between different makes- - - -Chevy (and GM engines in general) got much more cylinder wear than Ford back in the 1950s. Ford put a lot of nickel in their cast iron alloys, and Hudson engines with the very high nickel content in their blocks could get two or three re-ring jobs before needing to be rebored.
Jerry