Metallurgy question Rajo rocker arm shaft.

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dobro1956
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Metallurgy question Rajo rocker arm shaft.

Post by dobro1956 » Sat Jan 04, 2020 11:01 am

Im getting ready to do the final rocker arm assembly of the Rajo 4 valve head on the speedster project. Im changing the two separate rocker arm shafts to a single shaft. My rockers are solid castings with no bushings.

I have several choices of 5/8 inch shaft material from McMaster Carr. I am leaning toward 4140 or stainless steel, but thought I would see what some of our more knowledgeable metallurgist folks think.

Also if someone knows of other suppliers or materials for a 5/8 x 36 inch shaft, please let me know.


Below, is what McMaster Carr says about their shafts, all their shafts have a tolerance of (minus) -.001 to .000 that should give my rockers an aprox. running fit of .001

Combine these general purpose drive shafts with gears, sprockets, and bearings to transmit rotary motion. All are turned, ground, and polished to meet tight diameter and straightness tolerances.

Steel shafts are generally stronger than stainless steel shafts but not as corrosion resistant. 1566 carbon steel shafts balance high strength and good machinability, making them ideal for general purpose use. 12L14 carbon steel shafts have a lead additive that makes them easier to machine than any other rotary shaft but also more prone to wear. Black-oxide 1045 carbon steel shafts have a black-oxide coating for mild corrosion resistance. Chrome-plated 1045 carbon steel shafts have a 0.0001"-0.0005" thick layer of chrome plating on the outside of the shaft that provides wear resistance and some corrosion resistance. Nitride-coated 1045 carbon steel are the most corrosion resistant steel shafts. 4140 alloy steel shafts are for high-load applications. They have the highest yield strength of any steel shaft; however, they are more difficult to machine than carbon steel shafts.

Stainless steel shafts are more corrosion resistant than steel shafts but also more difficult to machine. 303 stainless steel shafts have good corrosion resistance. 316 stainless steel shafts have excellent corrosion resistance.

Shafts with chamfered edges have their edges ground to reduce damage to bearings, housings, and other components during installation.


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Re: Metallurgy question Rajo rocker arm shaft.

Post by Scott_Conger » Sat Jan 04, 2020 11:20 am

Your gut feel for shafts is pretty good. 12L14 is out of the question, and I think it would be a mistake to not bush the rockers with an appropriate material.
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Mark Gregush
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Re: Metallurgy question Rajo rocker arm shaft.

Post by Mark Gregush » Sat Jan 04, 2020 11:33 am

What about drill rod? While my experience machining it was not that great with the tools I had. If all you are going to do is drill holes for retainers or cut grooves for clips it should work fine and comes in a range of sizes.
Here is a sample;
https://toolsteelservice.com/product/to ... drill-rod/
What if you went to a smaller diameter and added bushings to the rockers. You would then have to add bushings of some sort at the towers to make up the difference in diameter. Maybe the bushings at the towers could be split for ease of installation.
I know the voices aren't real but damn they have some good ideas! :shock:

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Re: Metallurgy question Rajo rocker arm shaft.

Post by Scott_Conger » Sat Jan 04, 2020 11:50 am

Donnie

I'm not a speed guy and thus know little of the head you're using. Lack of knowledge leads me to ask: why are you altering the original design and going to one shaft?
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Re: Metallurgy question Rajo rocker arm shaft.

Post by Dropacent » Sat Jan 04, 2020 12:53 pm

Going from memory, which is always dangerous, but I think Donnie has a 4 valve rajo head. I’ve seen a couple , including mine , that had a repair to the original stand. It was designed pretty light, and not a lot of room for bushings originally. I think the idea of a single shaft is a good one, and will add some strength to the setup. The original 4 valve had an open backed valve cover, and as one of the selling points was no modifications were needed to the original firewall to install. Somewhere in time, a pair of RAJO marked valve covers were made, and about 20 years ago I made foundry patterns for the double valve cover design. I sold a couple dozen sets, but probably been about 10 years since I’ve had any. Of course, the single shaft wouldn’t work with the double covers.i believe the double valve covers were and are a fantasy item.
If I did it again, I’d probably make billet towers beefier than original, large enough to bush properly, have some easy to oil spots, or small oil cups on the shaft, and make ( or find an original) open backed valve cover. Maybe even use without a valve cover, as I’d say it would be pretty neat to see that valve action.
I said a lot without saying anything about metallurgy, as I think anything modern ( except stainless steel) would be better than Joe used originally.


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Re: Metallurgy question Rajo rocker arm shaft.

Post by Scott_Conger » Sat Jan 04, 2020 1:33 pm

Tim

thanks for the education. Plus, I read back to the original post and I missed the part about stainless. I agree that this would not be the best choice. Glad you caught that.
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Re: Metallurgy question Rajo rocker arm shaft.

Post by Jerry VanOoteghem » Sat Jan 04, 2020 6:03 pm

Drill rod, as previously mentioned, should be ok. I would also think of Thomson Shafting. It has a very hard outer shell, (Rc 60/65 case), for wear resistance, and a softer interior hardness, for excellent toughness. Don't know what machining you'll need to do however, so the very hard case might be a problem for you. As others have stated, I'd find a way to use bushings in those rockers.

https://www.mscdirect.com/product/details/35522275

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Re: Metallurgy question Rajo rocker arm shaft.

Post by dobro1956 » Sat Jan 04, 2020 7:23 pm

Yes, it is a Rajo 4 valve. I believe original heads had a single shaft. The repro heads had 2 separate shafts and the rocker towers are taller. I believe the towers of the repro heads were made taller to accommodate a pair of off the shelf rockers. It is rumored the rockers are Chrysler, but I have not yet found out what the repro rockers are from. The taller towers make the stock long valve cover not fit anymore . So the repro heads came with a pair of seperate rocker covers. But. the two single rocker shafts brought to the surface a design problem. The position of the two bolts that bolt down the rocker towers allow the rocker towers to "rock" front to rear till the bolts or towers fail. It was one of the major complaints of the repro heads. By converting the two rocker shafts back to original style single shaft. The problem goes away. Since the repro rocker parts will bolt to an original head, there is the possibility of mixed original parts to show up today. I suspect that my head is original with repro rocker parts and covers ????

Seth from Alabama was running a 4 valve head with 2 single rocker shafts, and said he could see the rocker towers moving. He installed a single shaft and fixed the problem. Seth used a stainless shaft, and I believe it worked out well. But I feel like stainless may not last as long and be harder on the rockers.

The original rockers I have seen did not have bushings. I believe my rockers should be OK with the limited mileage it probably will receive.

Ill check into the Thompson shifting , right now I'm leaning toward the 4140

Thanks for the input


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Re: Metallurgy question Rajo rocker arm shaft.

Post by Erik Barrett » Sat Jan 04, 2020 7:26 pm

My original Rajo four valve had separate shafts which damaged the head. It’s a bad design. I went to a single stainless shaft with great results.


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Re: Metallurgy question Rajo rocker arm shaft.

Post by Dropacent » Sat Jan 04, 2020 7:55 pm

Mine was original also, Donnie, with two separate shafts. I don’t recall any issue with anything rocking, but do recall the upper part of the tower wasn’t as beefy as I would have liked. I’m remembering an old forge weld repair where someone before me thickened it up nicely. I have no experience with and have never seen a reproduction , so cannot speak to that at all. At some point I think I was told the reproductions were aluminum castings, but not 100% sure if that is a fact. My 4 valve head went to a customer of Engine Joe Bell, and was happily running last time I heard. I would think when you start making things and changing the geometry to use off the shelf modern stuff, you likely could run into trouble.
I like the sound of the shafting Jerry mentioned, and that’s why I have different size carbide drills in the drawer, to get through the skin. I’d be tempted to try that. About 4 cotter key holes and you’d be good to go.

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Re: Metallurgy question Rajo rocker arm shaft.

Post by dobro1956 » Sat Jan 04, 2020 8:03 pm

For those not familiar with Rajo 4 valve heads, here are a few pics of my head (red) when I had it mocked up in the speedster project. The black heads are other heads I found pics of on the web.
zzzzzzzzzzzzzzzzzzzzzzzzzzzz (1).JPG
zzzzzzzzzzzzzzzzzzzzzzzzzzzz (2).JPG
zzzzzzzzzzzzzzzzzzzzzzzzzzzz (5).JPG
zzzzzzzzzzzzzzzzzzzzzzzzzzzz (6).JPG

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Re: Metallurgy question Rajo rocker arm shaft.

Post by dobro1956 » Sat Jan 04, 2020 8:04 pm

zzzzzzzzzzzzzzzzzzzzzzzzzzzz (3).jpg
zzzzzzzzzzzzzzzzzzzzzzzzzzzz (4).JPG


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Re: Metallurgy question Rajo rocker arm shaft.

Post by Les Schubert » Sat Jan 04, 2020 8:11 pm

I will suggest 4140 ground shafting and then get it “gas nitrided” after the other machining is done. It provides about a 50 Rc hardness of a couple thou thickness. No distortion to worry about. I can get it done locally in Calgary if you can’t find a good source near you.


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Re: Metallurgy question Rajo rocker arm shaft.

Post by Dropacent » Sat Jan 04, 2020 10:22 pm

Your stands look a lot taller than I remember mine being.

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Re: Metallurgy question Rajo rocker arm shaft.

Post by dobro1956 » Sat Jan 04, 2020 11:01 pm

Dropacent (Tim) My towers being the taller towers is why I think all my rocker parts are repro. It also came with the 2 separate valve covers and the new cast aluminum intake like the Australian repros came with. All those parts are obviously new parts. As a general rule the repro heads do not have a serial number on the serial number boss at the front of the head. I thought my head was a repro till I cleaned it up. Under three different colors of very thick paint I found a serial number stamped into the boss. I can not say for sure but Im leaning toward an original head and all the rest is repro parts. ???

I have an original open back valve/rocker cover. When I install it on my rocker towers it is about 3/4 inch too short in height. Every original valve/rocker cover I have seen has wear marks on the inside where the rockers have been hitting the covers. So it appears that the original RAJO covers were made with too close of a rocker tolerance. More than likely I will run with no covers till I can make up new patterns for a new cover one inch taller than stock. I also plan on enclosing the rear of the cover. The open back is only needed if running stock coils. The open back is to clear the plug /timer wiring. Just one more of the many "to do" projects :)

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Re: Metallurgy question Rajo rocker arm shaft.

Post by George Mills » Sun Jan 05, 2020 8:42 pm

I know that there are days where I don’t fire on all cylinders…but then there are days like today when the idea keeps coming back to this like a dog gnawing on my ankle :lol:

I’ll throw this out for discussion. Why not look around for a chunk of 430 B Bronze?

Working from memory here...

Right out of the chocks 430B has a grain structure strength equal to 4140 heat treated to the mid 50's Rc (give or take just a wee bit)…

Compared to 4140 annealed…the surface and through hardness is just about equal…so any relative wear would be equal…

However…(wind ‘em up)…With manganese bronze you get the effect of a built in bushing…not for the replacement aspect…but for the built in self desire to lubricate as the bronze WILL self-lap to the maximum material condition possible from the assembly if necessary and then stop wearing as long as there is no burr.

430B has a machinability in the low 80’s so its not that difficult to machine or drill.

In fairness, I know nothing about RAJO but if the conclusion was that 4140 sounds near good enough, then I’d say look to 430B Bronze as a worthy equal before taking the next step.

Just thinking out loud.


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Re: Metallurgy question Rajo rocker arm shaft.

Post by Scott_Conger » Sun Jan 05, 2020 10:13 pm

George

I've seen you post some great metals stuff, but I'm not feeling this one. Super good bushing material, but from a design standpoint, I myself wouldn't make a shaft out of it. Now you're having to make hardened rockers and ultimately deal with a worn out shaft rather than knocking out some worn bushings and replacing them. I would prefer replacing some bushings over having to remanufacture another shaft every time clearances built up. Also have to have really good lubrication for this stuff to perform to max potential and I suspect that lubrication on this assembly is scant. All the more reason in my mind to make repairs simple.

my $0.02.

not worth much.
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Re: Metallurgy question Rajo rocker arm shaft.

Post by dobro1956 » Mon Jan 06, 2020 12:36 am

I finally got to talk to Seth about his use of stainless for his rocker shaft. The folks who remember Seth's build of his speedster engine know he is pushing the limits of a T and a Rajo 4 valve head. . After a couple years of very hard use and high speed driving, his rocker shaft shows no wear. He says the shaft has a different surface appearance but he can not measure a difference as to wear. His rockers do not have any bushings in them. and there is no oiling to the top except for hand oiling a couple times a day. The original rockers did not have bushings. As to machining the shaft, there is no machining to do on it other than drill four cotter key holes. Its pretty much buy a 5/8 shaft, cut it to length, drill four holes, and install. The shaft cost 36.00 shipping included, so that really makes the shaft a easily changed disposable item. I know that there should be bushings in the rockers, but Im trying to keep this project as basic and period correct as I can. and if they wear out Ill bush them at that time. The whole idea of this engine and speedster build is to do it as they did it then. So far my only compromise is the use of the repro rocker stands and rocker assembly. So I guess Ill take the easy road and just install an off the shelf shaft like they probably would have done back in the day.

I really appreciate all the input everyone has given ...

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