Cam/Valve bucket material and treatment

I don't have specialist knowledge - but making cams, buckets. followers etc. of nitrided 4140 is as good as any a method. A lot of the odd materials and manufacturing methods used by the car makers is to save money. Although not expensive for "one-offs" etc. - it is expensive if you are making millions of cams etc.

Cosworth use 2 series for bucket carriers...others use 7 series...I have used 2, 6, and 7 for same with no trouble...race/road, many miles on all - no issues. (running direct on raw aluminium)

I have made cams and lash caps before from nitrided EN40B many times also...again, no issues.

As for buckets, you would be mad to make - theres literally 1 million types to pick from.

B.

Thanks for the replies.

Can I use the same material and hardness on both cam and bucket? Should really have 1 harder than the other I would assume but does that need to happen with Nitriding?

BrianGar said:

As for buckets, you would be mad to make - theres literally 1 million types to pick from.

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Ideally yes but I am having trouble finding some. I need 44mm diameter.

The application is converting an old rocker style to bucket. So I am limited by the original envelope which leads me to a non standard bucket.

If I could find a 44mm OD bucket I could make it work with custom lash caps.

Image below shows the bucket with a large standoff (thats where the original rocker use to be)

When using different materials you can influence which component will wear first. Usually the most expensive component is made from more slow wearing material. Thus I would prefer more hardness of the cams then the buckets. Using different material has a additional advantage - it will prevent adhesive wear because the materials do not so easily "stick" to each other. I wonder however whether the use of Al buckets is a good idea. Due tot the "hammering" of the cams on the buckets that might lead to problems with the buckets and the need for early replacement. Two different kinds of steel might be your best bet, in combination with engine oil with sufficient anti-wear additive and sufficient HTHS viscosity.

If you are planning to use shim-adjustment you could put the shim on the cam side of the bucket (eg 2 valve Fiat). That would also allow you to make the bucket from softer, lighter material.

je suis charlie

Is it really wise to copy anything done by Fiat?

Lots of the old school air-cooled Japanese motorcycle engines did it that way, too. The shim was on top of the bucket and was the contact surface to the camshaft. Nowhere near the diameter you are looking for, though.

Twin cam hemi-head and SOHC Fiats were produced in the millions over many years. Reliability of the valve gear was excellent. What if I said Toyota or Kawasaki?

40mm flat shims from 3mm - 5mm are readily available from places like this Link

je suis charlie

romke said:

I wonder however whether the use of Al buckets is a good idea. Due tot the "hammering" of the cams on the buckets..

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By Al do you mean aluminium? I plan to use aluminium for the boxes that the cam and bucket run in. Plan for steel for both cam and bucket. The question is what steel.

It looks like nitrided EN40B is common for high quality cams. Also 8620, 5160, 5150.

gruntguru said:

40mm flat shims from 3mm - 5mm are readily available from places like this Link

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Thanks for that. Shim on bucket is definitely an option if I can understand what the detail or tolerance is for retaining them.
Any idea what buckets the 40mm shims go in?

Im possibly larger than I need to be on the 44mm bucket OD.
The springs its going over is 38mm. I could probably get away with 41-42mm OD

Got any leads on large buckets?

I think the Fiat engine that you are looking for parts from, is the FIRE 1.2 8-valve. It's possible that other versions of the 8-valve FIRE engine (1.0, 1.1) also used the same parts.

The FIRE 8-valve engine was solid in huge quantities for a couple of decades - just not in North America.

See here.

Or the earlier Lampredi designed 2 valve hemi. Link

je suis charlie

not-a-number said:

Thanks for that. Shim on bucket is definitely an option if I can understand what the detail or tolerance is for retaining them.

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That part is relatively easy- shrink your bucket height as shown by whatever you want your mean shim thickness to be, put the shim above the bucket in the existing bore in your 'cam box', and let the cam hold the shim in place. As long as the shim is captured fully by the bore of the cam box, when the valves/springs/cams are installed the shim has nowhere to go.

This link shows the procedure for removing shims on a BMW S14 cylinder head (from the 1st generation BMW M3) but as you can see, nothing holds the shims in place except the bore in which they live, and valve spring pressure. No other parts are required.

I have never see a shim with the same OD as the bucket. They are always counter-bored into the bucket - including the BMW pictures in the link.

je suis charlie

Yes, the bucket takes all the sliding side loading in the bore, the shim is much too short for that. I've heard of shims being spit out in extreme over rev valve float conditions which is why most of the modern designs put the shim under the bucket. But that makes adjustment much more difficult as you have to remove the cam.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

Why are you actually doing this? The modern trend is to use a finger follower or pivoted follower of some sort - like F1.

So the original assembly has a finger follower. Thats a good solution but the cambox is a complicated casting. They are also about 800mm long so the oil feed tube (also the pivot for the rockers) is extremely long and not easy for me to machine.



Im restricted to having the cam and valve position fixed. So I have to work around that.
Initially I thought an easy solution would be to just machine some bores in a billet and put big OEM buckets in there.



Maybe I could do a roller rocker and roller lobe follower so I dont need to worry about material hardness.

I didnt realise F1 engines (or engines in general) did 1:1 followers like this. They also seem to be an individual assembly that bolts in which would be good for machining.

Ill investigate more

Doesn't look like you have room for rollers without raising the cam a bit.

je suis charlie

Though it's common to select a softer grade for the lower cost component, I wouldn't go all the way down to aluminum driven by nitrided steel. If I were making custom parts to mate with an off-the-shelf cam, I would actually strive to make the custom part harder because it's going to be more costly to replace.

Per Newman Cams (and as noted by BrianGar above), the best steel for cam shafts is EN40B aka 722M24 aka 31CrMo12(1.8515). This steel has a hardness spec of 276-339 HB which is 29-36 HRC. I can't find any suppliers of small quantities, so you might want to consider a more readily available alternate.

You can buy one of the hardest steels made, [link en.wikipedia.org/wiki/Maraging_steel]Maraging 350[/url], from onlinemetals.com. It machines like 4340 in the annealed state but attains hardness of 58 HRC (!) once heat treated and aged. It also has superior toughness, and doesn't significantly change dimensions during heat treatment and aging. It's costly, but you don't need much, and you could always switch to the cheaper 31CrMo12(1.8515) if you ever want to built in quantity.

H-13 Tool Steel has hardness of up to 53 HRC and is available from onlinemetals.com for about half the cost of Maraging 350, but it's much more difficult to machine than Maraging 350. Its bulk cost advantage will be offset by its machining cost to some extent.

As for Formula One valve train design, you might find Honda's paper [link f1-forecast.com/pdf/F1-Files/Honda/F1-SP2_09e.pdf]"Development of a Valvetrain for Formula One Engine"[/url] useful.

RodRico said:

Though it's common to select a softer grade for the lower cost component, I wouldn't go all the way down to aluminum driven by nitrided steel. If I were making custom parts to mate with an off-the-shelf cam, I would actually strive to make the custom part harder because it's going to be more costly to replace.

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Thanks for the information RodRico. I definitely dont plan to use nitrided Aluminium for any of the cam parts.
The cams will also be custom so can be made of my choosing. I would pick the cam to be the hardest material because of this.

The thing I am restricted to is the position of the cam and valve.

I am having a bit of trouble fitting a finger follower without doing more complicated machining on the cam box.

So my options could be:
Cam - Maraging 350 @ 58 HRC
Follower - H-13 @ 53 HRC

or

Cam - EN40B (nitride to 61+ HRC)
Follower - Maraging 350 @ 58)


If anyone is interested, this is my project. I have a long way to go but I am at the stage of needing to spec materials and tolerances.