Cam/Valve bucket material and treatment

[not-a-number]

Im building an engine and require custom valve buckets. (Cam running directly on top of the bucket)

Couple of questions:

What material and harness is normally used for a bucket?

They are going to run in a billet machined cam box. What is a good Aluminium for cams and followers to run directly in without bearings or sleeves?

 

[RodRico]

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.

Wow! That's one heck of a project you have going there! Fascinating. I admire your fortitude and skill.

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

Did the Bugatti use a finger follower? From this article about the Kawasaki Ninja engine, it sounds like the primary purpose of the finger follower is to reduce mass in high revving engines, and I doubt an old Buggatti fits that definition. At the very bottom of the article they note that finger followers wear faster and they abandoned them for a while as a result. They only use them now because modern materials (DLC, an extremely hard coating) solve the wear problem.

So my options could be:

Another option for you.... There are multiple grades of maraging steels and three (250, 300, 350) are available online. The hardness of these grades is 50, 54, and 58 HRC respectively. Using 350 for the cam and 300 for the follower would do the trick, and would keep you from having to mess with hard to work tool steels like H-13.

 

[not-a-number]

Did the Bugatti use a finger follower?

Yes the original (for this particular engine) used a finger follower. Image below

There are a few issue with it that has lead me to try and modernise/simplify it.

#1 The cam box is a thin complex casting.
#2 The pivot point for the fingers is an oil shaft that runs the entire length of the box (700+mm long)
#3 The oil pivot shaft feeds the cam bearings and also the fingers
#4 The fingers have a crossdrilled hole to lube the cam lobe. But its not continuous, the holes line up at a particular point so that you keep good oil pressure.

Hope that makes sense. So my thinking was that I run oil down the center of the cam. I run a billet machined cam box that I can use good material for and simple bucket followers.

it sounds like the primary purpose of the finger follower is to reduce mass in high revving engines, and I doubt an old Buggatti fits that definition.

Yes thats my understanding. They only rev to 5000ish rpm. They had wear issues (though that could be solved now)

Using 350 for the cam and 300 for the follower would do the trick

Excellent. Thanks for the information. That looks like the way to go.

 

[SwinnyGG]

If you run oil down the cam, you have the same problem with regard to drilling a deep hole.

The shaft you need to provide oil to the followers is something you can very easily buy. Hollow shaft stock is readily available and cheap; you'd just need to drill radial holes and grind grooves at each pivot location.

 

[not-a-number]

If you run oil down the cam, you have the same problem with regard to drilling a deep hole.

Yes but the difference is it is common practice for a camshaft to have an internal oil gallery feeding the bearings. Can gun drill this no problem because the accuracy and tolerance isnt critical.

The shaft you need to provide oil to the followers is something you can very easily buy. Hollow shaft stock is readily available and cheap;

You are right, I could buy hollow shaft pre ground or grind it myself. Thats not the difficult part.
The difficult part is the accurate tight tolerance hole I need to drill down the entire length of the cam box. The hole for this oil tube to be installed in.

 

[SwinnyGG]

The hole for this oil tube to be installed in.

I guess I'm missing the point.. You're already going to have to drill a very precisely located and sized deep hole which will then have to be highly polished, to serve as a bearing surface for your cams.

Drilling this long hole with enough precision to locate a very low-speed (ideally zero speed) shaft is not terribly difficult for a competent machinist. The shaft that mounts your finger followers could be held in place by caps as well.

 

[BrianPetersen]

I'm thinking the best choice is to preserve the original design and layout but construct replacement parts using modern materials, and perhaps fix any known deficiencies in the design.