Cast Iron for Piston Rings

[gmac]

I have a few questions regarding the selection of grades of cast iron used for IC engine piston rings - before I order some material stock.

Although the engine plans I've seen state cast iron; none specify the grade of cast iron - other than some saying close grain centrifugally cast. I may have located a supplier locally that stocks the following;

A48 Class 40 Gray Iron
65-45-12 Ductile Iron
80-55-06 Ductile Iron

Which of these is preferable for piston rings? Why? (Bearing in mind my intent is to use the George S. Trimble method of fabrication / heat treatment.)

How much oversized should stock be to allow for the removal of any outer skin - when speaking of 3/4" or 1.0" nominal dia. rings?

All comments welcome. Thanks.

Garry

 

[TinkerJohn]

Garry,

For what it’s worth, I’ve made rings before for the Upshure engines.

I got a hold of a few wheel cylinders made of some of the best turning cast iron. It was not difficult to find them in the ~one-inch sizes. I went to some brake shops and got all I could use. You may consider those, especially for practice.

In reality, I found the mystic surrounding making the rings much more profound that actually making them; when I got around to making them it took less than an hour, start to finish, including heat-treating.

You may already have the info in the link below. It talks about ‘centrifugally cast iron’. I’m not sure what that means.

Here’s the link: http://www.jerry-howell.com/PistonRings.html

Also “The Shop Wisdom of Phillip Duclos” (Village Press Books) has some really good info and pictures. That’s the source I used when making rings.

Good Luck

---TinkerJohn---

 

[rklopp]

You may want to stay away from the ductile grades, due to difficulties with making a sharp cleave when splitting the rings. As far as skin, usually continuous-cast iron bar, whether ductile or gray, is sold oversized to clean up to the claimed nominal size. Thus, if making a ring to finish to 0.75", buy 3/4" nominal bar. Obviously you can make smaller rings from bigger bar, but not vice versa ;D .

 

[ghart3]

Agree with Rklopp, stay away from the ductile grades. Had made some rings from ductile cast iron and they were way too soft. They would bend easily and not return to shape. Could almost make a figure 8 out of them. Good iron but not good for piston rings.

 

[gmac]

Thanks for the input guys....

TinkerJohn: I'm currently working on the Upshur Twin, intending to do it with O-rings but wish to fab a second piston with cast iron rings as my first go at cast iron rings. I'll make a trip to the brake shops for stock!

rklopp & ghart3: thanks for the comments on splitting the rings and softness. I always thought of cast irons (all) to be brittle - wouldn't have imagined they could be deformed that much.

Looks like it will be junk yard materials or Class 40 Gray Iron for the first engines.

Cheers
Garry