Valve Seat Material

While I was doing a bit of research on cylinder heads, I stumbled upon a very interesting piece of information on AA1Car website on valve seats. This is truly one of the best automotive engineering websites in the world. It is rich in technical information and one of the key authors of this information is the one and only Larry Carley.

Here are links to his thoughts on valves and seats:

http://www.aa1car.com/library/2003/eb40332.htm

http://www.aa1car.com/library/ar993.htm

In one of his articles he explains the reason why valve seats fall out. While explaining the reason they fall out he made mention of the valve seat material.

What got my attention was the statement that cast iron valve seats are not the most suitable for making valve seat inserts. This came as a bit of a shock to me because I have been machining and installing cast iron valve seat inserts on passenger vehicles for a long time. On heavy vehicles I machined steel alloy valve seat inserts.

So I immediately wrote a rather disturbed letter Mr. Larry Carley Seeking clarification on this matter. I explained to him that the specific type of cast iron was a 'G' grade close grain cast-iron, also known by the trade name 'Mehenite'. One why to identify it is that there are no blow holes on it.

I his reply he confirmed my fears and he went on to explain that ordinary cast iron valve seats are not the best choice for today's engines. They may be okay for light duty intake valves, but they do not hold up well for exhaust valves or in engines that run at high temperatures or work hard. One exception he mentioned is performance heads with titanium valves. This information was collaborated by several automotive engineers.
Now this got me thinking: what is the fate of all those cylinder heads that we fitted with cast iron exhaust seats? How significant is this wear?

We did machine work for a number of commercial transporters on their cylinder heads (for their passenger vehicles) All our work carried a guarantee on workmanship and spares supplied yet I do not recall a job being returned for premature valve seat failure.

I may have missed it because worn valve seats were not the primary reason the head was brought in and reconditioning the seats was merely incidental.

I am starting to think that these highly esteemed gentleman where assuming that I am talking about the common low grade cast iron. All the same, to my fellow engineers out there, avoid using cast iron seats because of the metallurgical data against it.

I am working on finding the most suitable material that can be used to machine valve seats in Africa. There are some aftermarket inserts that are on offer but these are not cost effective for Africa –it would make more sense to stick to a high grade cast iron.

Does anyone out there know a suitable cost effective alternative to cast iron?