Valve Construction

[Shel_B]

I have heard comments about, and seen images of, two piece valves, where the head and the stem are joined together, as in this image:

I have heard of valves breaking apart where they are joined together, although it seems to be a rare occurrence. It seems to me that the area where the two pieces are joined might be a failure point, and that a one piece valve might be stronger, but I don't know that such is actually the case.

Why are valves made in two pieces? What's the benefit of such construction? Would a one piece valve be inherently stronger?

 

[Jetronic]

I have heard comments about, and seen images of, two piece valves, where the head and the stem are joined together, as in this image:

View attachment 249948

I have heard of valves breaking apart where they are joined together, although it seems to be a rare occurrence. It seems to me that the area where the two pieces are joined might be a failure point, and that a one piece valve might be stronger, but I don't know that such is actually the case.

Why are valves made in two pieces? What's the benefit of such construction? Would a one piece valve be inherently stronger?

Are those sodium filled valves? They'd be hollow and partly filled with sodium to transfer heat away from the valve head.

 

[wwillson]

From what I've read about exhaust valve construction is the heads are made from metal alloys that can handle very high heat, but are often very heavy. The stem is made from a metal alloy that is lighter and conducts heat better. The best of both worlds.

 

[Exhaustgases]

In manufacturing its about cost, can't be wittling tooth picks from big logs.
A correctly sized round stock could be heated and upset to have the enlarged head area and then all machined.
They are going to use the least expensive process they can find.

 

[Shel_B]

Are those sodium filled valves? They'd be hollow and partly filled with sodium to transfer heat away from the valve head.

I don't know. It's just a pic that I grabbed to show the two part construction.

 

[Shel_B]

From what I've read about exhaust valve construction is the heads are made from metal alloys that can handle very high heat, but are often very heavy. The stem is made from a metal alloy that is lighter and conducts heat better. The best of both worlds.

Thanks for your input.

 

[Exhaustgases]

Not saying they are not welded. But sorry there is nothing in the picture that proves they are. That is just the normal scale or darkened area from heat treat that has not been machined, fresh out of a heat treat oven the whole valve would look that color. Every other area that is not dark has been machined, grinding is a machining operation.
Even the grooves for the locks/keepers are the dark color.
The area where the stem is ground to the darker area and has a radius step is from the grinding wheel.

Here is a video that should help show what I've been talking about, and it shows something I was going to mention about just welding hard material to the seat area, that has been done since I think before the WW2 times, especially for aircraft.

 

[wwillson]

Not saying they are not welded. But sorry there is nothing in the picture that proves they are.

At :30 seconds you can see they are stir welding what appears to be the stem to the head

 

[Exhaustgases]

At :30 seconds you can see they are stir welding what appears to be the stem to the head

Sure they show all the tricks. They show the upset deal I mentioned. Welding hard face to the valve faces etc etc.
And sure some valves are welded like you say. But the photo did not prove that is what was done to the ones in the picture.