FE iron head guide issues?

[GerryP]

What do they make to add to the gas to take the place of lead the old tractor guys add something to save the seats

Older gasoline tractor engines generally don't make a lot of heat even when working so they are pretty easy on valve seats.  The valve seat erosion is the result of a phenomenon called microwelding.  At high metals temperatures, very tiny bits of cast iron head seat material attach to the valve.  It's molecular, but it has the same affect as death by 1,000 cuts.  Some engines by design, like flatheads, make so little combustion heat they have very generous octane requirements and can run on a variety of fuels without consequence.

[Barry_R]

I have had a couple occasions where we experienced guide issues on iron heads.  Might not apply to the original question, but worth noting.

First is that I have seen some valves that had obvious issues with the stem plating.  Most valves will use a flash chrome plate on the stems for wear resistance.  Chrome is really hard and can be pretty abrasive if it's not glass smooth.  I've see a few where there was almost a gritty or bumpy finish.  I've run a bit of 600 wet or dry & WD40 on those with the valve in a drill to smooth them out.  At one time somebody sold a little grinding fixture to put a cross hatch on stems for high end race stuff.

I ran into an issue where we were sticking exhaust valves on the dyno during power runs.  Often the valve would release once the engine cooled down.  Using full bronze replacement guides.  Ended up fixing it by opening up clearances a little and cutting back the portion of the guide that extends into the port a good bit.  I think the bronze and iron had different expansion rates and the guide would tighten up on power runs as exhaust temperatures increased.  I'm sure that the guide would have worn prematurely in a less aggressive environment as it "dragged" when hot rather than fully sticking. 

Lesson is that surfaces need to be smooth and straight, and we don't need guide clearances to be super tight "just because we can".

[pbf777]

  I've run a bit of 600 wet or dry & WD40 on those with the valve in a drill to smooth them out.  At one time somebody sold a little grinding fixture to put a cross hatch on stems for high end race stuff.

     When deemed necessary I will chuck the valve in the lathe, spin it fast and apply an appropriate grit W/D paper with cutting oil with a floating flat back-up 'shoe' to polish the stems.   

     Scott.