Valve - valve guide material compatibility

[Duke W.]

It's been reported to me that David Vizard, in one of his books, states that stainless steel valves require bronze valve guides. I was not aware of this and would like to hear from others whether there is an industry consensus on this subject.

The AMA specs for my Cosworth Vega state that the OE exhaust valves are 21-2N (21 percent chromium, 2 percent nickel) stainless steel, and the OE valveguides were definitely cast iron inserts (aluminum head, current guides are nickel-bronze).

I find it tough to believe that GM would use incompatible materials, which is why I'm interested in hearing more about this subject.

Duke

[Michael H.]

Re: Valve - valve guide material compatibility

Duke,

I agree, that doesn't exactly sound right. Weren't many of the big block exhaust valve stems hard chromed and run in iron guides? I'll have to look into this later.

[Clem Z.]

hard chrome is the answer as all chevy HiPo

valves had hard chrome plating.titanium valves even coated stem ones need phos bronze. cast iron and non plated valve stems are both "soft" metal which could cause sticking and or rapid wear under certain conditions.

[Scott Marzahl]

Re: hard chrome is the answer as all chevy HiPo

Yes, all the high quality Stainless Steel valves like Manley and Ferera are hard chromed, which is not the case for the cheap offshore made valves that are also not polished very well. They typically have a very rough RMA finish.

[Mark #28455]

stock late model BB has stainless valves

The stock late model BB valves from about the late eighties on are all stainless steel. They did NOT use a special bronze valve giude - just the iron type.

Mark

[Michael H.]

Re: Valve - valve guide material compatibility

Duke,

I was interested in this so I decided to look deeper to see what GM had to say. So far, I've learned that for the 66 model year, there was only one engine that used valves with "chrome flash" stems. That was the L72. No mention of this for any other small or big block.

The material is shown as "alloy steel" for intake and "high alloy steel" for exhaust for all engines. I don't know what the "alloy" is though. I'll try to find out.

[Duke W.]

Re: hard chrome is the answer as all chevy HiPo

What about OE valves and integral guides? I don't think the OE valve stems were plated. I'm talking road engine, not racing engine.

Duke

[Duke W.]

Re: Valve - valve guide material compatibility

GM is not very specific about "alloy steels", but I assume they are less than stainless, and IIRC the lowest grade stainless valve steel is 21-2N with 21-4N being an upgrade. Beyond that you get into inconels.

My Speed Pro catalog lists "8440" alloy steel as a material for some inlet valves. Most have chomed stems, but I don't know the analysis of that alloy. I think it's a "trade name" alloy, not a SAE or other standard alloy. It's not stainless, but I don't consider stainless to be necessary for a road engine inlet valve. Stainless is a good idea for exhaust valves since they can reach well over 1000F in sustained hard running.

Some of the Speed Pro 21-2N and 21-4N have chromed stems, some don't.

Here's a rundown on the Speed Pro valve steels.

1541: Carbon steel with added managanese for improved corrosion resistance.

8440: Medium to heavy duty steel alloy with higher chomium content than 3140 to enhance high temperature strength.

Sil 1: Heavy duty alloy steel with 8.5% chromium content for excellent high temperature performance. Used for most high performance intake valves.

Ti-6: Titanium - 40 percent lighter than steel, used for racing applications [probably way overkill for any street engine that is not intended to rev much above 7000]

21-2N Austenitic stainless steel 21% chromium and 2% nickel. As the most popular exhaust valve material, it has excellent performance characteristics at elevated temperature.

21-4N: Austenitic stainless steel similar to 21-2N, except for a greater nickel content (4%), used as a heavy duty alternative to 21-2N

Unfortunately, they say nothing about recommended guide material for the various valve materials or stem treatments.

Duke

[Mark #28455]

exhaust valves, sorry *NM*

[Clem Z.]

Re: Valve - valve guide material compatibility

stainless steel is a "soft" steel compared to other steel that can be heat treated to difference hardness. i have never seen a stainless steel valve that did not have a hard chrome stem but i have only worked with high performance valves.

[Michael H.]

Re: Valve - valve guide material compatibility

Clem,

If I remember correctly, stainless steel is, basically, steel that has anywhere from 10% to 20% chrome added to the mix. There is no such single element as stainless steel. The addition of chrome makes it an alloy. I wonder if it's still necessary to chrome coat the stems if a high percentage of chrome is in the alloy. I thought stainless was harder than steel?

I'm going to do a little research on stainless steel.

[Michael H.]

Re: Valve - valve guide material compatibility

Thanks duke. This is a lot more involved than I originally thought. I suppose it's not surprising that there are so many different materials used for valves, especially for competition engines.

We never bothered to look into the making or lineage of valves years ago. We just used GM or aftermarket titanium. (GM sold titanium exhaust valves in the early 70's but they were nearly $90. each, as I remember)

Tried the fancy titanium 5/16" stem Manley valves a few times but I don't think anything good ever came of it. Waste of money as far as I'm concerned.

[Jeff S.]

Re: Valve - valve guide material compatibility

Michael

If iron is alloyed with a minimum of 11% Cr, a protective oxide forms that is self-healing & resistant to corrosion; 'stainless' properties are achieved. The lowest grade "entry level" stainless is 11Cr (Type 409) common in sheet metal products such as catalytic converters. Often called 'muffler steel', it is magnetic, not particularly strong, useful to ~1050F, moderately difficult to weld, and does not respond to hardening by heat treatment.

The Cr-Ni (or Cr-Ni-Mn) stainless family is austenitic & non-magnetic. Common chemisties are 18Cr-8Ni or 18Cr & [Ni+Mn]>8. Better high temperature properties & toughness than the straight chrome grades. Not particularly strong, do not respond to hardening by heat treatment & are difficult to machine -- often galling (cold welding) when used in high friction applications against materials of similar hardness. Exhaust valves like 21-2N or 21-4N are in this family. The Cr in the maxtrix (21%) does not contribute to surface hardness. It is necessary to electroplate a barrier of 'hard chrome' (perhaps .0005"). This both reduces the cooficient of friction & increases surface hardness.

[Michael H.]

Re: Valve - valve guide material compatibility

Thanks Jeff. So, as the chrome content percentage increases, so does the requirement for surface chrome in the case of an exhaust valve? That's interesting. I would have guessed it to be the reverse of that.

What effect would this have on/in a bronze valve guide? Would this be the reason GM chose to flash chrome the stem instead of use a bronze guide? Much cheaper and more dependable to flash chrome I suppose.

[Clem Z.]

Re: Valve - valve guide material compatibility

SS is "gummy" and if you use SS bolts into SS you had better use never sieze if you want to get them back out as they will fuse together..