The Stovebolt Site Forums The Shop Area Engine Shop hardened valves vs. hardened valve seats

I was reading an article the other day that said when converting to unleaded, you can put in either hardened valves, or hardened valve seats, and you will be set.

This is the first I have heard about putting in hardened valves instead of seats, so I'm wondering if you guys have any thoughts on this, in terms of which is better? Seems like just swapping out the valves would be cheaper and easier than having new seats pressed in, so I'm wondering why everyone I know does seats instead of valves.

Ed

[ 12-26-2001: Message edited by: slayte ]

The hardened exhaust valve seats and stainless steel exhaust valves.All GM engines made in the last 60 years and maybe longer had stainless exhaust valves from the factory when new.If you have any doubts about the valve condition, replace them.

[ 12-26-2001: Message edited by: Tony ]

I found some great info on another site!!
Sign up free for this super-forum on Chevy restoration/preservation at... VCCA CHEVY FORUM

I just went thru an extensive ordeal with this issue. I had head work done on a 1952 235, and a 1954 235 Chevy truck motors.

Here is my conclusion based on 3 machine shops and advice from 3 mechanics/machinist with over 100 years total experience.

The stock Chevy exhaust valves, as Tony said, have the lower valveface portion consisting of a stainless type alloy as they will NOT pull a magnet; the upper stem will. These valves do get burned, but that was common with leaded gas use.

The problem with running unleaded gas IS NOT that it is just "unleaded" but it often contains seasonal, emmission, or methanol additives. Worse yet, cheap "discount" gas goes rotten-super-bad over time! These additives really gunk up on an old low rpm, seldom run valves. Thus the problem of burning out valves isn't eliminated with the stock stainless valves.

The real problem is the erratic "detonation" of some of the unleaded gas (ie cheap gas)used in an old engine that "super heats" the valve seats. The newer model truck seats are often factory "flame hardened" to resist this heating and subsequent "cracking" but it still happens a lot in newer trucks and cars. What happens is that the valve seats get real hot from the unleaded erratic detonation (some say because of lower octane), anyway the red hot seats get pounded by the exhaust valves and become either cracked or very malleable. Both bad news.

The old leaded gas both raised the octane AND provided the valves seats with a "lube" or "cushion" of depositions. New unleaded does not.

Cracked seats really show up in newer Marine 454 Chevy engines. This is because somebody uses "discount" gas, runs the engine full throttle most of the day, then pulls a 3 skier load. WHAP! The valve seats are pounded into mush.

Our old stovebolts are mostly low compression engines that can burn relatively crappy unleaded gas of low octane without showing head cracks under magnafluxing. We don't often pull a heavy load in these antique trucks! BUT if our engines have been bored to replace worn pistons; or milled to reshape a minor head warp then the compression ratio goes UP and so does the risk of cracking seats! {My old stock 1952 bored to .060 with the stock head is now a 244 CU/inch with close to 9.0:1 compression! Just cause of the bigger pistons!}

The hardened inserts will expand at the same rate as the cast iron head , which is great, and they will provide a hard "anvil" like surface for a pounding exhaust valve to hit, even with overhot crappy fuel burning. This is VERY important in an old truck running at highway speeds with the stock/high rear axel ratios. Running a mid 1950's or older Chevy 6 cylinder beyond 3400rpm for extended periods really stresses the whole engine and especially the old valve train!

In conclusion, I chose to have the hardened exhaust valve inserts put in at a extra cost of about $75-90. I want these valve jobs to last as long as possible and I just don't know the direction that future gasoline mixtures at the pump will take. I want the old stovebolts to run well into the 21st century and hardened seats were cheap insurance and an inexpensive engine update that may help the old truck pull a load; or better yet just not give any future valve/head problems.

I will also burn "name brand", good quality, higher octane unleaded gas. Just in case!

PS..Lead substitutes work A-ok in stock engines that don't YET need a valve/head job: BUT are a bit "dirty" in deposits on the valves,pistons, and plugs. Who knows how long the EPA will allow them? Use em' till ya need a valve job , then inserts.

Tony,

That is excellent information, thanks.

To get back to my question: why did you choose to use hardened seats, rather than hardened valves? Please note that when I say hardened valves (also sometimes called "no-lead valves"), I am not referring to stock stainless valves.

My post referred to an article written by Jim Richardson in the Classic Auto Restorer Magazine. It says that in order to fix the bad gas/no lead problem which you described so well, you can do one of two things:

1) Put in hardened valve seats (which you did)

OR

2) Put in hardened valves, which is cheaper, and his recommended solution.

Everyone I know, like yourself, chooses number 1, and I'm wondering why this is.

Ed

Hardened valves?Yeah maybe thats what some guys call them.Exhaust valves are generally made from forged 21-4N stainless steel,with or with out chromed stems, depending on the application.They might be heat treated. Your engine machine shop has catalogs showing the types of valves for your particular engine.Take a look at the specs listed. Like Johnny says its the seats that take the beating from high temperatue erosion. Replacing the valves only is bad information if your engine's seats are plain cast iron.The new exhaust seats are a good idea anyway as usually in older engines the seats are worn and recessed into the head.I also know of unaltered engines run at moderate speeds for many miles without valve problems.The exhaust seats in my old trucks were replaced when I rebuilt the engines.

Slayte;

Just replacing the valves alone sounds "thrifty" and inviting, but as Tony and Lil'Johnny said, (paraphrased), the valve train is only as good as it's weakest component.

If you're upgrading, go all the way- hardened valves, hardened seats, and bronze guides. Yeah, it'll get pricey at first, but in the long run, you'll be rewarded.
Take a little comfort in the fact that this just involves the cylinder head on a Chevy; guys like me who insist on playing with old MoPars with flathead engines have to yank the whole engine to get this same job done!



Good luck!