Originally Posted by russxr67
When these engines were designed, leaded petrol was the choice of fuel and it is the lead portion which acts as a "lubricant" to slow down the process of erosion on the seat as it was just cut into the soft cast iron.Unleaded fuels such as gas and modern bowser petrols do not have this lead and if used without hardened seats will quickly wear the seats away ,causing valve seat recession.I can,t say how long it will last if you opt not to go the hardened seats route but i have witnessed first hand what can happen to your seats after prolonged use.Any clev that i build these days if run on the street gets the hard seats.
Just to expand on this a bit...
When the valves close at significant RPM (above about 2500), they tend to bounce up and down on their seats a few times before finally settling and staying closed. This can be demonstrated by taking a hammer and whacking a chunk of steel/iron with it...like an old railroad track, anvil or broken engine block or cylinder head. What happens is that the face of the hammer bounces a couple of times after hitting it even though the spring pressure in your arm is trying to push it solidly closed. At higher RPMs, the bouncing lasts a bit longer and at lower RPMs it is shorter. Just like spanking the chunk of iron with the hammer, a noise rings out inside the chamber when the valves "bang" themselves closed. This is the reason that harmonic dampeners are used in valve spring assemblies. They absorb the sound waves coursing through the solid stem of the valve and help control the valve better by dampening the effects of those harmonics.
And, just like the engine block being whacked by the hammer, there is a pit left in it everytime you give it another blow. This is what happens to valve seats over time. Softer seats get "peened" into the head, which results in what is commonly called seat recession. The cure for which has been to cut out the cast iron and press in hardened steel seats so that the valves and the seats tend to be of about equal hardness. This is like taking two steel hammers and banging them together. It produces a hell of a shockwave, but the similarity of the two materials means that neither is the victory over the other.
Two-piece valves are a bad choice for nearly any performance-minded application. Use high quality stainless steel valves for better results.
Use a top oiler for lubrication. To say that leaded fuel is a good "lubricant" is a bit misleading. What happen(s/ed) was that lead deposits formed around the seat of the valve and on the valve edges themselves such that when the two banged together they met with a nice squishy layer of lead between them to cushion the blow. Anyone who regularly uses leaded racing fuel knows what I'm talking about. This stuff gets everywhere! The pistons get coated with it, the intake passages get coated with it, the stuff is like honey--stuck everywhere and gumming up the place! Anyone ever heard of GUMOUT? It was a spray cleaner that was commonly used to remove lead deposits from carburetors and other places.
See the first page of Gumout Web Site
...it goes: Several years ago, Gumout« became the leading carburetor cleaner.
The reason was because several years ago (going on quite a number now!) carburetors stopped showing up on new vehicles AND because leaded fuel stopped showing up at the pumps. You can imagine just how PYST they were when leaded fuels were abolished!
While the world is probably better for it, valves and seats have taken most of the abuse. Carbs, on the other hand, don't gum up much at all anymore!
During combustion, most of the lead was vaporized but some deposits were left behind to eventually build up over time requiring attention after many several thousand Ks...typically about 80-100K-km. Engine builders would essentially have to wire-wheel the heads, with the valves still in them, into submission in order to see what they've got to work with. It used to be rather common to "hot tank" everything in an acidic bath and go back in with new "soft parts" in order to save time and increase production rates of head refurbishments. Of course, environmentalists have just about completely outlawed those materials due to their waste requirements, but it is fun to remember the days when every mechanic's shop had a large drum with parts hanging from wires going into it. Boy you sure could clean things up easily! (Except the drum!)
Like points ignitions, times have changed and using "soft" seats are a thing of the past. A few of us struggle to hold on to the past in spite of the changing times. A quick look around will tell you that the pushrod V8 is a thing of the past. Every rice burner on the planet is running on piss and sake and making better mileage, running in the half-million Kms between overhauls and we're talking about going another 100,000 or so at best.
Of course, there is something incredibly sweet about pulling up next to one of those sewing machines at a traffic light with the old V8 iron rumbling out a bad-ass tune. I (used to) love driving my Mustang through the pits and setting off all of the car alarms on the stupid rice wagons with their fart cans and 4 different colors of primer for their "ground effects" shite bolted on to their POS cars.
A good friend of mine and I spent one night at the track on "ricer night" practically howling with laughter after a session of producing our vocal renditions of ricer fart pipes to the tune of "farrrrrrrttttt....ppppiiiiipppppeeeee" over and over again admist about 10-12 of them running somewhere in the high teens...which culminated in my asking my mate, "do you know how to make a rice burner run a 12 second quarter? ...pull it behind a 10 second Ford!"
You know you're old when you're out at the track with more electronics going on than a space shuttle launch and a high school kid in a mostly stock classic Mustang more than 20-years older than him...drives by running like crap...and you flag him down, have him pull into your pit area and tune his car up and show him how to set his points, lash (stock solids!) and timing. But it is worth the shit-eating grin on his face when he comes back waving his timeslip around like it was a winning jackpot lotto ticket after running a 14.8 when having done nothing but high 16s and low 17s in it. Yep...another convert to the glories of the pushrod V8.