valve seats

[NC Cams]

Some fundamentals:

Force is pressure divided by area - you know PSI type force thing.

In IC engines, there are two primary forces that affect seat integrity - seating force from the cam and/or the pressure acting on the valve head by the combustion gasses.

Seating forces = if you drop a glass, it may or may not break. It essentially depends on how hard it hits the floor and how much force is applied in the process. The same sort of deal affects the valves.

The seating forces are a direct result of the cam profile dynamics (not adjustable by you) in concert with the lash (which you can select/adjust) being used. More lash generally fosters harder/violent pounding and vice versa.

The magnitude of the force tolerable ultimately depends on material selection.

Combustion pressures = if you take the same cylinder pressure (say 600psi) and apply it to a valve that is 0.125" diameter, the amount of seat force is HUGELY different than what the same pressure would generate on a 2.02" diameter valve. I'll let someone else do the math to get the full effect of the magnitude of the force differential between that applied to a 2.02" valve compared to that of a 0.125" diameter gem - can't find the calculator.

When the net force applied to the seat by the valve exceeds the yield strength of the materials being used, the seats will start to deform - whether the force comes from gas pressure or from cam induced seat hammering, force is force.

Depending on the stresses generated by valve to seat contact, you could use aluminum - if the forces get too high, you can't find a steel strong or hard enough to endure the carnage that ensues.

Where the limit exactly lies necessitates information that has not been provided in the discussion thread.

Don't forget that as metals get hotter, their strength diminishes as does their yield points.

NOTE: valve seat geometry gets into the picture as well (wide vs narrow seats, 30 deg vs 45 deg). But that takes the thread outside of the scope of the original inquiry and greatly ads to the complexity of the discussion.

[T.L.A.R. eng]

I think you answered the question NC CAMS about scaling forces down to the little engines. Comparing a .373 valve to a 2.02 sbc valve isn't comparing apples to apples. I agree with you.
I have ajusted the cam profiles some because I grind my own cam profiles.
Long opening and closing ramps are easy on the seats, but not good for making power. We want to smash the valve open, then smash it back shut for maximum flow. Excessive valve lash works for this as long as there is enough duration ground into the cam. E.G. the old Duntov 30-30 cam for the sbc. .030 clearance on both intakes and exhausts, mechanical lifters of couse. Sounded terrible but really woke up the small block.
I agree, this could really open a can of worms. There is allways a trade off when dealing with mechanical engine part design.
I have viewed the Forrest Edwards radial plans, and it uses aluminum for the seats, so I guess I will use the aluminum seats on the Kinner K-5 and see what happens.

[Ivy McNeil]

Hi Guys

I am building the Edwards 5 Radial and I ponderd the issue of valve seats, I did install brass valve guides and if I find a problem with the alum seats I will install harder seats.

Ivy McNeil

[Bill Johns]

I have machined all kinds of exotic materials. Stellite is not all that bad, we used ingersol carbide tools and data flute end mills.
Diamond tools for Al??????? How about carbide?
For a valve seat in a model engine, even a low grade steel or something like
303 or 304 stainless would be fine. I would not use Al or bronze.

[Pres]

Since most of the exhaust valve cooling is provided by the valve seat it seems that a material with the highest thermal conductivity would be preferable.
Of course, the metal must be sufficiently strong to give reasonable service life.
Also selecting a material that more closely matches the expansion rate of aluminum is preferable.

Al or Al/bronze would be my 1st choice.

Cast iron would be a last resort.

Pres

[bowber]

A now defunct italian motorcycle manufacturer used to make their racing engines using no valve seats in the Ali head, they mainly made 250 singles.
They ran the motor for a while to work harden the seat and then the head would last for the whole IOM TT, even then they claimed they only changed them to be sure.

Advantages were the direct heat transfer and ease of manufacture.

I've also used plain 316 stainless for valve seats in racing engines, admitadly speedway engines but they are still going years later and they get hammered from start to finish.

As has been said just do it and check the clearances, they will settle initially as the valves bed in but then I think they will last ok.

Steve

[Bear]

Woo Hoo !
Bear here, what interesting vague...
answers ? Unless the correct, solidly
mounted, rotating rolling devices are
used , to obtain the correct sealing from
an angled mechechenism to another cannot be obtained,
let alone to sum sutch silly questions as materials
commoniers (sutch as myself ) have access to
or are capable of understanding or using.
Cork on a string!!!

[balsaman]

Huh?

[Bear]

Bear,
being facious,as some here have never been to an antique
tractor ,"old" machine,"old" machinery showing(in field type).
There were many types and styles still in operation taken
care of by people who have rebuilt many of these engines
and maybe dont know what they are doing(by some paper,
or wanabe paper eniginers) will not work.

I apperiate the knoweledge these old uneducated
geniuses

Bear

[bluejets]

Bronze has been quite sucessful for the engines I have built. One aspect being ease of machining. One important thing to remember is, when the guide and the seat are made as one unit, everything is kept true.
I have to agree with "Pres" above though as recently I have had the opportunity to get off-cuts of Al/Bronze from a company here that builds ultralight engines and found it to be just as appropriate.

[stevehuckss396]

Originally Posted by Hiredgun i noticed most people seem to use brass or something for valve seats, the aluminum on a head made of 6061 t6 will not work? i plan on building a v8 to put in my 6ft long remote controlled boat. second will pistons made of 6061 hold up?

Go with the bronze. I am building my first engine and bronze was very easy to work with. I was told when pressing in the guides, use a drop of red locktite for extra insurance.

I made my pistons from 6061 also. Both materials were purchased from a scrap/recycle yard down the road.