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?

I've never heard of aluminium valve seats, they always have an insert of some type, don't think brass is the norm either.

Aluminium should be ok for pistons though, that's what they are in most engines.

Common "real" piston, piston alloys: 4043 or 2018, either are most commonly used in forgings.

Hypereutic alloys are now being used in some rare forgings and, more commonly, castings, especially 2 cycles.

Hypereutectic alloys are harder to machine (diamond tooling required) but have better hot strength due to additional silicon.

Typical valve seats: ductile iron, silicon bronze or straight cast iron.

You might get away with 2024 aluminum for pistons and/or or head but that depends on how much heat you generate.

Some guys machine the seats into aluminium heads and it works for running "display" type engines but I doubt it's a good bet for a "perfomance" engine like one you would like to build to run in a RC boat.

E

i noticed most people seem to use brass or something for valve seats,....

It is the 'something' and almost certainly Stellite if you have seen valve seats that had a brass type appearance. Very hard high melting point alloy that I think can be called a bronze. Interesting stuff, I seem to remember you can get Stellite rods that look, feel and work just like bronze welding rods but once they have been melted and re-solidified the properties change so it is very hard and has a higher melting temperature than the first time.

Stellite Typical Applications:
Aerospace= vane plugs, fuel metering pins, spacer bushings.
Bearings= ball blanks and race blanks
Valve Seat Inserts= duesel engine exhaust and fluid valve seats
Saw cutter inserts
Miscellaneous wear partshttp://www.reade.com/products/Alloys/stellite.html

Stellite Typical Applications:
Aerospace= vane plugs, fuel metering pins, spacer bushings.
Bearings= ball blanks and race blanks
Valve Seat Inserts= duesel engine exhaust and fluid valve seats
Saw cutter inserts
Miscellaneous wear partshttp://www.reade.com/products/Alloys/stellite.html

And rebuilding motorcycle rear sprockets when the part is no longer available. Real b***h grinding the tooth profile adequately with a handheld die grinder though.:)

Hi there,

I know it is not uncommon for DIY model engine builders to make the valve seat and guide all in one piece out of bronze. I have used this method on a slow running, low power engine with good results. The guide and seat is turned and then pressed into the head. I'm not sure what the limitations are on this method with regards to higher performing engines.

Regards
Warren

We grind stellite hard facing all the time - it is blatant overhill and not something to even seriously consider for a DIY built R/C engine.

Besides, machining of the stuff is all but impossible, you will have to grind it, especially if you weld it into place as they do on steel valves that are hard faced. Stellite seats are all based on as-cast rings that are all machined soft and then heat treated hard and then finish ground to size.

If you can get a hold of an SAE handbook, you can find pretty much EVERYTHING you want/need to know about engine valves and/or valve materials in SAE spec J775.

In the latest SAE handbook, very near the J775 spec, they also list pretty much every guide and/or seat material known to man in two separate specs.

When it comes to valve materials, simply saying "bronze" (hundreds of alloys and most won't work) or "stellite" (same thing) nor for that matter "stainless" as in stainless valves (which one? there are many that suck for valves and many that are fine) is hardly adequate nor appropriate.

You need to indicate WHICH alloy or else you'll be in eminent danger of getting something that works for a faucet (bronze) but not worth a damn for a seat or guide.

Sadly, I lost access to the latest SAE manual or I'd give you the SAE specs for guides and/or seats too. The J775 spec is in the manual I have however it has been updated (mine is dated 1992).

NASCAR engines use primarily berylium bronze seats in concert with titanium valves. Steel valves (regular and stainles) are also used with berylium bronze seates. The OEM's use powdered metal seats (many, many alloys) in concert with conventional and stainless valve alloys in their aluminum heads. The prior mentioned SAE specs will identify suitable candidates.

Guides are powdered metal, ductile iron, cast iron and/or alumiun-silicon-bronze. Again, see the SAE spec for specifics.

It is important to note that valve metallurgy, seat material and guide materials are often iteratively developed in engines. That is, they try something economical (simple iron usually) and then start adding the trick, more expensive stuff if/when the simple stuff fails to live or provide the performance required. Amazingly, simple pearlitic cast iron still functions quite well for seat and guide material in many applications.

In light of an R/C engine having relatively SMALL valve head areas, the mechanical and thermal stresses from combustion should be fairly moderate as compared to say a comparable power to displacement ratio'd full size race/performance engine. You could ultimately get away with some pretty sedate materials.

Spend a few bucks and get the SAE specs.

For your application and what I would do is get a piece of cast pipe and machine it to the size you need. From there I would make a seat in the head that is very tight. Heat your alum. head and freeze your seat and press in place. You need a press fit when the seat is cold. I would then stake the seat in and machine the seat for your valve. After lap the valves individualy as per normal. I don't think you have to be to technical for your application but it is nice to know the alternatives.
John

Since its such a small engine, just cut the seats into the head.

The valves are small and your hours of running time is relatively short. IMHO, it is worth a try.

Just keep an eye on valve clearance to start with.

Worse comes to worse, you can always put in seat material later on if seat wear becomes excessive.

Seems like a neat project.
Good luck,
Pres

My experience with the valve seats cut directly into the aluminum head have been goodso far. Excessive valve spring pressure and too much guide clearance will have more of an effect on seat wear than heat will. Does the amount of combustion fire has less effect because of scaling size? Load allso has a direct effect. This is just my own thoughts and observations during testing, A.K.A. 'abusing' my single cylinder 4-cycle home design. Sustained 7000 rpm has shown little seat wear if any. I only use enough spring seat pressure to prevent float. The head is made of 7075 al. The valves are drill rod.
My small coles hit-n-miss allso uses direct seats in the aluminum head. This engine has well over 100 hours on it. I recognize that the valves are off their seats most of the time with this engine, but the intake valve is 'atmospheric' and you can hear it chatter on the seat during the intake cycle. I don't really see any appreciable wear on this engine either. compression is excellent on both engines.
My own experiences are rather limited. I am in the process of building the Kinner K-5 and plan to use aluminum seats, should I use iron seats?
I would like to hear others experience using aluminum heads/seats?

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.

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.

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

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.

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

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

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!!!

Huh?

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

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.

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.