valve seats

[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?

[nick.gilling]

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.

[NC Cams]

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.

[balsaman]

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

[Geof]

Originally Posted by Hiredgun 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.

[thkoutsidthebox]

• 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 parts

http://www.reade.com/products/Alloys/stellite.html

[Geof]

Originally Posted by thkoutsidthebox 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 parts http://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.

[itsme]

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

[NC Cams]

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.

[vulcom1]

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

[Pres]

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

[T.L.A.R. eng]

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?