Valve material

I am helping to complete a Centaur gas engine that a friend purchased partly built. I have just discovered that the valves, while well made, are non-magnetic. Does this mean that they are of stainless steel? Would this necessarily mean that they need to be replaced?

Maurice

I would think, if they are stainless they are probably OK . Stainless usually has a higher temperature resistance than mild or plain carbon steels. In small model engines I don't think it matters too much what they are made from because smaller engines dissipate heat better than large ones. Many model four strokes run with valves seating directly onto the alloy cylinder head and they have no problems.

Thanks Bob, that is reassuring. I've had to remake enough parts already, due to poor workman ship. I don't need any more to do.

Thanks again

Maurice

Its when your engine is really doing some work, and the exhaust system is glowing that nice cherry red that all the tool hardening instructions go on about, that is when you need to worry about what your valves are made of.

By which time the shed will also be warming up nicely ...

Cheers, Tim

I have doen lots of engines with stainless valves from slow running hit & miss types to faster aero engines so you should have no problem.

Stainless seems to be the material of choice for model IC engines.

On large IC engines, motorcycle to aero, it was the material of choice after WW1. Since then a large number of valve materials have been developed. Most have their ancestry in stainless. The quick way of identifying an exhaust valve (ordinary 1950s motorcycle engine) was to see if it was non-magnetic.

JA

I run stainless valves in my full-sized Harleys so I imagine it will be OK for a model too.

I don't know where this myth that stainless steels are non-magnetic comes from.

There are three basic types of stainless steels. All stainless steels are normal steel with some chromium and/or nickel added to increase there corrosion. Of the three basic types there are:

Ferritic stainless which is magnetic, non-hardenable and easy to machine

Martensitic stainless which is magnetic, heat treatable, enhanced strength and relatively easy to machine

Austenitic stainless which is non-magnetic, very hard and strong, far more difficult to machine but has high corrosion resistance.

Some type numbers:

Ferritic 430 & 430F

Martensitic 410, 416, EN56, EN61, EN62 & EN57

Austenitic 303, 304, 316, EN58, EN58A, EN58B, 440 & 440F

As well as chromium and nickel additions some types have niobium and titanium to modify the characteristics.

Generally to be classed as a stainless steel the alloy must include at least 10% chromium. Also note that stainless steel is exactly what its name suggests, it is resistant to staining by chemicals, it is not necessarily rustless or resistant to corrosion. Some grades of classic stainless steel do in fact corrode when sea water or other mild chemicals are present. A common use of 316 steel is battery clamping bolts which has the highest corrosion resistance, but 316 has a lower tensile strength than other types. 316 compared to a normal high tensile bolt is only about 40% of the tensile strength, so care needs to be used when critical applications are encountered!

Surgical scalpels and other cutting tools such as knives are traditionally made from 410 as it is heat treatable to harden the edges.