BRONZE ALLOYS

Recent Phone Call….

Customer: “Send me some bronze valve guides!” And I don’t want any of those fancy alloys I just want bronze!”

JRC Parts Counter: “Sir, bronze only exists as an alloy.”

A recent call from a dealer took me down the road of valve guide materials. So I thought why not write an article covering materials currently being marketed. This article will be on red metals (copper alloys named for their reddish appearance).

Copper was one of the earliest metals discovered.  The Greeks and Romans made it into: tools, weapons, adornments, and there are even historical details showing the application of copper to sterilize wounds and purify drinking water. Today it is most commonly found in electrical materials such as wiring because of its ability to effectively conduct electricity. In nature it is often found in natural occurring alloys. To achieve purity it must be smelted using modern or ancient methods. Pure copper will be found on a British bike only in: copper washers, head gaskets and the wiring harness. All other applications will require alloys which have higher wear resistance.

Copper and its alloys are used extensively on engines for: plain bearings, bushings, and valve guides. Copper has too many alloys to list them all here. We will focus on a few of interest to the British bike restorer. Mostly valve guides and bushings.

Bronze is an alloy that consists primarily of copper with the addition of other ingredients. In most cases the ingredient added is typically tin. Arsenic, phosphorus, aluminum, manganese, nickel, and silicon can also be used to produce different properties in the material. All of these ingredients produce an alloy much harder than copper alone. Bronze is typically characterized by its dull-gold color (brass is typically a bright golden yellow). Both may turn a dull copper reddish hue when heated above 400F.

Bronze valve guides were introduced around the time cylinder head material changed from cast iron to aluminum. The job of the guide is: to support the valve, and also conduct heat from the combustion process. This heat is taken out from the valves and into the cylinder head where it can be radiated away by the cooling system (cooling fins in our case). A balance between stiffness and wear on the valve is essential to achieve a useful service life.

This ability to remove heat is often expressed as the thermal expansion coefficient.

Thermal expansion coefficients expressed as the exponent 10 to the negative 6th power(10-6 in/in degrees F).

Cast Iron is a 6,  Aluminum a 13, Manganese Bronze 12, C630 (Ni-Al bronze) 9. We use these differences in heated expansion rates to remove guides and bearings. There are advantages to using materials of similar thermal expansion. A guide with a higher coefficient with be more effective at removing heat. Apart from the expansion qualities of the different metals; are there any advantages of bronze valve guides over cast iron?

Guides made of Ampco 45 or CDA 954 aluminum bronze will outlast iron guides and plain steel valves 2 to 1- when matched with a hard coated or chrome plated valve stem.

Cast iron guides can damage the hard coating on Black Diamond valves. So uncoated stems or chrome plated valve stems [if you can find them] are more desirable with iron guides. There are other advantages: in the event of a bent valve, the bent stem can strain the guide breaking off pieces inside the cylinder. Bits of cast iron guide in the cylinder will cause potential damage to all parts present. A bronze guide is more likely to stay in one piece if it cracks at all. For this reason higher revving race engines will usually have bronze valve guides.

Common Valve Guide Materials comparison:

Hidural 5 (Triumph OEM guide):

copper-nickel-silicon alloy developed in WWII for high performance bearing applications, including main bearings in the Merlin engines in Spitfires. Considered to be close to factory for our British bikes. I have it on good authority that Hidural 5 was used for valve guides at Triumph.

95% copper, 2% nickel, .8% silicon, 0.5% zinc, 0.10% iron

C630 (Ampco 45) Aluminum, Nickel, Bronze:

Can be really difficult to ream without the proper sizing tools and set up.

85% copper, 11% aluminum, 6% nickel, 5% iron, 1.5% manganese

Manganese Bronze C863:

Lacking nickel and iron, plus the addition of lead, make this alloy easier to ream and hone than C630

60% copper, 34% zinc, 2.5% manganese, 2.2 % lead, 1% silicon

Colsibro® is a precipitation hardening copper nickel silicon (new to British bike market – and rather expensive):

Colsibro material is a copper nickel silicon alloy, and is second to none as valve guide material. Has high wear resistance and heat conductivity, and the lubricity prolongs valve stem life. Some shops are now making repair valve seats from this material.

97.4% Copper, Nickel 2.0%, Silicone 0.6%

This ones a bit unusual as the name is misleading.

CW713R High Tensile Brass:

(called brass because by definition it contains less than 60% copper and the zinc composition exceeds 30% )

CW713R (CuZn37Mn3Al2PbSi) is a high tensile brass which is alloyed with aluminum, manganese and silicon etc. which makes this alloy almost as hard as aluminum bronze, but considerably easier to process. CW713R also has good corrosion, wear resistance and machinability. Andover Norton markets “go faster” guides that are comprised of this material.

59% Copper, 35% Zinc, 2% Manganese, 1% Aluminum, 1% Iron, 1% Nickel, 1% Silicone, and < 1% Lead

Non-Bronze copper-zinc alloys:

Brass is mainly an alloy that consists of copper and zinc. Some trace elements me be added as well. These varying mixtures produce a wide range of properties and variation in color. Increased amounts of zinc provide the material with improved strength and ductility. Brass can range in color from red to yellow depending on the amount of zinc added to the alloy. If the zinc content of the brass ranges from 32% to 39%, it will have increased hot-working abilities but the cold-working will be limited.

Brass (260 formable) is commonly used for decorative purposes primarily because of its resemblance to gold. On British Bikes it will be found in limited use. Mostly in the electrical system as contacts or terminals. Styling items such as tank trims and instrument bezels typically are chrome plated brass. Brass (such as 360 ultra machinable) makes very poor valve guides. Years ago a vendor supplied a batch of, easy to machine, “bronze” valve guides. These didn’t last long at all in our test engine. So if you find cheap valve guides for sale be suspect of what material they might be. The added metals are where the expense of bronze is at.  Otherwise you might be doing that top end job again real soon.