What is the advantage of bronze valve guides?
They can be machined to tighter tolerances, and bronze is a softer metal than steel. This means it will seal better but wear quicker. Also, bronze probably reduces the friction of the valve stem to guide interface.
What valve guides last the longest?
Cast iron guides work fine and are easy to install, last a long time, and may be clearanced with a reamer. Bronze guides require more clearance, must be clearanced with a hard stone wet hone (Sunnen type), and need to be installed by someone with MG specific experience and the proper equipment.
What is the main purpose of the valve guides?
A valve guide is a cylindrical piece of metal, pressed or integrally cast into the cylinder head, with the valve reciprocating inside it. Guides also serve to conduct heat from the combustion process out from the exhaust valve and into the cylinder head where it may be taken up by the cooling system.
What are valve guides made of?
Sintered or powdered metal (P/M) valve guides are typically made from low alloy steel grades containing mainly iron-copper-carbon and exhibit ferritic/pearlitic microstructures. Compositions containing higher carbon levels ( ie more than 1.6%) exhibit carbides and free graphite. Copper levels may vary from 2 to 12%.
What are the three types of valve guide seals?
Either way, the engine is going to have problems.
- There are three types of valve guide seals: umbrella, positive, and O-ring [ see Figure 4 ].
- The umbrella seal, used on many older engines, fits snugly over the valve stem.
- The O-ring seal was used on many millions of older General Motors engines.
Which type of valve guide is most used in a cast iron head?
On the automotive side, PM is widely used as well as cast iron. Bronze valve guides are still widely used in European applications.
What is the best valve guide material?
Manganese bronze works great with higher valvetrain speeds and offers great corrosion resistance. The material make up of manganese-bronze guides generally consists of 55% copper, 40% zinc and 3.5% manganese. As far as any other materials used in performance, manganese-bronze is still the best choice for valve guides.
What are the 2 types of valve guides?
Valve guides can be generally classified into two groups: cast iron and manganese bronze, which covers a wide range of applications.
What happens when valve guides are worn?
Worn guides can also contribute to valve breakage. The guides support and center the valves as they open and close. A worn guide will allow the valve to, wobble slightly as it opens. This will cause it to drift off-center with respect to the seat.
What are the two types of valve guides?
How are valve guides lubricated?
Different than other seals in the engine, valve stem seals play an important role in lubrication. Valve stem seals allow a controlled amount of oil to lubricate the valve stem as it moves in the valve guide. The amount of oil that passes by the valve stem seal must be precisely controlled.
What type of valve guides are there?
Valve guides can be generally classified into two groups: cast iron and manganese bronze, which covers a wide range of applications. Cast iron guides are used mostly by OEMs due to its wear characteristics that result in longevity for high mileage applications.
Can a bronze valve guide be used in a cast iron head?
Many after market suppliers extol the virtues of the bronze or silicone bronze valve guides that they sell and, although these may wear marginally more slowly than cast iron valve guides, it is my belief that bronze of any type is not an ideal material to use for exhaust valve guides in cast iron heads.
Are there any drawbacks to making valves in bronze?
One drawback of bronze is that valves can only be produced by casting, or by machining cast ingots. The rough exterior of bronze–which is known for porosity and shrinkage cavities–is a direct result of casting (though bronze alloys containing nickel, lead, and bismuth will hold a polish).
What kind of metal is used for valve guides?
Cast iron is used because it is a very dissimilar metal from any used in valve manufacture – important to eliminate galling that causes seizure of the valves in the guides – is softer, yet resilient enough to wear well. Bronze, on the other hand, is a very general description as there are a variety of ‘bronzes’ used by various folk.
What kind of guide do you use for a valve stem?
Cast iron guides are used mostly by OEMs due to its wear characteristics that result in longevity for high mileage applications. Cast iron is used with chrome valve stem applications as well. Cast iron cannot be used with stainless steel because of its tendency to gall.