Guidance for the valve stems: valve guides

Valve guides look inconspicuous, but they have an important task. If the valve is not guided correctly, it cannot open properly and it does not seal properly on its seat. Both are important if the engine is to produce its optimum performance. In addition, valve guides and valve seats must dissipate the heat from the valve itself and transfer it to the material of the cylinder or cylinder head.

How often do valve guides need to be replaced?

Provided they are well lubricated, valve guides can last the life of an ohv engine. The oil supply in the cylinder head must be correct. The valve stem seal should only prevent too much oil from reaching the valve stem. Too much oil in the valve guide not only works its way into the combustion chamber and causes the exhaust gases to take on colors ranging from blue to gray to white, no, it also tends to bake into the exhaust valve guide and reduces the service life of the guide and valve stem as carbon deposits.

Valve guides have a much harder life on side-valve engines and IOE models, which is why at least the exhaust valve guide has to be replaced after around 25,000 km. Especially if the biker has always been riding fast. On these models, the valves and guides are lubricated solely by the oil mist that gets past the tappets and under the valve spring cover. The inlet valve guide of IOE models is prone to wear. Its life is largely determined by the oil can, which the rider should have with him on long tours.

How do you install valve guides?

It is said that there are brutal people who simply knock the guide out of its head with a hammer and then force the new guide into place with just as much force.

The correct way is different: The valve guide has a press fit in the cylinder or cylinder head. That's why cylinders or heads are first heated before the old guide is pushed out. This way you prevent damage to the material. In the same way, cylinders and heads are heated before insertion and the guides are cooled before they are pushed in exactly concentric with the valve seat using a special tool. This method guarantees that the guides do not become loose even under thermally difficult conditions.

What needs to be considered with valve seat inserts?

Despite being inconspicuous during operation, valve seats are wearing parts, as the valve head hammers on the valve seat 1,125 times a minute at 2,500 rpm. When a valve is removed, the valve seat is also inspected. The tightness of the valve depends on the geometry of the valve seat. And if this is worn, valves no longer seal correctly. The valve seats must be checked urgently at the latest when the valve clearance changes itself every few hundred kilometers. This is because they are usually already loose when the engine is hot.

Work on valve guides and valve seats is always a case for a specialist, especially if you don't have the tools. Contact your trusted engine rebuilder.