Several people have been PMing me for advice on mechanical dilemmas which have stumped their local mechanics. On several occasions, they were ultimately resolved by a valve adjustment. This explains why. Now, it doesn't matter what kind of machine it is. Ironhead Sportster, CBX or EX500 the theory is the same. This assumes you have a nodding familiarity with a four stroke, internal combustion engine.
Valves 101.
What is the importance of a proper valve adjustment?
A valve is designed to have a certain amount of clearance specified by the vehicle manufacturer. This specification is determined by the type of actuation system, but it won't be zero. Insufficient valve lash causes many problems, among them valve burning and loss of compression. Valves burn because insufficient lash holds them slightly open. They don't have the opportunity to transfer their heat to the cooler mass of the cylinder head. The heated exhaust gases erode the heads of the exhaust valves causing compression loss. The damage is permanent.
Valve lash will never increase. Valve seats pound into the surrounding cylinder head by the normal operation of the valves. This means valve lash closes up, until the lash goes to zero. Effectively, the valves stay open.
Before this happens, the machine becomes hard to start. This also causes problems which are masked as carburetion problems.
These problems are avoided by setting the valves to the loose side of the factory tolerance. The folks who make motorcycles know way more about making them than I do, the intervals they specify are decided by testing.
Valves 101.
What is the importance of a proper valve adjustment?
A valve is designed to have a certain amount of clearance specified by the vehicle manufacturer. This specification is determined by the type of actuation system, but it won't be zero. Insufficient valve lash causes many problems, among them valve burning and loss of compression. Valves burn because insufficient lash holds them slightly open. They don't have the opportunity to transfer their heat to the cooler mass of the cylinder head. The heated exhaust gases erode the heads of the exhaust valves causing compression loss. The damage is permanent.
Valve lash will never increase. Valve seats pound into the surrounding cylinder head by the normal operation of the valves. This means valve lash closes up, until the lash goes to zero. Effectively, the valves stay open.
Before this happens, the machine becomes hard to start. This also causes problems which are masked as carburetion problems.
These problems are avoided by setting the valves to the loose side of the factory tolerance. The folks who make motorcycles know way more about making them than I do, the intervals they specify are decided by testing.