I've got a Honda Xl600LM, '87 model, and when it is started from cold there is a tapping sound from the top of the engine. As the engine warms up it become more intermitent, until it stops after about 10 minutes. It has a definate "rhythm" to it, and as the engine warms up the "tapping" fades in and out, becoming less until stopping.
The valve clearances are as the Haynes manual recomends, it's done 35,000km, has a handle bar and kick start decompressor on it.
A friend suggests the noise might be piston slap, but as it's coming from the top of the engine, and not from around the barrel area i'm not sure it is?
any help would be much appreciated