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You’ve seen them in the top bearing plates once the valve caps are removed: tiny holes. They are known as “oil ports” or “oil holes”, and they allow you to lubricate the top of the rotor directly.
Oiling the inside rotor facings is easy, since removing a slide gives direct access to the rotor facing. But the bearings need to be lubricated just as much as the inside facings do. You probably simply remove the valve cap and put a drop of oil onto the top of the top bearing stem.
But then you need to either pull the slides to create a vacuum and draw it in, or just work the valves and let capillary action draw the oil in.
The oil port makes it much easier to get oil in that important top bearing. But is there any other benefit? Possibly.
Kendall Betts, Proprietor of Lawson Horns, relates the salutary effects that Walter Lawson noticed years ago. Betts says, “He experimented with various weights and inside shapes of the valve caps. The result [of the oil ports] was a slight change to them as to the inside shape increasing the volume slightly.
He felt, and as I recall he proved on spectrum analysis, that there was a slight increase in resonance as a result.” In other words, the oil port connected the two spaces – the space inside the valve casing and the space under the valve cap – creating a larger volume of space which improved resonance. The use of the oil ports is now part of the “Lawson acoustic”.
So, will it help your horn to have oil ports drilled?
It might, but probably only slightly. The main advantage to oil ports will always be ease of lubrication.