Description

Positive Crankcase Ventilation Valves

These PCV valves are only 2inches long and ¾ inch diameter and will fit unobtrusively on your machine.
They have been used successfully on two of our road bikes, single and a twin, and two racing Vincents (500 single and 1275 twin) as well as on our BMW K100 race bike for a number of years, but they are suitable for any machine.

The valve has an input port to take a nominal bore ½ inch tube and an outlet of 3/8 inch. On a Vincent this is normally fitted above the front valve cap with a series D breather cap (ET24/6) and then led along the top of the engine (on some models it is often possible to situate the Valve under the head lug FT3).
An alternative used on one of the racing comets is to retain the timed breather and insert valve on an initial upwards run of the breather tube.

Whatever position is decided, after leaving the PCV valve, the smaller pipe can be run along the machine as required ending either to a suitable container (500cc for UK racing) or follow the normal standard run where an absolute minimum of oil seepage should be encountered at the end.

The one-way action of the valve will ensure that after the initial start a slightly negative pressure will be obtained within the crankcase while the air colum within the breather tube becomes relatively static.

When used on a 1275 racer both front and rear valve caps had these fitted and the mandatory ‘catch bottle’ where they terminated had just a couple of teaspoons of oil inside at the end of the season.

Please note a PCV valve is not a cure for badly worn engine, pistons bores and other engine components can allow excessive oil to be ejected from breathers of any type.

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