So assuming we have a free moving spring & sleeve with oil flowing towards the crank at full pressure. The oil “sees” the oil feed injector cone with its small central drilling. This drilling is there to restrict flow to the crank & in doing so force oil to flow up the timing cover delivery tubing to the timing gear spindles, cam spindle & rocker gear.
It is worth mentioning at this point that the oil injector cone has a different sized central drilling for the two types of crank in use on these engines. I have seen a cone with a 3mm drilling in use on roller bearing cranks & a 4mm holed cone for the bushed big-ends used on some 175 engines. The bushed cranks are not favoured for hard use (given the low output pumps we are stuck with) & NOS bushed rods & pins are very hard to find. For these reasons bushed cranks are often replaced by roller units – it is essential to use the smaller holed cone when this happens or the rest of the engine will be starved of oil. Conversely, a bushed crank must always have the larger holed feed cone. Back to the plot….
The oil now has two possible routes; to the crank or up the timing cover….well no …it has a third choice. To squirt out between the top of the steel sleeve & the back of the oil injector cone! Unlikely? Maybe, but the Moto Parilla race shop went to the trouble of sealing off this possible route by a simple modification to the standard oil delivery components.
I am indebted to Richard Morley – our GP Rider correspondent – for remembering that this simple mod was done to his race engines by the Parilla race mechanics back in 1964. Small mods like this are employed by race teams the world over – often as a result of bitter experience – so we would be very foolish to ignore their hard-won expertise.
As can be seen from the picture on this page an O-ring & small washer are all that is required. The O-ring should around the parallel section of the injector cone after it has been passed though the steel sleeve. The OD should be such that it clears the ID of the steel sleeve. Before the spring is fitted a steel washer is fitted over the parallel section – a loose fit on both OD & ID.
Usual disclaimers – no guarantees of 10mph more top speed, 1000 more revs or anything at all for that matter. Maybe a bit more oil making its way up to the hard-pressed cam & rocker gear?