by John R » Wed Nov 18, 2020 8:38 pm
Thanks. The ’72 spring will help to turn the light off but pressure will need to build higher to open the check-valve – till then, no oil-flow to the engine.
Understood that Ks/XLs have very little resistance to oil-flow, but you still need a modicum of pressure to ensure flow, and if your oil light is on at 50mph on a hot day, you don’t know whether you have that modicum or nothing. The oil-switch turns out the light at just 3lbs/sq.in. Low oil in tank is more likely than total pump failure, but you don’t have the peace of mind of 3lbs+, just an act of faith!
The running pressure in Big-Twins is higher as the flow through the pinion shaft to the big end is side entry via the bush into a 1/16” hole in the side of the shaft, so that there’s just a small pulse of oil once every revolution, and the big-end assembly is happy with small rations.
Ks and XLs have end-feed which is continuous through a 1/8” hole (though reduces within flywheel assembly). If the pinion-shaft bush is worn, oil flows direct into the gear-case through the clearance – even less resistance for pressure to build against.
As an experiment I fitted a restrictor into the end of the pinion – a brass plug with a 1/16” hole – but still it’s continuous flow, now the oil light is out above 40mph on hot days. Thought about a smaller hole but then too easy to get blocked.
It’s a hobby so overcoming these H-D fads is part of the pleasure. Checking through every last detail of the pump to figure out how it can be brought to best condition.
BTW – the check valve opens at about 1¾lbs/sq.in. to allow oil-flow to the engine, so if pump is not creating at least that behind the check-valve, the engine gets no oil at all.
The oil-switch responds to pressure before the check-valve. If the oil-light flickers it shows that pressure is in a cycle. The pump builds pressure to 3lbs+ which will open the check-valve and turn the light off, but with the check-valve opening to an almost no resistance route, the pressure collapses and the oil-light comes on again. This cycle repeats almost instantly and continuously till pressure rises above 3lbs in the entire system, and the light goes out.
So a flickering light means operating at 1¾ to 3lbs, which is enough, but a solid red light could be bad news. An oil-switch that works at 1½lbs would be ideal. Is there one out there?