K Models oil pump mystery

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K Models oil pump mystery

Postby John R » Sun Nov 15, 2020 7:59 pm

All parts books from ’52 to ’59 show “26424-52 oil pump oil line plug, 52-54 All K Models”, but my ’53 KK with correct pump doesn’t have anything I can identify as this.

There doesn’t seem to be anywhere where this could go whether threaded or interference fit.

My best guess is that it’s a parts book screw-up and that 26424-52 was a very early part that preceded “26423-52A oil pump plug”. If the original design had been for the by-pass oil through the relief valve to go back direct to the oil tank (rather than via the gear-case) that’s where the oil-line fitting would have been.

So any info or better guesses would be really appreciated. Thanks.
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Re: K Models oil pump mystery

Postby Lisa » Sun Nov 15, 2020 9:00 pm

Rebuilt and modified a few and never seen one with a plug = either had a ball with a threaded shaft to bottom out the ball and acorn nut on the end or a spring and valve in it. Mistake ? Must be in my opinion = again ? Tom pump re builder The wet sumpers that i modify to never wet sump again. K's and ironheads done well over 75 so far no complaints done right.
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Re: K Models oil pump mystery

Postby Coolbreeze » Mon Nov 16, 2020 12:10 am

I would trust Tom's answer. He has worked on more K model oil pumps than I have seen!
'56 KHK
'60 XLCH
'48 Chief
'42 Indian 841
'64 BMW R69S
'84 Moto Guzzi V65Sp
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Re: K Models oil pump mystery

Postby John R » Mon Nov 16, 2020 3:08 pm

Thanks Tom, if you haven’t seen the mystery plug, then that’s good enough for me. You might like to give your opinion on something else.

The end-float of the pump gears provides the escape route for oil to seep up into the engine (via clearance on the shaft) when parked-up (never understood why H-D in ’58 didn’t put the oil-seal in the top plate as well as the body).

The end-float also provides a small escape route from the high-pressure side of the feed gears back to the no-pressure feed side. At slow engine-speed oil-pressure is real low, do you reckon much pressure is lost that way? Or it more about lots of other small factors like wear in the body where the gears have taken abrasive specks through?

Harley gaskets were just 3thou but some after-market are double that, making the escape route even bigger and must have greater pressure loss.

The gears sit just under-flush with the body – wondered whether worth skimming the body to make them dead flush, so end-float is just the gasket thickness. What do you think?

But how good were these pumps when new? Strikes me that the feed gears are thin. Is that a result of the pump unit almost touching the frame?!
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Re: K Models oil pump mystery

Postby Lisa » Mon Nov 16, 2020 4:37 pm

No pressure is involved in a K model or an ironhead they are a flow system as long as the engine has flow you are good to go. When they are cold you will get pressure and as they warm up pressure goes very low unless your RPM is very high then you might get a lil bit and just enough to keep the oil light off at idle. Because they have no back pressure your supply of oil will be adequate as long as your pump is pumping oil. If anyone has an oil pressure light that blinks on and off or stays on at idle the fix is the 72 & up spring against the ball this creates a lil more pressure to the channel that the oil flows to the sending unit. As long as your light isn't on you have oil flowing. Done Deal NO worries drive the hell out of them. LOL
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Re: K Models oil pump mystery

Postby 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?
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Re: K Models oil pump mystery

Postby Lisa » Wed Nov 18, 2020 9:12 pm

All 16 tooth oil pumps had the same feed gears 52-61 72 -76 only difference was in the return gears different sizes = thickness the pressure against the ball or valve depends on oil flow if the light is out it is flowing fine If it flickers tension against the ball isn't enough as the oil thins out and pressure drops because of this. No matter what oil is going to flow by the ball to the motor and feed it enough to be correct for lubrication. Again K and ironhead motors are a wet flow system not a pressure system. Don't forget the 62 to 71 pumps had 14 tooth feed gears and they were fine just wet sumped like all the rest until i got a hold of them. LOL Took care of 3 R pumps also. Done Deal
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