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Sudden low oil pressure SP250

Ian Slade
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Re: Sudden low oil pressure SP250

Post by Ian Slade »

It's no load, you worry too much.
Owner since the 70's, Genghis is slightly to my left.

Phillmore
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Re: Sudden low oil pressure SP250

Post by Phillmore »

I'd be asking what is floating around in the oil that could have blocked the pressure release valve. May be worth an oil and filter change.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

Christopher Storey
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Re: Sudden low oil pressure SP250

Post by Christopher Storey »

Ian : I am sorry to tell you that no load is just another adverse feature : more catastrophic engine failures occur under no load or overrun conditions than at any other time . I think, but can offer no proof , that this is because the negative g loading on conrods in particularl are at their highest under such conditions

Ian Slade
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Re: Sudden low oil pressure SP250

Post by Ian Slade »

The pressure release valve by passes the filter as it is also a bypass valve, therefore if it sticks open little oil will be filtered, it pays to ensure your sump is kept clean by being very careful when filling or topping up. See page D6 and Fig. D9 in the workshop manual. Should something have jammed the relief valve, perhaps a sump removal and a thorough clean of both the sump, scavenge filter and pipework would be a prudent exercise.
It was a well known fact that cars leaving the production line were revved to the max rpm, diesel engines are more prone to failure during this process than petrol engines. Negative G ? do you mean the conrod is under tension due to the piston drag as it drops on the inlet stroke or compressed under the compression/ ignition stroke or even less so on the exhaust stroke?
Owner since the 70's, Genghis is slightly to my left.

Christopher Storey
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Re: Sudden low oil pressure SP250

Post by Christopher Storey »

Ian : the negative g is during the deceleration phase of the upward strokes. It is resisted considerably by compression when under load, but there is little resistance when under no load, and the same applies to the exhaust stroke. It's a long time since I could trot out the equations, but IIRC with most engines there was something like 2000g negative applied during the deceleration phase.

I think your reference to engines being revved to maximum is correct, but you seem to be under the impression that this was with no load. That is incorrect : all the Jaguar production were run for several hours on coal gas on a dynamometer before installation, and at the end of the process a flash bhp reading was taken , but this was, of course, under full load on the dynamometer

Ian Slade
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Re: Sudden low oil pressure SP250

Post by Ian Slade »

Jaguar, may be, but not Fords etc, they either passed or were shoved by the wayside for later attention if anything untoward was noticed. Regarding negative G in an engine, it wasn't a problem in the 1960's the conrod was either under compression or tension, negative G only came in with the space age, used to be called centripetal force. The odd quick rev to 6K on the SP engine won't hurt if not done repetitively, though the worry of where the bit that jammed the relief valve went may well hurt. Problem is the cost of finding it, or clearing it may well cost the same as hoping for the best and not getting it.
Owner since the 70's, Genghis is slightly to my left.

Fossil
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Re: Sudden low oil pressure SP250

Post by Fossil »

I think that the advice to remove and clean the sump thouroughly applies not only in this situation but to any engine sump that has not been removed at some point within the past couple of decades. Every Daimler sump I've ever removed, genuinely, has had a layer of thick hard dark grey sediment covering the bottom at least one half inch thick, which has had to be scraped off with my trusty stainless steel artist's palette knife, (probably the most valuable engine tool I have and the one I mislay most often).

I've no idea what the sludge comprises, I assume some sort of carbon based combustion by-product that has not been filtered out. Fortunately I've never found any metal fragments or bits of silicone seal in it. At any rate this is what I've found in at least two Conquest, two 2.5 V8 and two 4.5 V8 sumps within the past 30 years. Fortunately later Conquest engines have a steel basechamber so that the entire alloy structure doesn't need to come off. I sleep better at night knowing that it has been thoroughly removed.

Cheers

Geoff

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