low oil pressure

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Apr 15, 2004
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I think I have a problem .

I bought the OldBritts oil pressure gauge kit and installed it last night (very nice kit BTW). Startup pressure looked ok but it seemed low during the test ride although hard to read in the dark.

This morning I went for a longer ride. Pressure was 30 psi while warming the bike up but during the ride it just kept going down. By the end of my 45 min ride I only had 10 psi at 4000 rpm, 5 psi at 3000, and zero at idle. So I guess I won't be riding the bike any more until I can go in and find out what's wrong. :(

One question running through my mind is, how much damage has been done to the engine? I think it's been run with low pressure for years, probably a few thousand miles in all (DPO didn't ride it much). When I did timing side maintenance this winter I found the oil pump output seal was missing. The guy apparently forgot to replace it or maybe he was just too cheap (he had a real aversion to replacing gaskets). It couldn't have had much oil pressure with the seal missing.

After I completed the timing side work all seemed well for a while. The bike could actually sit for two weeks before the oil would drop off the dipstick. That was a big improvement. But that deteriorated as the weather warmed up. Now it wetsumps the entire oil tank in three days. I'm wondering if it's just the warmer weather or if something changed in the motor (maybe the crank seal blew out or ???)

And, as I posted earlier, the right cylinder smokes heavily (looks like rings) and it's got the startup clatter. That's getting worse too. The bike still starts easily and runs well but I can't help feeling it's time for a complete engine teardown. It's pretty disappointing.

Thoughts and opinions welcome...

71/2 750 Roadster,
Well one old trick was to put sawdust in the oil, kept things quite long enough to get rid of the bike :D . That being said as long as oil is getting to the crank then centifugal force will give some pressure at the big ends even if the pressure at the gauge is nil, thats how the DPO got away without the oil pump outout seal, the oil still pumped out and hit the hole in the timing cover and was sucked in by the oil exiting the big ends. However you will have had no pressures at all to the top end which is probably where the rattle is coming from and even if the big ends got oil the pressure was too low. A small strip down to

1. Rebuild the pump (dismantle and then use emery cloth and a piece of plate glass to gewt all the mating surfaces flat and score free with just minimal clearences for the gears)

2. Put a new seal in the timing cover

may get you to the winter but then I would do a full stripdown and rebuild, use the NOC DVD and you will not go wrong, but only rebore if you have to, new rings may be all you need.
Debby, Going through the same rag on an 850 I own. Put on a gage got simular readings. Shimmed the spring on the oil pressure releif valve and it would not produce any difference. I added two .040 washers and because if the non-result stopped right there.
Now this my reliable old beater that I have been thrasing about for four years now with no clatters it runs real well. Your situation is of course different but I am going to ignore it for now it only bugs me not the bike.
Have you tryed adding some washers to the oil presure spring? norbsa
I think the relief valve needs attention too. Last night it went up to 60 psi on startup then the valve opened and the pressure dropped. This morning the gauge shot up to 90 psi before the valve opened. Maybe the valve is sticking? Perhaps a good cleaning would help?

You might find this interesting. It is from the NOC Commando Service Notes by John Hudson, Norton Service manager.

  • "Mention of pressure brings me to another point- fitting of oil pressure gauges. On the Commando an oil pressure gauge is more of a liability than an asset. .... At high speeds and high oil temperature the pressure can drop to nothing on the gauge because the pump can hardly keep up with the rate the stuff is flying out of the big ends. The centrifugal force can keep the pressure at the big ends above the danger point, so there's no real panic- but the gauge would inspire you with horror. ... If you want an interesting gauge to frighten yourself with, but, which is inherently safer and can give useful information, fit an oil temperature gauge in the oil tank. Let me know what it reads as you change in top for the Mountain Mile on both the fourth and fifth lap!"
PO had installed an oil pressure gauge on my 850 before i bought it - 20+ years ago.
It works well most of the time but occassionally the little pixie behind the dial has a day or even week or two off and the readings drop way below normal or even to no reading on occasion. There seems to be no rhyme or reason to it, and no real engine problem that i know of.
I just put it down to Lucas having had some input into the lubrication system anonimously.
On the serious side, when the guage is working i treat it as a guide to when the engine is fully warmed and when the readings are off, and in the absence of any other symptoms, i just ignore it.
Measuring oil pressure at the rocker feed is, as has been said before, a guide, and not much more. If you look at the lubrication system on the Norton, it operates on volume, not pressure. In a babbit bearing engine, the crank, rods, etc. all run on a thin film of oil and we see significant pressure (40-100 psi) regardless of temperature. On the Norton, there are many areas, the rocker feed, the hole in the connecting rod to "cool" the piston tops, etc. which will prevent much pressure from building up.

I went through the same turmoil when I assembled my 850 cafe racer motor, fitted the gauge, and watched the pressure reading start at 80 psi, and drop to about 5 at idle after about an hour. Now, after 6-8 years, it still reads the same. The way I look at it, if there is any pressure reading, I have oil flow. If it drops significantly, I'll investigate a rebuild. If it jumps to 100 psi and stays there, I'll shut it down immediately because something is interrupting the flow.

I would not panic over the readings you are getting. The engine may well be tired and need a rebuild, but this is no sign of imminent destruction.
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