Topic: Really low oil pressure

[AbbyRider]

'77 CB750F - bike was running decent after rebuild, although was very lean. Ran it for two 1/2 hour rides. Oil pressure on gauge (at right side galley) was consistent 60psi while cruising and 20psi or so at idle. Parked bike to adjust fuel/air screws to richen it up a bit. When I started the bike again, oil pressure was near zero while idling, and would only go up to 20psi at full throttle. Opened up one of the tappet covers to see if I could see any oil sloshing around. Wasn't dry, but there was nothing splashing around either.

I drained the oil pan just to have a look at the oil, and was a bit dirty but no pieces of anything. Replaced the 1.4 L that I drained, putting some in through the valve cover and the rest right in through the side oil galley where I have the pressure gauge. Tried starting it, and same thing. Looked into the oil tank and it hadn't gone down at all.

Does this sound like an oil pump issue? I have another oil pump ready to put in if necessary, but am just looking for confirmation that this would be the likely culprit, and that I'm not missing something else that's obvious. Is there someplace else I should look first? Take off supply oil line and make sure oil is getting through?

[70CB750]

The oil pressure gauge is to be trusted?

I can not imagine it go bad, but that's another thing to verify.

When the gauge showed zero, did the oil light come on?  The light pressure sensor is about 7 psi - if it was not on, it contradicts the gauge.

[AbbyRider]

The oil pressure gauge is to be trusted?

I can not imagine it go bad, but that's another thing to verify.

When the gauge showed zero, did the oil light came on?

Good point. I thought about the gauge, but the fact that it had just been working, and the needle is moving to the point where it's registering 20psi with throttle, made me think otherwise. But it's something I will check. I don't have an oil light anymore, as I've stripped out the redundancies.

[70CB750]

I see.

The oil light would be the last thing I would get rid off, but thats just me.   

[AbbyRider]

I still have the pressure switch on there, so it's easy for me to hook up a test light to it. I'll give it a go in a little bit.

[calj737]

For you to allay your fears that you have enough oil pressure based upon a light going on or off, you'd have to know the minimum pressure it sensed before deactivating, right?

I'd remove the gauge, check to see if it has clogged, then reinstall. It's possibly fine particulate has entered the valve while open, and is now preventing it from proper operation. The fact that your oil tank volume hasn't changed would steer my course for pressure remedy.

[AJK]

It does sound a bit like the gauge to me. I wouldn't get stressed about it just yet. As CalJ says, you might have a gauge issue. Do you have access to another gauge to re-try it?

You should put your oil switch a light back in, thats an important redundancy.

If you are seeing oil presence at the rockers then you are probably getting sufficient pressure, however I'd be checking all rockers and also that a gently flow can be detected, so shine your torch through the exhaust side caps and look for flowing oil, even a slight amount of flow is enough to confirm.
 You can confirm this presence of flow by seeing what it looks like with the motor off, then re-compare again with the motor running.

Also just an interesting side note. One thing to be aware of is your side stand length (hence the angle of the bike when parked). My bike has had spurious moments of losing oil pressure and i noticed this when the bike was leaning over quite a bit on the side stand. Once you prop the bike back up, it instantly all comes back. Until i install a longer side stand, i just dont run the bike on the side stand when parked.

[AbbyRider]

Well, while attempting to find the issue, the problem resolved itself, at least for now. Took the gauge off, didn't really see any issue with it. Put it back on, and had same issue. Took #4 exhaust tappet cover off (I had previously taken the intake tappet cover off) and started bike again. Saw oil splashing out. Happened to look down and see that the gauge was once again reading 60psi.

AJK - I did think about the lean, as my kickstand could be a bit longer. But didn't have a chance to test the theory, as everything was working okay by that time.

So... either the gauge has an issue, or something else happened to free things up? I'll just keep watching it closely, and will look at hooking the oil light back up in an unobtrusive manner.

Thanks for the help guys.

[70CB750]

I have a gauge and the light and while the gauge is an important input - I judge how warmed up the engine is by it for instance - the oil light is Stop the engine right now kind of warning. 

If possible, I would put the light back on, since engine without oil locks itself up quickly, that's the most important signal from the engine you are getting.

My $0.02 only 

[calj737]

^^^ that is great advice in my book too.