Low Oil Pressure

[Kool_Biker]

I have recently completed a nut and bolt restoration of my 35K mile CBX Z engine.
You can see a slide show of the entire operation here:

The entire bike is now complete (but still has a crappy 6:1 exhaust for now) and I have done about 60 sweet miles on it. Finally everything looks, sounds and feels right. The bike starts first push of the starter, idles beautifully and carburation seems (to me at least) 95% there. As I am running her in, max RPM is 4K tops.

The engine is currently on Texaco Magnatec 10W-40 a cheap-ish semi synthetic and I have been experiencing low oil pressure when the bike is at normal operating temperature (a 30 minute ride or so). That is: ~45 PSI (3.1 Bar) @ 4K RPM and ~10 PSI (0.7 Bar) at idle. When cold, indicated pressure is ~75 PSI (5.2 Bar). What more, this pattern has not changed at all. Also when I did the first oil change and removed the sump, everything looked spotless.

Before you ask I have checked the pressure with two concurrently run gauges and they both seem to agree.

Before I look deeper, I will change the engine oil again with a thicker one (Mobil 1 5W-50), check the sump etc. etc. again, and see what happens.
Any suggestions any ideas most welcome - but PLEASE let's not start another thread on oils

Thanks
Aris

[EMS]

The pressure relief valve works against a spring. With age, the spring may lose some of its strength and it may open the relief a little too early. You could also have too much restriction in the oil filter. What filter are you using? Also, where exactly is your presure gauge, Aris? And finally, the oil pump could be bad. Gear and Gerotor pumps wear from day one on and develop internal leakage over time which results in a loss of efficiency.

[Kool_Biker]

Mike:
The oil pump is NOS, sealed in its box.
But I guess the $1000 question here is, is the spring in question serviceable without splitting the engine, i.e. from the sump?

As for the oil filter, I have used a Randakk adaptor with a generic automotive type filter which fits correctly.

The oil pressure gauge is from TIMS and uses an oil gallery plug adaptor on the side behind the block.

P1050881.jpg

Cheers, Aris

[EMS]

If I'm not mistaken, the relief valves for both circuits are integral to the oil pump and should be fine, if the pump is new (unless they are stuck, because of fluid contamination)
The easiest change you could try, so it seems, is changing the oil filter back to stock and see what that does. Fitment was not really my concern. It is more the internal restriction because of the filtration material. The oil flow goes from the pump into the oil filter first. A significant restriction there, would cause a pressure drop behind it.

[Don]

An old time mechanic I trust once gave me a quick primer on pressure vs flow - Lower pressure doesn't necessarily mean the engine internals are getting less oil . . . . but changing to a higher viscosity oil which results in a higher pressure on the gauge probably does. Pressure equals resistance to flow - A higher viscosity liquid shows more pressure because it flows less, all other things equal

Think of a long garden hose hooked up to a 60 psi tap - It flows lots of water and if you had a gauge at the business end, it would probably read 15 psi or less . . . . because there is little restriction to work against, like your new, super clean engine. Now put your thumb over the end and reduce the flow by half and that 15 psi would jump up to a higher number, even though only half as much flow is being delivered. It will only read 60 psi when you have zero flow

True, an engine is different because you have variables. The output of the oil pump isn't a constant number like the 60 psi at the water tap - The engine pressures vary with RPM, oil viscosity, oil temperature and the cleanliness of all the oil passages within the engine - A really complex mix that can change rapidly. Most car manufacturers went away from installing oil pressure gauges in favor of 'idiot lights' because of complaints from owners about what they (mistakenly) think is a 'good number' - My Dad is an excellent example

He had a diesel pick-up which he had always had serviced at the Ford garage - They used Ford branded oil and he had an idle and a freeway oil pressure he was very familiar with. We did an oil change in my garage and I recommended to him that either RPM Delo or Rotella were the diesel oils most trusted by the guys who put millions of miles on the big rigs, so we put Rotella in his truck for the first time since we had added the oil pressure and temp gauges. He drove it for a week or so and was never happy with the new, lower oil pressure readings so he went to the Ford garage and paid more for some of their Ford branded oil and we changed it again. The oil pressure jumped back up to 'normal' . . . . and my neighbor came running over to get Dad's week old Rotella to put in his truck ;)

Personally, I wouldn't worry about your bike at all . . . . certainly not enough to make me want to put some brand of automotive oil in it because you're hoping to raise the indicated pressure on the gauge. Honda didn't give you a gauge because they weren't worried about it and they didn't want you to be either

Don

[barryadam]

Aris,

Some comparative pressures/temps in here (for what it's worth):

viewtopic.php?f=26&t=5550&p=52831&hilit ... ler#p52831

Also, PM sent.

Barry

[Kool_Biker]

The pressure relief valve works against a spring. With age, the spring may lose some of its strength and it may open the relief a little too early. You could also have too much restriction in the oil filter. What filter are you using? Also, where exactly is your presure gauge, Aris? And finally, the oil pump could be bad. Gear and Gerotor pumps wear from day one on and develop internal leakage over time which results in a loss of efficiency.

Mike, on second thought, as I have >70 PSI when the bike is cold, almost from idle, I think the pump is OK.
Indeed the 75 PSI I get, every time, is the relief pressure. I believe the problem, must lie elsewhere.

Earlier on today I changed the oil to the Mobil 1 5W-50 I had already bought and went for a ride, my usual around where i live. Upon my return I noticed the oil pressure at 4K RPM go from the previous 45 PSI to 55 PSI. An improvement, but still below the Honda spec. I did not (yet) reverted back to the standard filter.

On a positive note, the sump plug, sump and filter screen were again very - very clean.

Ah-well, may be I should throw away the oil gauge and just enjoy my bike

Aris

[Larry Zimmer]

Your last sentence says it all, Aris!!

[Kool_Biker]

That last sentence says it all, Aris!!

[NobleHops]

Here's that video of Preston Marks' oil pump test stand, although I very much doubt that this is an issue given the NOS pump.

Just for fun, and because it's cool:



N.

[Kool_Biker]

Absolutely Nils.
And it is not so much that the pump is NOS, BUT when cold (as presumably is the case in the video above), I also have a very healthy 75 PSI, even more than in the case of Preston!
Thanks, Aris