Topic: Low oil pressure?

[TerryK]

I finally took my CB550 project bike on a bit longer highway ride (about 120 miles total) and it ran flawlessly at a sustained 60mph. However about 10 miles from home as we were slowed to about 40 and at low rpms the oil light came on. I stopped immediately to check the oil and it was fine and the valve train was as quiet as normal. Let the bike cool way down then restarted and it was fine, no light. Made it all the way home but as I pulled into the driveway the light came on again. My question is, do these engines tend to do this when the oil is hot or do I have an oil pump on its way out?

[Rgconner]

Not on the way out per we, but maybe needs some attention.

There is a post about how to replace the oil pump o rings, that will give it a new life.

Also, what oil are u running?

[Rgconner]

http://forums.sohc4.net/index.php?topic=78643.0

You might want to browse the tips and tricks forums, lots of good info there!

[bollingball]

I would at the very least put a gauge on it. It could be a bad sensor or dirty wire on the sensor. Then do the other things mentioned by Rg.

Ken

[CrankyOldGuy]

When I took my oil pump out of my 750K1, after 40+ years the oil pump o-rings were squished flat. Most likely oil was seeping past the flattened o-rings.  I replaced them with new ones.  I got mine from my local Honda dealer.

Harry O

[bollingball]

On a hot engine with 20w50 oil at 2500 RPM you shoud have about 65 PSI. I agree with changing the o-rings in the pump but there is one more I think it is under the shifter cover you will have to find out the one it is.

Ken

[Rgconner]

Yep.

All are identified in the link I provided.

[TerryK]

Thanks gentlemen! I figured I was going to tear into anyway but I was curious why it just started losing oil pressure in one afternoon verses over a long time period. I'll let you know how I make out.

[dave500]

id say the sender unit is faulty.

[TerryK]

id say the sender unit is faulty.

This is next. I changed the o-rings in the pump and did and oil change and the light still comes on at idle. I have a spare engine that I can rob the sending unit from. Are these units readily available?

[dave500]

its just an on off type switch,take yours into an auto parts store and just match one up,,the actual pressure it switches at isnt really important and most are around 7 psi,its the same part on many cars etc with the simple idiot light.

[TerryK]

its just an on off type switch,take yours into an auto parts store and just match one up,,the actual pressure it switches at isnt really important and most are around 7 psi,its the same part on many cars etc with the simple idiot light.

Thanks Dave. It indeed was the sending unit. Took the one off a spare engine and it works fine. Thanks for all the help fellas.

[thehammer]

I've had the pressure relief valve get stuck on my 75. its the little springloaded slide valve on the oil pump. take the cap off but dont loose the spring behind it. take the spring out and make sure you can easily slide the valve back and forth in its bore. if not hone the bore and clean the valve up with a wire wheel.

might be your issue . . .

[killersoundz]

I've had the pressure relief valve get stuck on my 75. its the little springloaded slide valve on the oil pump. take the cap off but dont loose the spring behind it. take the spring out and make sure you can easily slide the valve back and forth in its bore. if not hone the bore and clean the valve up with a wire wheel.

might be your issue . . .

Can you get to this through the oil pan? Whereabouts? Just the more things I can check while I've got my motor sitting on a bench the better!

[thehammer]

sorry for the late reply . . .
this valve is inside of the oil pump casting wich is under the primary chain cover, right in front of the drive sprocket. the oil pump has a tube that goes down slightly, with a cap on the end of it. take off the chain cover on the engine, then take the cap off the relief valve, again be careful with the little parts, you should be able to move the piston back and forth. if it's stuck, you'll have to take the oil pump off, take the impeller out of the pump and then you will be able to pound the valve out from the inside. use a torch to heat it up a little (but not too hot cause it's aluminum) a propane torch works best or map gas dialed down. then with the oil pump in a vise pound the valve out and clean the valve and the bore with wire brushes, oil and reassemble.

[dave500]

if you need to pound the valve out something is wrong,a magnet should pull it out,,id leave it alone the sender has fixed your lamp issue.

[thehammer]

if it was me i'd pull that cap off and make sure it moves, cause my experience has shown me that this valve is a problem and the aluminum bore expands and contracts when it gets hot and cools down. simply reaming it a little with a wire brush on a drill will allow the valve to move back and forth. like i said, if it moves (or you can take it out with a magnet) great! it's not a problem, but if it's stuck, it could be a big problem for your motor.