Oil light comes on at low rpm

You will lose some power with a 20w-50 but your engine will be better protected as it's air-cooled.
The service manual for a 1981 kz550 does list 20w-50 as an option.
I would be more worried of running 10w-40 in an air-cooled than running a 20w-50.

wrote:

In my opinion, that oil pump "looks" OK... Small striations in the rotor contact faces are "normal".
However, you will have to verify the measurements set out in the instructions. (See attached pics)
The pump cannot work effectively (create pressure) if clearances are bigger than spec.
 

Hey Howard, thanks for chiming in. I did check the rotor clearances with a feeler gauge, and they were well within the limits listed in the manual.

If the measurements are ok, then it is clear that there is a pressure drop due to increased clearances elsewhere.
The first thing I would then check is if the oil pressure orifice could have been omitted, or incorrectly installed by the previous surgeon! 
I'm not sure what the effect of a hardened / faulty o-ring would be (the "oval" shaped one that surrounds the oil pressure orifice in the cylinder block) but it would seem logical that if oil was bypassing the orifice, the pressure would potentially be reduced.

So you're saying I'll need to take off the cylinder head then. Aside from the orifice O-rings, is there a chance that old/worn out gaskets in the cylinder head and valve cover could be reducing pressure as well? 

And if I have to go in there, is there anything I need to be particularly cautious of before I start pulling apart the motor? I am somewhat mechanically inclined, but I am an amateur when it comes to engines. This is my first bike, and I've only been riding/wrenching for 4 months, so I want to make sure that I don't do more harm than good. And if you think that I'm in over my head, don't feel bad about telling me to give up and go to a shop. 

wrote:

You will lose some power with a 20w-50 but your engine will be better protected as it's air-cooled.
The service manual for a 1981 kz550 does list 20w-50 as an option.
I would be more worried of running 10w-40 in an air-cooled than running a 20w-50.

Mine is an '82, but the oil change section of the supplement says to refer to the main manual, so it appears that I have the same options. Maybe I should give that a try before digging any deeper into the guts of the motor. 

Just take your time putting the oil pump back together.
This isn't an area where you want to mess up.
Measure the clearances of the pump since it's out of the engine and write the measurements down in a notebook.
Take plenty of photos of the areas when you remove the covers. It's nice to have the photos for reference.
Which oil are you using exactly?

 

I have been using Valvoline 10w-40 conventional motorcycle oil.

ok
 

I have a few questions regarding cleaning and reassembly:

1. How do I get the screen out of the oil pump without damaging it? The manual is unclear on this, and it's not obvious by looking at it. And once it's out, how should I go about cleaning it?

2. What is the best way to clean/prepare mating surfaces before re-attaching gaskets and covers? And do I need to use any sort of adhesive on the gaskets or can I keep them dry?

3. Do I need to re-stake the oil pump mounting screws? Or is it enough to use blue Locktite?

4. A few of the dogs on my clutch hub are a little damaged, and the backside appears to be covered in tiny cracks. Does it look bad enough to warrant replacement?

 

The back side of the hub is fine. AFAIK those are just casting marks.
I would clean up any burrs on the dogs and check for cracks. If it's just that one chunk I would think it would be fine. Can someone else chime in on this?
I would also just stake the screws. It's easy and you don't have to worry about how long loctite will survive bathed in hot oil (probably forever, but it'd be pretty bad if not).
I put a thin coating of grease on the gaskets to keep them in place and make it easier to remove them if the covers come off again anytime soon (a tip I got from someone on here...)

The damage to the dogs actually occurred as I was removing the hub nut. I got one of those clutch holder tools (looks like vice grips with perpendicular jaws that clamp between the dogs,) and the video I watched on how to use it said not to clamp it too tight, since the hub is fragile. So I kept it a little on the looser side, and as I tried to torque off the nut with a ratchet + pipe extension, the holder tool slipped out of place, chipped a dog, and scraped another. Pretty disappointing. I tightened it up a bit and it worked okay on the second try. I'm a little nervous to use that tool again though.

Anyone know of an easier/less destructive way of keeping the hub still while I tighten up the nut?

No eBay APP ID and/or Cert ID defined in Kunena configurationEBC makes a clutch holder tool, but I've never actually used it.



eBay.com/itm/194382294660

That looks like it would work wayyy better than what I've been using. Think I'll give it a try!

Running a thicker oil (in order to investigate the cause of low oil pressure) is, by far, much less risky than the "open heart surgery" that is involved in removing the cylinder-head.
 Consider that, at the very least, you will need to replace the head gasket and oil-orifice o-ring.
And, while you are in there, you might as well lap the valve seats and replace the valve-stem seals, which will require re-setting valve clearances.
A couple of new, (thinner) shims will almost certainly be required after lapping the valves.
Also, while  open, you could measure the clearance of the camshaft bearing journals with "plastigauge"
plastigauge.co.uk/about/how-plastigauge-works/  

A lot to consider....

PS
While the statement "a loss of power" using thicker oil is technically 100٪ true, I don't think your (or my) butt-dyno would be able to detect it... in my opinion.