"....thick oil and the HD studs are causing the oil to get up in the head and is not getting back down to the pump fast enough..."
1.)
This has been up in another thread where one guy had much oil inside valve cover, oil passed thru guides and caused smoke thru the pipes.
That time small oil return holes in head gasket that slowed down the oil flow from top.
Nothing about low level of oil in tank.
Opened up the oil return holes in gasket helped. It was an MLS gasket if I remember correctly and could be used again.
I have drilled my CB750 heads to ensure better flow up to cam. HD studs 8mm thick and holes in head were down to 8.5mm in one head made me to drill the 2 holes for oil up to cam with a 9.5mm drill.
All others 9.0mm.
Ported heads so a few holes on inlet side were a thrill to drill. How much material left? It went well.
This started when one head was tricky to remove. Head nuts had sunken down, pressed the alu around the HD studs very tight.
I had to have a heavy nylon hammer to bang the exhaust spigots to make head free. I let my nearby shop mill all 16 sunken holes so they all were parallel with mating surface and +18mm wide for the washer.
I did not have any oil pressure or sudden low oil level then. Only loose nuts caused oily spark plugs.
2.)
BUT, I have had sudden low oil levels.
I saw level at half on dipstick after ca 25 minutes ride. I thought it will raise.
After another 20 minutes even lower.
I had to return to home, stopping more and more often to see how level just sank. I stopped at a good place made for stops were road had a long pocket. Level had then went under the dipstick.
Called my wife and explained how she could take the car and drive to me. Explained were in the garage she should grab 2 bottles if oil. Spectro HD 20-50 mineral.
I filled tank with both just for sure to have oil all the way home, ca 60km.
I instructed her to watch if bike smoked. I accelerated hard up to 160kmh and throttled off, followed by open throttle. No smoke.
Engine consumed oil so head off. The 5mm valve kit with bronze guides did not last long. The guides had horrible oval holes at top. That head got iron guides and new valves with std valve stems.
3.)
I had after that got a sudden low oil level again. I usually make sure that oil level is at max.
I saw level to be just under half during a ride 40-60 km from home. Level did not raise more so back home where I checked oil level and found it at max.
That happened a few times so I replaced oil pump.
It happened again during a ride I had to interrupt, back home to see level to be max again.
I remembered that I had replaced the oil hoses earlier, just before these low oil level events. Not cheap hoses from CMSNL.
I replaced those and mounted a set of hoses a guy in Germany had made. He fixed a few sets after I had shipped old to him.
My K2 has used them since restore and never had an issue. Over 10.000km then, now +16.000km.
So the new set on. No problem seen so far, 3000km. I swapped the earlier pump back since it was restored with new seals, rotors etc.
So today the thought is oil hoses.
Can oil return hose be too thick?
Interesting to see if oil level can be low again despite some revving.
These events did not trigger low oil pressure lamp.
I have earlier got low pressure, blinking lamp when bike had idled when parked, leaning on side stand.
It happened first on my K2, saw almost no oil in tank.
Added a little more to later see level was too high. Had to remove the same amount I had added.
Later same thing on my K6. Realized that let engine warm up a few minutes parked on side stand is not a good idea.
No problem when let bike stand up.
20W-50 oil is not thick for a CB750. It is designed for it. Air cooled one part of it.
I have read a Porsche forum where use of 10-40 instead of correct 20-50 caused expensive repairs. Too low oil pressure and short lived guides.
I searched for oil temperatures when we had a hot summer. 120*C in tank.
Air cooled Porsche forums must have the answers was my idea.
120*C no problem. Shorter intervals, good synth lives longer than mineral oils.
Modern liquid cooled engines with tighter clearances another thing.
Cars using 0-30 and even thinner!
