Topic: What might this mean?.

[Old Moe Toe]

Engine is a 750F2. Started up first time since rebore and new pistons. Oil pressure gauge reads 70 when started up. Took a tappet inspection cover off while running and oil is moving around everywhere inside there.
Oil tank quickly drains the 3.5 liters of new oil into the engine, waiting, waiting, waiting....why does the oil not return to the oil tank?(question 1).
The bike used to do this before re-build.Sumping when sitting, then when you went for a ride for several miles the oil was back in the tank. Was hoping the new return valve rubber in the oil pump,  new seal and 0-rings might have fixed the issue.
Is it bad news to run the engine when there is the right amount of oil it but virtually none in the oil tank? (question 2). There is a very small amount of oil in the oil tank, maybe just enough to neatly touch the dipstick and what is in there is definitely swirling around.

[BenelliSEI]

So if the return stage in the pump is slow to deliver.......
1.Suction screen is plugged?
2. Something not right in that side of the pump?
3. Return oil line collapsed/plugged?
4. Tubing in tank plugged with something?

[Old Moe Toe]

Just been fitted with a new screen, so can rule that out.
How would one check the tubing in the tank?.

[PeWe]

Both my CB750 will empty the tank if started and idling on sidestand. I was lucky to see in time when oil pressure went red on my K2.
Both have renovated pumps and good pressure.
Oil seems not to reach the strainer to be sucked by pump and back to tank.

My K6 was wet sumping from the very beginning. I got used to it and told to be std CB750 behaviour.
Oil always delivered to tank in time to return back to tank, pumped forward to oil pressure sensor and further to filter. over 100.000km done that way.

It has got a restored pump after that, oil stays in tank.
But, will empty tank if idling on sidestand.
A 20 minute ride to ensure actual oil status, if more oil is needed.

[Old Moe Toe]

Both my CB750 will empty the tank if started and idling on sidestand. I was lucky to see in time when oil pressure went red on my K2.
Both have renovated pumps and good pressure.
Oil seems not to reach the strainer to be sucked by pump and back to tank.

My K6 was wet sumping from the very beginning. I got used to it and told to be std CB750 behaviour.
Oil always delivered to tank in time to return back to tank, pumped forward to oil pressure sensor and further to filter. over 100.000km done that way.

It has got a restored pump after that, oil stays in tank.
But, will empty tank if idling on sidestand.
A 20 minute ride to ensure actual oil status, if more oil is needed.

I am glad you said this PeWe. My bike has a side stand only.
Took the bike for a 15 minute ride today and the oil tank was full when I got home.
I am not 100% convinced everything is great though.
The oil pressure gauge reads about 70psi on start up when cold and stays above about 50 when the revs are over 3500, but below that it drops off pretty quickly when hot. In fact when hot the oil pressure gauge almost works like a tacho. Don't remember it doing that before hand.
I had 4 spare oil pumps when I re-built this engine and picked the pump that seemed to be the least worn. I was a bit suspicious of the new leak stopper rubber I fitted as it was not in a Honda type sealed bag and it had to be really pushed hard into the stopper valve to fit properly.

[PeWe]

Really low pressure when hot can be the oil, too thin.
20W-50 motorcycle oil used?
My bikes have closer to 80PSI when started.
I think around 60PSI when cruising in 4000rpm. Seen around 40PSI summertime and ca: 30C ambient temp.

Most important no flickering oil warning at idle. If it does, increase idle to 1200rpm, my favourite idle, easier to ride in the city with not that hard engine brake and easier take-offs.

[Old Moe Toe]

Yes 20w-50 oil.
No flickering oil light but am on alert looking for it and glancing at the oil gauge too much as well. I suppose you get that when you have put a bit of time and money into a re-build.

[PeWe]

My pumps have also new rotors from MessnerMoto. Better pressure when hot.
And, yes extra important after a restore. Before too, avoiding a restore

[newday777]

Where you say you only have a side stand on the bike, get a wheel chock to set the bike upright and see what the results are of your oil in the tank and report back results. This being on the side stand is the most likely your problem along with the fact that you are looking at the level while running. Oil level check is always done on the center stand, per honda manuals, always several minutes after warm up so the oil level settles.

[Old Moe Toe]

Newday, I did have the side stand sitting on a block of wood so that it was not leaning right over.
Am starting to wonder about the oil stopper rubber that I installed. All the ones I have seen are an easy, almost loose fit in the metal valve in which they sit. Not the case with the one I fitted, I had to really force it into the valve.

[BenelliSEI]

“Moe”...... if that anti dumping valve is not seating properly, your oil tank should be almost empty (overnight), before start up. If that’s the case, i’d Be tempted to drain the sump, and pour the oil back in the tank, before you crank it. If the tank is full up, after a longer ride, but then drains overnight, I’d suspect it’s partially stuck open...... That would also mean your losing partial volume and pressure, to oil that is just dumping back to the sump when you are running.

[Old Moe Toe]

Thanks Benelli. Last night the oil stayed in the tank. I started it up again this morning and watched a good portion of it empty, however not enough to go below lower dipstick level. So maybe things are not too bad after all. Perhaps I am a bit paranoid about frying a new motor.
The wildly fluctuating oil pressure gauge still torments me. It gets great pressure 70psi when cold but after say 20klm ride and at lower revs it can drop down to about 20psi. Unsure if this is usual or not?.

[BenelliSEI]

Moe..... my 1971 K1 sucks the oil down the stick, and then shows the tank at top line at rides end, exactly as you described The engine only has a top end rebuild a few years ago, original bottom end, about 24,000 miles total. It exhibits the same pressures you are seeing. When hot, 60-70psi out on the road. 20 psi at idle, sometimes even less.
I think you are just fine....

[HondaMan]

I have experienced more of this situation on the F2/3 than any other 750, probably due to the higher heat of these engines.
The 'tunnel' on the oil pump where the little plunger pushes on that rubber stopper may well be oval. This makes the plunger (Honda called it a 'piston') stick either/both partly open and/or too much closed, negating the action of that nice new rubber seal you took the trouble to install.

I have fixed them several ways: I used to have a nice, extra-fine ball hone of the right size to run in the tunnel at the tight spot for a few seconds (30-90, usually), then polished it smooth with some 1000 and 2000 grit emery paper, wrapped around a slotted dowel and run with a drill. I wore that hone out, though. You can use some of the 2-stone brake hones, if you can find the one (was made in Japan then, probably China now) that wil fit into the tunnel. it's prety small, though. The 'tight' spot is always in the same place, about 3/4" from the end of the rubber seal.

[PeWe]

I grinded that valve too for easy action. I noticed it was almost stuck. Cleaned the hole in pump too.
I guess that some pumps are made that way, wet sumpers.

But, I have seen that tank can have good amount of oil, start bike, idle while I'm sitting on the bike that is not leaning, a short slow ride (5 minutes). Oil level is now much lower than when started. It take a while to fill the tank again. This is only happening at cold starts. Both my bikes.

Highest oil level in tank after a harder ride, 160kmh (100mph) and more. So the pump can keep up to fill tank when pump is really revving taking oil from tank.

[Old Moe Toe]

There is a saying that goes something like, "Most things you worry about never actually happen".
Have decided things are not going to self disintegrate with this motor for the moment.
I did not re-use the oil pump that was on the bike because I could feel that cut out valve was catching in the bore and assumed that was the reason I used to get oil tank draining when not used. I swapped it with one of 5 spare pumps I had that had the smoothest feeling piston/cut out stopper valve and the actual top pump unit with the least clearance in the rotors.
Having a bike that leaked oil, used oil, AND wet sumped was a dangerous combination because you lost track of how much oil was in it. Many times I had checked the oil before a ride, added quite a bit to top up the tank and then during the ride the previously sumped oil had also joined the party in the oil tank and ended up all over the back tire because there was too much oil for the tank.
It's not a good look. Strangely enough it is not as slippery as hitting a patch of oil on the road for some reason.
So far the bike is now not using or leaking oil. A few of the acorn nuts in the head were on the wrong studs (F2 motor), and one of the cam tower bolt holes had been helicoiled out into the world/atmosphere as we know it.
Thank you very much for the feed back.