Topic: Oil at the top end question SOLVED

[cookindaddy]

So I've got my rebuilt 78 750K engine back in the frame with the oil tank and the filter attached with new o-rings, the neutral switch is in the bottom and the drain plugs are in place with new crush washers.

I started to fill the oil tank with fresh 10W40 and was measuring as I added 2.5 liters and then I ran out of oil. It should have 3.5 according to the manual. The oil level in the tank is pretty almost at the fill opening, way over the dipstick full level. I'm thinking that it needs to drain down into the crankcase and it would help if I turned the engine over a bit.

I hook up a 12V power pack with a built in switch to the starter motor leads directly (the headlight bucket wiring isn't finished yet) and I'm cranking and testing each cylinder's compression as I go. All the plugs are out. I have the rear valve tappet covers off so I can watch for the oil that is hopefully going to come gushing out over the lifter arms eventually.

The compression test is pretty good I think:
#1 130 psi
#2 130 psi
#3 110 psi
#4 125 psi

So I've cranked for quite a few minutes in the process of doing these compression tests with pauses as I move the compression gauge between the cylinders. (Its a bear to get my hands in at 2 and 3!)

After maybe 10 minutes of cranking total there are no rivers of oil are coming out over the lifter arms. In fact I can't see *any* new oil at all, just the sheen of what I put on last fall.

By now my power pack needs a recharge and I'm thinking about what to do next. The oil level in the tank looks about where it was when I stopped putting in oil.

Questions:

1) Should I keep cranking tomorrow when the power pack is recharged?

2) Should I measure the resistance at the oil pressure switch terminals to see if it is actuating?

3) Will the oil drain into the crankcase overnight?

4) Does the oil pump need priming somehow?

5) Did I f**k up somehow?

I know about the little teeny o-rings between the jugs and the head and the ones under the towers and I am SURE that they are new and in place correctly.

Thanks for your thoughts.

[Gordon]

I think question #4 is the key.  You probably need to prime the oil pump. 

[Bodi]

The 750 oil pump is actually gravity fed since the oil tank is above it. The 3.5 quarts for a full oil change includes the amount in the sump below the scavenger pump pickup, it's called a dry sump engine but it still has some oil in there.
The pump doesn't move much volume at that speed either, and probably only dribble a bit of oil to the top end.
At cranking speed the engine is turning well below idle RPM, and the pump will take a LONG time to fill the oil filter housing and main gallery before it can push oil up to the head. I would be a bit concerned but not paranoid about the oil pump in your situation.
I would be very concerned about the starter motor though. This is not designed to crank the engine for more than a few seconds at a time. Don't run it for minutes without a rest, I would recommend a 1:10 duty ratio - one minute running and 10 minutes to cool.
I would make sure the tank hoses are connected correctly: if you reverse the feed and return hoses you won't get any oil to the pump (or motor).
If you want to see if the pump has worked at all, loosen the oil filter housing now. The oil from the pump goes directly to the filter, then to the main gallery after filtration. If the housing is dry after 10 minutes of cranking there is some issue with the oil system.
Once you see the hoses are correct and that the pump has delivered at least some oil to the filter housing, if the engine is ready to go... start it up. You should get the oil light off in no more than 5-10 seconds. The tank should empty considerably in the first few minutes of running (as the sump fills up to the scavenger intake), top it up to the full mark. If the tank empties completely you may have a priming problem with the scavenger pump, but trochoidal pumps are generally self-priming especially with the 2 inch or so lift in this engine. You should be able to see oil returning to the tank by looking in the filler hole.
Hopefully you used some assembly lube on the main and cam bearings, but if you oiled them thoroughly before assembly they should be good to go.
That's a good set of compression readings for an engine with new rings. You will get higher readings once they've set in properly.

[cookindaddy]

Thanks, excellent comments all.
I was checking the compression, so didn't run the starter motor for minutes at a time, more like 15 seconds or so and then off for minutes while I switched the compression gage.
I've been reading about how and when to prime the oil pump and will try some of that tomorrow.
Good to have you all here helping me!

[cookindaddy]

Bodi: I've checked that the hoses are routed correctly. The feed from the tank goes to the back fitting on the engine as the manual shows it should. I didn't take the hoses off the tank and it would be impossible I think without switching the hoses to have them wrongly connected? I removed both the hoses from the engine. Oil comes out of the delivery tube from the tank (the rear one). The other is dry.

I pulled off the oil filter housing as you suggested and it is dry. No oil has got there yet.

I also pulled off the drain plug from the sump, but as expected there is no oil there yet since I now understand, it must run through the whole engine to get to the sump.

I also pulled off the plug at the end of the main gallery (above the points housing) and it does not look like any oil has made it into there yet either (as it wouldn't if it hadn't got to the filter).

I did oil everything in the top end well last fall when I put it together but I am concerned about getting it right before trying to start it although I appreciate your confidence!

In reading about priming the oil pump in other threads, I read to put the bike on the side stand and to pour oil into the gallery. It would have to saturate and get through the filter before it reaches the oil pump. Do you think that I should try to do this?

Thanks

[sparty]

After my build it took quite a while until the pump was primed and oil got to the top end.  I did pour some oil in the top end through each tappet opening - 1/2 quart.  In 15 second bursts I hit the starter button and had the galley plug removed.  Eventually oil flowed out to the open galley and I sealed it up.  More bursts and then I had good oil pressure.  It does take some time so be patient.  I also got worried at first.  Plus I have an oil cooler, so it did take longer to build pressure as it filled with oil and the air was removed.  It will work - give it time.

Good luck,
Sparty

[cookindaddy]

Thanks sparty. I did it this way (thanks to kghost in msg "No oil pressure 72 CB750" March 29, 2007, 03:14:53 pm)

Here's what you do.
Pull the spark plugs.
Pull the left gallery plug where the gauge is.
Put a bit of compressed air on the oil tank...I just cover the oil filler with my hand while applying a little compressed air under it.
Spin the engine till oil appears out the galley plug.


It worked great! Then I put the galley plug back in and a few more seconds of cranking and I saw oil coming out around the rocker arms!

The "cover the oil filler with my hand" didn't work for me. I used the rubber mount for one of the headlight side reflectors and a small rubber grommet on my air gun to seal the opening in the rubber mount. This went on over the oil filler opening to seal the air pressure into the tank. It still took about three minutes of air pressure and cranking before I saw oil out of the gallery, but it worked!