Topic: CB750 K2: Where is my oil going?

[Davez134]

1972 CB750K2, 4000 miles on rebuilt engine. I have no signs of oil leaking or fouling plugs, no smoke from exhaust, great compression, running great. Oil lever after oil change about 1800 miles ago was at or near full line when checked after a ride. It has seemed to slowly been decreasing over time to where last week it was about 5/8 to top of full line.

I have also started seeing that when I start the bike from cold pressure is great on my gauge, just about 76psi. I start riding, then at the first stop sign about 2 miles away, when the rpms drop as I'm coming to a stop, my oil light comes on, gauge drops below 5 but goes back up as soon as I rev up. ( this does not happen at all when fully warm) It did it again today on startup, and when I looked in my tank, it was almost empty. I could see the oil going through the return tube at the bottom of tank.

The oil pressure is good when riding, right at about rpm's/100. I rebuilt pump, replacing every seal and o-ring, checked rotor clearances too when I rebuilt motor. Oil is 20w50 conventional motorcycle oil. Where the heck is my oil going? Am I just wet sumping? I feel like I may have been rambling, so if clarification is needed, please ask! Thanks!

Edit: I can add videos too if needed.

[Retro Rocket]

Did you put a kit in the oil pump during your rebuild ?  Sounds like the oil is just leaking through the valve in the pump and sitting in the sump...

[Davez134]

Did you put a kit in the oil pump during your rebuild ?  Sounds like the oil is just leaking through the valve in the pump and sitting in the sump...

Yes, I did. I even tried another just in case about 1000 miles ago just in case of a bad one, buy symptoms are back. I have another pump I may try if I can't figure anything else out.

[scottly]

What is the level in the tank immediately after riding the bike? If it has wet-sumped, it will take a while to pump the oil back into the tank, like 5-10 miles. If the tank drains overnight from full to empty, the oil stopper valve in the oil pump is leaking excessively, but if it takes a month to wet sump, it may be normal, at least for a 40 year old valve.

[Davez134]

Stopper valve is new from Elan. I've been checking right after a ride. Seems to be slowly decreasing as mileage between oil changes increases. I ride the bike to work daily.

[scottly]

Well, if you want to confirm/rule out wet sumping, pull the sump plug and see how much oil comes out; if the 3 quarts missing from the tank pours out, you have your answer.

[Davez134]

Doing that in the morning I post any results. I just finished replacing my transmission in my Lexus, so I'm not in the mood to hold a wrench in my hand for a little bit!

[scottly]

Ouch, don't blame you for being burned out on wrenching after a trans install!!

[Davez134]

Yeah, it must be wet sumping again. I checked immediately after a ride this morning, and it was about half full. Went out and checked just now (about 90 minutes later) and the tank is almost empty. Now for opinions...The only place the oil can flow back out of the tank to the motor is past the oil stopper valve right? I was sent a new stopper valve about 6 months or so ago because this was happening. It seemed to fix the problem for a while, but now its back.

I have another pump (in pieces) and I'm wondering...since I have great oil pressure,  if the only place oil can leak back down from is past the stopper seal, should I just swap out the bottom of my pumps (the part that contains the stopper seal and relief valve) and see what happens? Is there anywhere else I can be leaking down from? Ive looked at numerous oil flow diagrams but I cant figure out anywhere else.

[Davez134]

And, an update...I drained the oil pan through the drain bolt, got 1 quart out of there. Oil level in tank in the oil tank is just barely touching the dipstick, I'd say about 1/4". I was expecting more from the pan (if I'm wet sumping) if oil level was to the top of dipstick when I did my oil change.

[HondaMan]

I went thru this same thing on a rebuild (and then it happened to mine!) after I installed an Elan kit it turned out that the seat where the seal sits in the pump had a tiny nick in one of them, so even the new seal could not hold it back. New pump body fixed that one...the other: the tunnel where the pistons that holds that seal slides back & forth may be warped slightly, as some of them do. One way to solve it is just another pump, the other way is to (severely) clean the piston and polish it, then reinstall the seal (that fixed mine) because this slightly reduces the little pistons' diameter. I don't know what that [tunnel] bore size should be, nor do I have a reamer that size, so I haven't tried solving it that way (yet)?

[scottly]

You may be using more oil than you think, along with a wet sumping issue. My K1 motor uses oil, but not always at the same rate. IIRC, I burned about 1/4-1/3 quart of oil in 800+ miles during the '13 relay? I suspect it's due to the exhaust guides with no seals, as there is no evidence of oil ash on the spark plugs, even though it sometimes smokes out the exhaust.

[Davez134]

I went thru this same thing on a rebuild (and then it happened to mine!) after I installed an Elan kit it turned out that the seat where the seal sits in the pump had a tiny nick in one of them, so even the new seal could not hold it back. New pump body fixed that one...the other: the tunnel where the pistons that holds that seal slides back & forth may be warped slightly, as some of them do. One way to solve it is just another pump, the other way is to (severely) clean the piston and polish it, then reinstall the seal (that fixed mine) because this slightly reduces the little pistons' diameter. I don't know what that [tunnel] bore size should be, nor do I have a reamer that size, so I haven't tried solving it that way (yet)?

I think I'll order a new gasket for the pump (the rectangle one that goes between the pump halves) and try the bottom part from another clean pump I have disassembled. See if that fixes the wet sumping issue. I am more worried about the engine using oil though

[Davez134]

You may be using more oil than you think, along with a wet sumping issue. My K1 motor uses oil, but not always at the same rate. IIRC, I burned about 1/4-1/3 quart of oil in 800+ miles during the '13 relay? I suspect it's due to the exhaust guides with no seals, as there is no evidence of oil ash on the spark plugs, even though it sometimes smokes out the exhaust.

Interesting. I have no idea what oil ash would look like. So, my plugs are not obviously oil fouled but there is one thing I have always wondered about. I have my bike running great so the plugs are a nice tan color through all ranges, but on half of each plug insulator, there is a dark section. Is this what oil ash, or evidence of oil past exhaust guides would look like? I have never noticed any smoking from the exhaust. I will go and take a picture as soon as i can. My head was rebuilt by JMR, not sure if it had exhaust guide seals. The head I sent in was roached so he used one he had already, not sure on the year.

Ok here is the picture of my plug. Each one is like this, a definitive line where one side is darker: I had to play with the light to see it in the picture...

[scottly]

Interesting. I have no idea what oil ash would look like. So, my plugs are not obviously oil fouled but there is one thing I have always wondered about. I have my bike running great so the plugs are a nice tan color through all ranges, but on half of each plug insulator, there is a dark section.

Oil ash is a crusty build-up on the plugs. The dark section you are seeing is normal, due to "shrouding", where the side of insulator isn't exposed to the flame directly.
I doubt there are valve guide issues if Mike did your head.

[scottly]

I checked immediately after a ride this morning, and it was about half full.

Uh, do you mean it looked about half full peering down into the tank, or 1/2 quart low on the dipstick? Even when at the full mark on the stick, the tanks "looks" about half full.

[Davez134]

I checked immediately after a ride this morning, and it was about half full.

Uh, do you mean it looked about half full peering down into the tank, or 1/2 quart low on the dipstick? Even when at the full mark on the stick, the tanks "looks" about half full.

Yeah, I should clarify that. The oil level was about halfway between bottom of dipstick and full mark.

[scottly]

So you used 1/2 quart in 1800 miles, correct?

[Davez134]

Yeah, that's about what it seems like just going by dipstick level.

[scottly]

I would continue to monitor the dipstick level immediately after riding, and keep track of how much oil needs to be added to maintain a "full" reading on the dipstick over a period of miles.

[Davez134]

Will do, as soon as I get this sumping issue fixed

[PeWe]

If oil will not stay in oil tank, so what? NO problem at all. My bike was like that from the very beginning when I bought it 1979. People I knew then told me it was normal. Checked oil when warm to see the correct oil level. After a 10-20 minute ride oil level was true on dipstick.

Oil level started to stay in tank this year after I installed another pump that I fixed with Elan's kit.
 I got a new problem with more oil in tank when changing oil. Tank had about 2L and it fllowed everywhere when it overfilled the 1.5L bottle I used.

Back in the 80's the tank had 1-1.5L,  the rest in the sump. I did not see any problem with oil flowing down the sump when colling down.

[Davez134]

I am not so concerned with oil leaking down into the pan as I am with oil being consumed by the motor. As stated earlier, I have no obvious signs of it, but I'm pretty sure I have "used" 1/2 qt since my last oil change. But, I can't be sure until I can get a consistent oil level in the tank to measure.

[scottly]

If oil will not stay in oil tank, so what? NO problem at all.

It is a problem if the tank is completely empty on start-up; with no oil to supply the pressure pump, you won't have oil pressure until the scavenge pump has moved enough oil from the sump to the tank. 

[Don R]

 A couple things I'm curious about, what is your oil change interval in miles and how much oil do you put in when you change it?