Topic: CB750 K2: Where is my oil going?

[Davez134]

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?

I changed it at 100 miles after complete rebuild, then 500(I think), 1000. I changed it at about 2000 because I dropped pan to replace oil stopper seal. Bike has 4,000 on it now, was probably going to do 2500 mile intervals since it gets so hot here. Each time I drained tank, then pan, then filter housing, replaced with filling tank with about 3 quarts, going on a ride, then maybe a bit more until level was at full line with bike on center stand.

[Davez134]

Interesting, the scavenge side rotors are out of spec when measuring clearance. Pump side is still good. Oil stopper is soft and appears undamaged.

[Davez134]

CycleX sells "reconditioned" pumps now, so I got one to try out.




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[Davez134]

Update...installed the new oil pump, about 100 miles on it so far. Great oil pressure cold and warm. Pressure does not drop off at idle anymore (level in tank is staying constantly above minimum, therefore getting to pump all the time) It's looking like the scavenge side of the pump, as well as the seat and walls of the oil stopper area were worn. Anyway, all seems better for now, just have to keep an eye on tank leaven for the next 1500 miles or so and see if there is any oil consumption.

[HondaMan]

Update...installed the new oil pump, about 100 miles on it so far. Great oil pressure cold and warm. Pressure does not drop off at idle anymore (level in tank is staying constantly above minimum, therefore getting to pump all the time) It's looking like the scavenge side of the pump, as well as the seat and walls of the oil stopper area were worn. Anyway, all seems better for now, just have to keep an eye on tank leaven for the next 1500 miles or so and see if there is any oil consumption.

That's a nice-looking pump body! I wonder if they had it vapor-blasted?
You can usually skim the body of the pump and/or cover a few thousandths of an inch to bump the oil PSI and flow back up, if the pumps are worn a lot. The 2 places I usually see the wear affect operation is in the leaking-when-parked mode (oil stopper situation) or else the low-PSI-at-hot-idle situation. The latter was the issue on my own, at 140k miles, that nudged me to change mine to something newer, but after I took apart my old one I am thinking of skimming the covers and maybe reinstalling it to see how it goes. The rotors in mine are not bad at all, just one scratch on the hi-PSI side, but the clearance between the sides and the cover were pretty big, more than 0.023" IIRC. It still reached 55 PSI at 2000 RPM easily, though. If I sat in traffic on a REAL hot summer day for more than, say, 60 seconds, I could hear the lifters starting to get noisy at idle, and raising the speed to about 1200 RPM would quiet them back down after a couple of seconds.

[Davez134]

Update...installed the new oil pump, about 100 miles on it so far. Great oil pressure cold and warm. Pressure does not drop off at idle anymore (level in tank is staying constantly above minimum, therefore getting to pump all the time) It's looking like the scavenge side of the pump, as well as the seat and walls of the oil stopper area were worn. Anyway, all seems better for now, just have to keep an eye on tank leaven for the next 1500 miles or so and see if there is any oil consumption.

That's a nice-looking pump body! I wonder if they had it vapor-blasted?
You can usually skim the body of the pump and/or cover a few thousandths of an inch to bump the oil PSI and flow back up, if the pumps are worn a lot. The 2 places I usually see the wear affect operation is in the leaking-when-parked mode (oil stopper situation) or else the low-PSI-at-hot-idle situation. The latter was the issue on my own, at 140k miles, that nudged me to change mine to something newer, but after I took apart my old one I am thinking of skimming the covers and maybe reinstalling it to see how it goes. The rotors in mine are not bad at all, just one scratch on the hi-PSI side, but the clearance between the sides and the cover were pretty big, more than 0.023" IIRC. It still reached 55 PSI at 2000 RPM easily, though. If I sat in traffic on a REAL hot summer day for more than, say, 60 seconds, I could hear the lifters starting to get noisy at idle, and raising the speed to about 1200 RPM would quiet them back down after a couple of seconds.

High psi side was good, 60+ psi while cruising when fully warm (gets hot out here too!) pressure at idle was just about 12-13, but it would drop off and light would come on if I got stuck at a light,  then go away as I revved it up. This lead me to believe the scavenge side was out of spec. I witnessed it for myself, as I looked in the oil tank while the bike was idling and saw the level drop to the point that I could see oil going into the drain tube to the high psi side.

[754]

The pump body looks like it went thru a vibratory tumbler or wheelabrater..

[Davez134]

The pump body looks like it went thru a vibratory tumbler or wheelabrater..

Well, however they clean them up, it works great. And hopefully these pictures are the only time I will ever look at that pump again

[Davez134]

Bringing this up again. It has been about 1500 miles since my last oil change. After my 20 mile ride home today, I checked the level on the dipstick. It was about 1/3 of the way to the top of the crosshatch marks. I drained the tank, sump, filter, and I only got 2 quarts out. I know I had 3.8 quarts in there. My bike is not smoking, the engine is clean on the outside and under with no signs of leaks. Where the heck is my oil going??

[PeWe]

Bringing this up again. It has been about 1500 miles since my last oil change. After my 20 mile ride home today, I checked the level on the dipstick. It was about 1/3 of the way to the top of the crosshatch marks. I drained the tank, sump, filter, and I only got 2 quarts out. I know I had 3.8 quarts in there. My bike is not smoking, the engine is clean on the outside and under with no signs of leaks. Where the heck is my oil going??

Old thread....
- Davez134, did you solve your oil level worries?

My K6 keep the oil level in tank over night, week.....
Oil level OK on dipstick. 
BUT, after starting it when cold the oil is quickly drained into the engine like scavenge pump is not refilling the tank fast enough. A few minutes later the oil level is under the dipstick during 3-10 minutes.
Continue to ride around 20 minutes oil is soon back to full or 3/4 and will stay like that.
No oil pressure warnings.
Oil pump is restored with Elan's kit. Engine has an additional breather hose that might help the oil to flow easier into engine with less back pressure.

I have thoughts about removing pan and inspect the strainer on pump. (was fine about 6000km ago). Pump catch up after a while so it can't be blocked.
-Anyone else seen similar behaviour?
Oil level in tank OK before cold start. Level sinks quickly at start-up (choke idle around 2000-3000 rpm). 10-20 minute ride to get oil up to the dipstick OK area.

My old pump wet sumped during the night. Oil level in tank sank under dipstick or bottom of it, oil level OK after 20 minute ride. This worked fine for 100.000km without oil pressure issues.

[SalNYC750]

hey fellaz any resolution to this one? My dipstick shows only 1/4 full after 10 minutes of warm up then almost beyond full after a 20 minute ride?

...just put in 3 quarts fresh oil change! why would it fluctuate like that??? 

[PeWe]

This is typical for a CB750. They work like that Important to not overfill.
I refill around 2.6L at an oil change.

I have worried about tank getting too low level the short time before it fills the tank and pump running dry. it has not happened yet.

[HondaMan]

hey fellaz any resolution to this one? My dipstick shows only 1/4 full after 10 minutes of warm up then almost beyond full after a 20 minute ride?

...just put in 3 quarts fresh oil change! why would it fluctuate like that??? 

In many of these 750s at their age, the stopper valve in the oil pump weeps a little bit. Then, when the engine is hot, it lets some of the tank drain into the pan until the oil cools off and thickens up a bit, then it stops (until next time). In a severe situation, the whole oil tank can drain into the oil pan! You can replace the stopper valve (it's a little round rubber plug). Both member Elan and PartsNmore sell the kit these days.

After the oil has drained into the pan, and the oil is changed without draining the pan (maybe because a 4-1 pipe header blocks removal of the oil pan plug?) by changing just the oil in the tank, the final oil level in the tank often rises a little because the volumes are 'off' a little bit. If the level gets above 4.7 quarts (CB750K1-K6 models, or 4.2 quarts in post-1975 versions with the plastic dipstick)) it can start blowing out the oil tank overflow tube, making a mess and lubing the rear tire!