Topic: CB750 Wet Sumping

[markjenn]

Hi, I'm having continued issues with my 750K1 draining the external oil tank into the sump.  Over the course of a week or two of sitting, the external oil tank will empty into the sump.  While nothing untoward seems to happen and the tank refills on next startup, I'd like to put it right.

Obviously, something is amiss in the oil stopper check valve area on the oil pump.  I pulled the sump, inspected/cleaned things, and re-assembled but no change in behavior.  My next step is to replace the three o-rings that seal the various input/output connections to the pump (two from the oil tank and the output).  The fiche is below:



On this subject, each connection is showing an "o-ring collar" (#9) and two different sizes of o-rings (#14 - 15X2.5 and 7.2X2.2).  When I had the thing apart, I didn't recall any collars and I don't understand why two different o-rings are specified with no indication as to which is correct. 

Any help appreciated,

- Mark

[markb]

I went through some of that working on my K0 pump.  There should be collars and the large ring is the correct one.  I got small ones at first by ordering by part number and went by the size decription to find the right number for the larger ones.  I believe item #11 is the seal that prevents the oil from draining back into the sump.  I think when the motor is running, oil pushes against it to open a port to the oil tank line and when the motor is off in moves back to seal it off.  Unfortunately it is no longer available and I wasn't able to find one anywhere.  Mine looked OK so Im still using it and it seems fine but it worries me not having a spare.  Anyone know a source?
Mark

[markjenn]

Thanks for reply Mark.  I wonder if the guy that did my engine rebuild a few years back missed the collars - I certainly don't recall them when I was working on the bike, but perhaps I missed them if they stayed with the engine when I dropped the pump assembly down.  I'm going to order the collar and a big o-ring and take it apart again.

Like yours, that stopper rubber (#11), spring, etc. looked fine and the piston (#10) seemed to slide cleanly in the bore.   So I think the valve is doing it's job.

I just recalled (and confirmed) that the Owner's Manual says that if you can see oil in the tank, then you should start the bike and run it a bit before checking the oil level.  This would indicate that perhaps Honda assumes that the oil tank will slowly drain into the sump if left for a long time.  Perhaps a couple weeks to drain down is within normal leakage specs.

- Mark

[bwaller]

You definitely need the dowels to locate those o-rings. I tried unsuccessfully to get a new rubber stopper from Honda so if anyone knows a different source I'd appreciate the news as well.

[Mortum]

I did read somewhere that it was kinda common for the oil to sneak past the check valve into the sump if sitting for a awhile. I Think it was in a manual I have.

[kaysystems]

You definitely need the dowels to locate those o-rings. I tried unsuccessfully to get a new rubber stopper from Honda so if anyone knows a different source I'd appreciate the news as well.

Bought mine from Western Hills Honda last year. Don't know if they have any left.

David

[Clyde]

Wet sumping never used be a problem, but I am hearing of it more and more.
I have recently had a case of wet sumping due to the valve (item 10 in the above diagram) sticking due to a varnish like build up. In this case the bike had been sitting for a long time.
I used some 1000 wet and dry to clean the valve body up and this fixed the problem.

The only other time I have seen wet sumping, was when a bit of gasket lodged under the valve. I don't know how it got past the inlet screen, but it was the problem.

The three collars are necessary to hold the o-rings in place, otherwise they could actually partially block the opening.

At a vintage rally I was told that a person had problems because of a damaged rubber seat (item 11), and as mentioned these are hard to find. The part number is 15166-300-000 and Western Hills have a price of $2.72, but they do not seem to have any stock.

Neither CMS or David Silver Spares  have any available

If anyone can find these rubber valves it would help us, as a lot of these rubber components are now over thirty years old and surely will not survive much longer.

Regds Clyde

[markjenn]

Just to close on my experiences with this, I replaced the three o-rings and my valve seems to be working fine, but I'm still getting a slow drain that will empty the tank in about 10 days or so.  My guess is that I'm getting seepage past the stopper (#11) which is no longer as pliable as it is supposed to be and since they're not available, it's probably something I'll just have to live with.

Good excuse to ride every day or two.

Cheers,

- Mark

Further edit a week later:  Upon further review the leakdown to the sump appears to be much less, perhaps negligible.  I let the bike sit for four days and perhaps it dropped 1/4" on the dipstick, but that might be measurement error.  It's certainly drastically reduced.  So if you're having this issue, certainly replace those 3 o-rings.