Topic: K6 oil tank swivel fitting leak?

[gearsoup]

Hello all,

After a bunch of life events (all good, just busy) I'm just now getting back to my bike. Over the winter, I noticed a very slight oil leak showing up at the rear wheel. Not a lot, but enough for me to want to fix it before riding again. I assumed that it was the lines themselves who were cracked and leaking (and dripping down the swingarm), so I got some Carpy lines delivered.https://carpyscaferacers.com/shop/shop-our-store/motorcycle-parts-accessories/honda-cb500-cb550-cb750-parts-upgrades/stainless-braided-oil-lines-cb750k-1969-1976-sohc/

Upon disassembly, it appears that it's actually the swivel fitting-to-tank for "Hose A" that is leaking. Doing some reading, some folks say that there's supposed to be an aluminum crush washer in between the fitting face and the oil tank. Neither of my lines have one, and I have no reason to suspect that someone was in their prior (although 49 years is a long time for something like that to have taken place.

Both of the fittings were on there quite snug and the face of "A" (where it mates to the tank) does have some small nicks in it. My first temptation was to get a rubber crush washer (Buna-N) and trim it to fit, but I suspect that I'll get a tongue lashing from you folks for that idea. Next step is to go to NAPA and see if they have a metal crush washer of approximate size that could work.

Looking at CMSNL, it's not listing any such item, so now I'm slightly uncertain as to what I can do to solve this.

And yes, I'll be replacing the 15mm x 2.5 o-rings

I didn't do anything with the oil tank after I bought the bike, outside of doing an oil change. I put a few thousand miles on the bike last year and never saw anything close to a leak, so I'm unsure how something like that developed.

As I understand it, the seal takes place between that face and the tank, and the nut is only there to draw the two faces together.

[gearsoup]

Hose "A" end where it mates to tank:

[gearsoup]

With the tank off and the fittings cleaned (wiped down, lots of crud), installing "B" and going fingertight it looks like the thread is bottomed out on the tank and the hose is still somewhat loose. Curious...

[bryanj]

Arnt there supposed to be crush washers in there

[Alan F.]

@BryanJ that's my thinking.
I took a look and CMSNL and Partzilla both show these crush washers. https://www.cmsnl.com/honda-cb750k6-four-1976-usa_model494/washer-plug-drain-14_9410914000/
But the view angle they chose is the worst possible. And yes they do call it a drain washer, but it is not the size used on this oil tank drain. It's used on hundreds of other models.

I couldn't tell you how they've gone missing, maybe ask someone at Cern?

[CycleRanger]

Yes, there should be aluminum crush washers for those lines.

[gearsoup]

Interesting that both of them were missing from the lines. I made a brass crush washer and got everything installed back up, no leaks 100+ miles later..

There IS a crush washer on the actual tank drain plug, one that's much larger diameter than the plug itself. I've left it on, it's doing the job, but will replace it with a proper sized one at some point this summer.

[bryanj]

Confused dot com

The K6 parts list at cmsnl shows no crush washer

The K2 parts list at cmsnl does show crush washers

Q were the hoses changed so as to not need them ?

[newday777]

I removed the lines off a tank (I bought in a parts lot from a barn in VT) a couple days ago and there were no crush washers or orings in the fittings where the lines were attached to the tank. The fittings and lines were tight.

[M 750K6]

I remember no crush washers on those oil feed lines on my 750K6. There is on the drain plug.

[CycleRanger]

Yeah, sorry, I was remembering the drain plug washer. 
I don't have the K6 parts diagram but the K4-K5 diagrams do not show washers where the hoses connect to the oil tank.

[HondaMan]

Confused dot com

The K6 parts list at cmsnl shows no crush washer

The K2 parts list at cmsnl does show crush washers

Q were the hoses changed so as to not need them ?

Short answer: yes.
The last of the K5 and many of the K6 bikes don't have a crush washer (it is flat aluminum, dead soft, if it is there) in that fitting. This happened when the F0 bike sales fell flat and Honda scrambled to bring out some more K5 and then the K6 bikes: these bikes suddenly needed some more "K" style oil hoses, and the return hose wasn't made anymore (the F bike's is different). The scuttlebutt at the time was that a whole bunch of late K5 and K6 bikes got out with the F fitting on the newly-rush-built return hoses, sans washer, so it wouldn't tighten the face of the hose end to the bottom of the tank when hot.

I have "fixed" 2 of them here at my house with a soft aluminum washer in an assortment kit from O'Reilley Auto, but there is just one of these in the assortment. So, I have a whole bunch of other assorted sealing washers with no home, don't know what they might fit?