Topic: CB750K tach cable leak

[zabzob]

A leak! At the tach cable. Replace the seal you say? Already did. It's still leaking oil out. In fact it might also be letting water into the valve cover... I'm getting some foaming in the oil tank.

I think the problem might be the cable end itself. The end that goes into the valve cover looks like it is made from a mold with two halves which were not properly lined up, as in the illustration below. I don't know if this is an aftermarket or OEM part; it was on the bike when I got it. PO had sealed it with silicone.

Can anyone comment on whether or not this is typical of a tach cable? Should it be totally flat?

[Gordon]

The end of the cable is not what seals the hole, that's the job of the oil seal.  If you have a leak it's either a bad seal or the surface that the seal sits on is screwed up. 

[zabzob]

Ah, so in theory even with no tach cable installed it should not leak? Maybe I've got it installed wrong. Which side faces the valve cover and which side faces out?

[jawntybull]

I know this post is a bit old but I have the same problem - just installed a new oil seal and its still leaking oil, about one drip every few seconds, from the small gap around the outside of the tacho cable insert where it sits in the valve cover. I'm going to try and put some pipe tape around the tacho cable; any other suggestions? Maybe I'm up for a new cable but I don't want to spend $ on one if it won't fix the problem.

[dhall57]

I had to replace this seal on both my CB750 KO and CB750 K6 neither have leaked since. Did you install it correctly. The side with the deep round cuts goes in first. I use a deep well socket thats just a little smaller than the hole and than gently tap the seal in with a small rubber mallet and do this until it want go any further. Both times I've used the seal for early DOHC 750 it is suppose to be a hair larger so it seals better Honda part#91256-425-003. The # for the SOHC seal is 91256-096-651. Hope this will help.

dhall

[jawntybull]

Thanks for that - you might have solved my problem. I pushed the seal in with the tacho cable, thinking it would push it all the way in. If it needs to go in further then that would explain my problem. I'll pull the cable out and try tapping it in with a piece of tubing.
I think its in the right way - one side was essentially flat and the other side had two rings, one that appeared to fit snug on the rotating spigot and the other around the outside diameter. I put the seal in with these rings facing inwards.

[Gordon]

Tap it in with a socket that just fits inside the housing.  If memory serves me a 10mm fits perfectly. 

[jawntybull]

Yup - problem solved - needed to be tapped in about 5mm further. Thanks!

[dhall57]

Great, glad you got it fixed