Oil in Tachometer

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Jun 14, 2006
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Every 100 miles or so oil creeps into the tach on my 1973 850 Commando. I take the tach off, spray break cleaner in the light socket hole, shake it around, drain it out and it is good for another 100 miles. Is there a way to prevent this? Does the modification that adds an oil seal to the cable drive stop this?

Any ideas are appreciated.
Sealing the tacho drive will cure your problem. I would recommend the mod using a small lip seal. My own preference is to bush the drive housing at the same time as the bore often badly worn or comes with a very poor finish.
As stated...might be the drive is really leaking and the oil gets shot up the cable....but that is indeed a ways to go for the oil...and if the drive really leaks...it will be all over the motor at that location too.

Could also be that you have lubed the cable and didn't leave the last/upper inch or two of the inner part dry when you reassembled it...the oil you lubed the cable inner...whatever it is called....with, will then creep up to the instrument and get into it and screw it up. You should leave the last section of the cable inner dry to avoid this.....
Mine did the same thing last year for the first time ever. Strangely without any sign of oil weeping at the bottom. It just started spraying out of the top cable connection. It makes a horible mess on a white Roadster petrol tank.

I put an oil seal in mine about 20 years ago and had never had a problem since. The seal had in fact gone hard and brittle and a new seal has cured it completely.

I am still puzzled as to why there was no leakage at the drive end and why there was suddenly enough pressure in the cable to pump all the grease out plus quite a volume of oil. It was much more than the sort of dribble that usually occurs on the drive. Maybe once it starts to pump, a siphon effect occurs and it starts drawing oil up ?
No oil leaking out of my tacho yet. It all goes spraying out of the tach drive :shock:

I had the oil seal conversion done but it didn't work for me. Actually I bought a new drive unit that had been converted so I wouldn't have the down time. But the oil spraying was so bad I put the old unit back on, complete with old o-ring. It leaks, but a lot less than the new one. Now I wipe after every ride. I guess that's the best I can do for now.

I've been considering getting an electronic tach...

Perhaps a dumb question...but having oil get all the way up to the tach and spray about...doesn't that kind of point to a heck of a lot of sump pressure? I can see how the tach drive could leak...although...knock on wood...mine has never done so, with over 120 on it and still the original seal. But how/ why could that oil you speak about get so high up the drive cable? The oil that might leak from the tach drive, can only be getting out because it it is getting thrown up in that area by the crank...and leak out, because the seal is bad...or it gets drawn up by the turning motion of the drive worm gear and finds it's way out a bad seal....but to have it push all the way up the drive cable and squirt.....there's got to be some hugh pressure behind that. That isn't being caused by the crank throwing it up there....my guess is Sump pressure.

Now's the time for one and all to tell me my logic is off-track...but I don't think so.
If you've got a good seal on the cable to drive housing joint the oil will work it's way up and only show in the tacho body. This problem will eventually ruin the tacho, so perhaps in the short term, an engineered leak at the housing end might not be a bad thing .
If the lip seal conversion fails early I'm pretty sure the cause will be poor bore tolerancing and or finish in the housing body allowing the tacho drive spindle to wobble about. Installing a bush not only supports the spindle but drops the leak pressure at the other end.
Goodness knows where the pressure comes from other than the crankcase, perhaps a breather check valve might help.
Perhaps the oil is being drawn upward from the windings on the cable, similar to an Archimedes screw-type pump?
Thanks for the great feedback. I will probably have a seal installed this winter.

Perhaps you engineers could help design some testing in the mean time. Could I disconnect the cable and see how much oil comes out the end? Probably need something to retain the inner cable. Then one could run it without the inner cable to see if the Archimedes action was bringing the oil up or if it is the pressure from crankcase.

How's that for a start?
Del, Now this is just too much. Archimedes driving oil into the tach? No testing needed. How about 300 running Commando's this summer up here in Michigan. I have never seen or heard of this. You need to do a compression test because your rings are stuck or your breathers plugged. A leaking seal makes a small mess at the base of the cable that's all. Hows this for a test pull the cable from the case start the bike, does air pump out the opening? There ya go.
Excellent points Norbsa. The engine is a fresh rebuild. I checked the breather and it is free. I removed the tach cable at the engine and ran it for about 10 minutes. Oil eventually filled the hole. There didn't seem to be any pressure I could feel. I also checked the tach drive with a pressure gauge which showed no pressure. The oil in the hole showed no bubbling or movement.

I did come up with another question which may have some bearing on the issue. Which way does the inner cable go in? Does the brass ferrule on the inner cable go at the tach end or the engine end? It looks like it could go in either way. Mine was installed with the brass ferrule at the tach end.

As long as your inner cable is out will you check and let me know if its spiral wound? I'm just curious so don't go out of your way or take your cable apart if it's already back together.



The cable is spiral wound. It also turns in a direction that would tend to lift oil toward the tach.
I'm surprised that the cable rotates in the direction it's wound. This might explain the oil being drawn up into the tach, but I would think the cable would tend to unwind itself under these conditions. Shouldn't the cable rotate in the opposite direction as it's wound in order to stay tight?

Do we have any tach/speedo cable experts out there? Could the problem be that the cable is wound the wrong way? It's unlikely but it seems to fit the phenomenon.

Curiouser and curiouser as Alice would say.

Jason Curtiss said:
Could the problem be that the cable is wound the wrong way? It's unlikely but it seems to fit the phenomenon.

When this thread started I also wondered about that!
So I checked some cable inners (never having experienced this problem myself) and, curiously, they all seem to be wound the 'wrong' way!

Thanks for your feedback and ideas. I appreciate your suggestion about not lubricating the cable too close to the top. Since this problem began I cut way back on lubrication of the inner cable. I either wipe it until it is slightly moist with oil or give it a light spray of WD40. I have avoided lubrication close to the top.

I have not given up on the notion that there is high internal case pressure causing this. My initial checks seem to show that this is not the case but I will do more checking when there is a little warmer weather.
You will get it straightened out...got to be some "reason" why this happens... not all of us have such a problem, so it must mean it is not the norm and is being caused by something being out of wack...but you will get it fixed...I have no doubt..... :wink:
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