Topic: Erratic Tachometer

[grumpy56]

Tachometer erratic above about 6/7K on my 76 400/F. Perfect up to that range. Removed tach cable from head and connected it to my drill. Tach is smooth as a whistle at every RPM. I see that there is a tach gear that latches on to another gear (I assume) in the valve cover. Anyone have a pic of this connection? Would like to look at that before I remove valve cover to see what is going on. Thank you.

[carnivorous chicken]

Have you lubed the cable?

[grumpy56]

Yes, cleaned and lubed. Also used the cable with my drill and everything worked well.

[BenelliSEI]

With an external spin (your drill) are you getting up to the 6-7,000 range? If “yes”and it’s running smoothly, replace the cable. It feels OK but is dragging and then springing free and creating the surges at the instrument.

[CycleRanger]

With an external spin (your drill) are you getting up to the 6-7,000 range? If “yes”and it’s running smoothly, replace the cable. It feels OK but is dragging and then springing free and creating the surges at the instrument.

I would agree. Better safe than sorry.
I had a speedo cable on my XS650 with the same symptoms.
It bound up and let go and wrapped the needle all the way around and damaged the gauge.

[grumpy56]

Appreciate the replies. I think the tach cable is OK, but will try a new one before messing around with the drive.

[grumpy56]

Put on a new tach cable, ran it up to 9K or so a couple of times, and everything worked fine. Can't tell that there is anything wrong with the old cable, but must be something. Only strange thing is that the screw holding the cable in at the valve cover was very tight to screw in. Did not experience that with the old cable.

[HondaMan]

Many 'modern' aftermarket cables have almost-correct engine-side mounts. If it is a tad longer between the engine-end of the fitting and that screw's hole. it can make it tight. I file a rounded spot where the screw marks them up for a slightly looser fit-up, like a Honda cable would have had.

[Deltarider]

45 years ago I pulled the inner cables, cleaned them with some kerosene and lubed them with some Keenol Lithium grease. Never had to do it again.

[M 750K6]

Yes, I was always told grease, not the lube you'd use for throttle / clutch cables. But 45 years, presumably many thousands of miles, that's going some. Those cables do a lot of revolutions!

[newday777]

Only strange thing is that the screw holding the cable in at the valve cover was very tight to screw in. Did not experience that with the old cable.

Pull the cable out and compare the screw slot location to the original cable end. Same distance?

Or

Sounds like there might be 2 seals in the cam cover rather than just the 1 there should be, someone may not have removed the original seal thinking it was missing the seal(it may have been leaking oil) and put a new seal over the original.  It has happened before by many an unknown newbie. That will put the slot for the screw in the cable end pushed out past the screw location and bind the screw going in as you have said it is. Do you have a new seal to put in the cam tach drive after you remove the old seal(s)?

[grumpy56]

The replacement cable was well lubed with grease. I compared the old (not sure if it was OEM) with the new one (not OEM) and they appeared the same. Screw went in easily with the old cable, but as indicated above, not this new one. No leaks from this area so I have never replaced the seal. I will removed the cable and see if I can tell where the "bind marks" are. Thank you all.