Tach Repair?

[Anonymous]

Has any one every taken apart their tach mine doesnt keep up with the Rpms of the bike, but it does move and catches up eventually. So i thought if i cleaned it out it might work better.

1st of i need to know how to get it apart
and then what to do

[Jethro]

You sure it isn't the cable attachement? The cable either has squared off ends or has a tounge that needs to be accurately installed to work correctly. Check these before you open the tach, because it would be rare for the gauge itself to be the cause of a misreading tach. There isn't much to 'em, just a couple of gears and a needle. If the gauge is broken, most likely it wouldn't read anything at all.

[chuckycheese]

Yes

I think Jethro is exactly right!! The cable's probably slipping and when the RPM's level off, the cable slowly catches up. Hope so....'cause that's an easy fix.

[Hotblack]

Of course it's wise to be sure of the cable before opening the tach, but the tack itself CAN be sluggish the way described. I think it probably happens from excessive sitting, the lubricant the spindle rides in can become gummy, making the needle extremely sluggish. Another thing you can try before opening it up is drilling a small hole just behind the bezel right where the rubber cushion will cover it back up, and try working the needle with a long piece of wire, being careful not to scratch the face of the guage. If you really have to open it up there are a couple of ways you can go, you either need to put a bunch of relief cuts in the metal bazel and remove it, or actually saw the face of the guage off, and superglue it back on when you're done. This actually works well, if you search my posts you should be able to find one where I described how I did this. Hopefully and most likely it's just the cable though. Good luck!

[argonsagas]

Checking the lubricant in the cable is the first thing to do. Clean it thoroughly, re-lube and install it. If the problem persists, read on....





Being one of those who was born to be forever curious about how things work, when my tach anticipated Halowe'en festivities acouple of weeks ago and tried to trick me into believing the engine was REALLY hitting 17000 RPM in top gear at 50 mph, I knew it was still September, and decided to remove it and find out what was behind this deception.


Taking them apart is really easy, but you do need to be quite careful, or the glass cover will break, and getting it replaced would be more difficult and time-consuming than taking the care to remove it safely.

I used a large pair of multi-fit pliers, the type that has a bent head and can be set to accommodate things of various sizes.

The size is important as bigger sizes have wider jaw faces, and are thus less likely to break the glass, as the pressure is spread over a larger area. The ones I used are 12 inch pliers.

All you do is place one edge of the jaws under the lip of the cover, and the other just short of the glass, squeeze lightly and bend upwards......just a little bit. Move the grip point to either side by a half inch, and repeat....again moving just enough to notice.

Several lifts of this sort around the edge, and the cover will have lifted an 1/8 of an inch or so, and then it can be safely removed.

It appears the most likely thing that can go wrong is the alignment of the magnet drive that makes everything work. When the cable end enters the housing, it is a squeeze fit, and a very poor one, that can come loose over time due to flexing of the cable.

A few parts around the circumference of the sheath end have been bent over a bit, and press against the thin housing to hold everything in place.

Unfortunately, any loosening means the sheath shifts away from centre, and that means the magnet drive mechanism is moved off centre, which directly and immediately affects your readings.

Having this mechanism held firmly in place, and accurately centred, is vital to the performance of the tach. I bought another tach, and it will be installed tomorrow, so I have not attempted repair as yet, but I will report if and when I try it


Small note....if you are going to try opening your own tach, place some tape across the top, to avoid scratching the paint with the metal pliers....and do remember....use only tiny movements.

[Anonymous]

I just had these symptoms myself recently, and then my tach quit working. It was the cable. If yours is like mine, it has a square end where it goes into the tach, and a sleeved end with a slot that goes into the cylinder head. My cable was spinning inside the sleeve and eventually got loose enough to quit working.

My solution was to thoroughly clean the cable and sleeved end piece and re-attach with good old JB Weld. It's been working fine for several hundred miles so far. Certainly cheaper than a new cable. :?

If the lube inside the tach is stiff, a little light oil in the drive cable opening should help.