Tach repair

[oldman prof]

Is it possible to repair a tach,the electronic parts look replaceable,and what is the most common prob with them,I have a special 81 I think,I have power to the connector(brown,white,black)and all the lights etc. work fine,if it's shot will any 4cyl electronic tach work on this machine,because I hav'nt found a working origanal here in Cape Town (yet).
Thanx
Anthony

[trbig]

Not sure about your bike, but when mine isn't charging and either the stator or the regulator/rectifier aren't working, the tach won't work. Are you sure it's charging? A volt meter at the battery will tell you. If it's getting 14+ volts at 2k RPM or higher, then it's ok and you can start tracking it down. If it's not... then you need to track down the culprit.

I think,I have power to the connector

That's the part that makes me wonder.. lol. Good luck.


Tod

[boyat68]

oldman prof:

Looking at the schematic in the 1979-80 manual, It looks like the tachometer is a simple d'Arsonval movement (moving coil galvanometer) similar to the needle multi meter checker. The brown lead from the Tach goes to the 12V DC siginal fuse 20A, the black lead goes to the ground connection and the white lead goes to one of the three stator leads of the AC generator.

Trouble shooting notes from the manual.

Remove the Headlight Rim
Turn the ignition switch to "ON"

Inside the headlight shell disconnect the tachometer leads from the main harness. Using a pocket meter (multi meter) set the meter to DC 20V

Connect the meter between the white and black wires of the main harness. Meter should show 5~7 volts AC with engine running. Less would indicate an open circuit between the main harness and the AC Gen.

connect Brown and Black should show battery voltage (12V) , less would indicate weak connection or open between the fuse and the main harness.

It is possible that the movement of the tach is faulty, but I doubt it since these movements have a long life and are very robust., I would suspect a corroded connection or a broken connection.

[mro]

Hi Anthony

So...
you actually getting to ride that beast now?


mro

boyat68 pretty much nailed the trouble shooting.
I've run into a FUBARed tac a couple times, but others were just a bad connection. Currently have one that likes to jump around.
May need to open that one for a fix...

[oldman prof]

Yes I' m riding her already,I have got all the power where it needs to be, I have connected another tach so I know the feed is ok, my wife and I had it out on the Cape town toyrun and now I,m going to do some serious work on her(the bike ,the bike)and I took the tach apart because it had been opened and I'm no expert but it does look repairable so I was just wondering if there were any "common" problems so to speak,I just thought I may be lucky.I will post some pics when I repair and spray the frame.

Thanx
Anthony

[webbcraft2150]

Can't help ya much on troubleshooting the tach but I do have a tach and speedo off a '79 special in my box-o-parts. I ride a standard so they are not doing me much good. Don't know if they will interchange with a '81 but I am sure the "special" people here will chime in quick. Speedo is in MPH not KPH so you might be SOL if your is KPH. RPM is RPM no matter what side of the road you drive on. Having MPH instead of KPH could make you VIP on your XS.

Geez, I gotta go, its time for my meds.

[TopCatGr58]

Hey Anthony,

I don't know of anybody who has actually taken the moving parts apart and fixed them, sounds like Boyat 68 knows quite a bit about them!?

As for an aftermarket tach, it won't work using the tach lead because as has been stated it comes off of the ALT, not the engine ignition coil! The other tachs usually use a signal from the negative side of the coils, but ours has a wasted spark system.

I had done the brain work some time back but have since forgotten, but I think you need a tach with settings for 4 and 2 cylinders, and it needs to be on the 2 cylinder mode due to the # of spark impulses it will count per engine revs! With our wasted spark, the coil fires EVERY rpm.
T.C.

[oldman prof]

Thanx guys but a friend phoned me last night late with the good news that he found one for me but I have one more question,I have seen a full list of all the final drive ratios somewere and did make a copy but can't find it and don't know were I found them,can somebody please help.
Thanx in advance.
Anthony

[morticiaann]

Tach repair

I took my tach apart and found some rubber foam had deteriorated and was resting on the shaft that the needle is on. I sprayed it off with cleaner and put it back together. Radio Shack sells; TV-Tuner/Control Cleaner & Lubricant Model: 64-4315 | Catalog #: 64-4315, that works on the inside of the tach if the needle rusts or gets otherwise stuck. Definately take it apart and fix it. Pry the fascia off and don't break the glass. Either use tape or bend it back into place carefully when you're done.