Honda CB125 TD Rev Counter Broken

[ajordan9]

Hi all,

So I just got myself a Honda CB125 TD 1983 model last week with a few little issues I need to work on. Although I don't have much experience with bike maintenance I plan on learning as I go.

So my first issue I plan on tackling is the rev counter. It doesn't seem to want to work! Although the speedometer on the left of it works fine.

I followed the cable from the right hand side rev counter and the cable looks attached and in reasonable condition. But obviously I realise that means nothing.

Do you have any ideas I can start going through?

Thanks,

[jaffa90]

Does the inner cable rotate at both ends?

[ajordan9]

[jaffa90]

Yes, turning the inner cable at one end should turn it the other end, if not then a new cable complete for a tenner.

[Teflon-Mike]

Take off the cable gearbox end, and tacho-end.
Cable should rotate the same amount at both ends if you give one a twist... if it isn't more obviousely snapped and half a cable drops out the sleeve!

Be careful of the primary drive retaining screw; it's often siezed and rounds off easily.

Beneath is the cable drive, which is a very thin brass slot that the cable end slots into the middle of.

Common for numpty mechanics to fit the entire cable this end and push home the outer into the case and expect the inner to find the slot on its own.... seldom does. Consequently the drive goes round and round with the engine and doen't turn the cable; in worse cases the drive can wind up the cable trying to shove it out the way, and either inner cable and or the drive slot can get damaged... In which case you get no taco, or an erratic one.

Only way to tell is to take it off and have a look.

More beware that screw; outer cable has a groove in it where retaining screw should go; if screw chewerd or mangles often not fitted and drive end floats out and as above cable end or drive can easily get mangled. But also common for cable end to be hammered into the housing, in a oner with inner and NOT engage with drive slot, and forcing it damages both, whilst cable end NOT properly seated, and the retaining screw rammed home above or below or ommitted altogether.

In the most dire cases, the tacho takes its drive off a worm gear on the oil-pump; from Snowies Handy-How-To's:

https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/LD07%20Eng%20Build/100_0476.jpg

You can just see it, just there above her hand holding the rubber retainer out the way whilst she removes manky oil strainer.

That worm is metal, and can apply enormouse drive pressure from the 'reduction' it puts on the nylon pinion on the end of the tacho-drive in the primary drive cover.

If the cable is old or kinked and allowed to 'snag', and or primary case badly fitted, then that worm gear will tend to strip teeth off the nylon pinion; and no turn tacho cable.

OR could be in the tacho head.... the spring could be broke.. would tend to send needle round to the red-line and stay there regardless of engine revs... rather than not budge at all, but? Old bike, who knows.

Check obvious easy first, work from there; and snapped cable IS the most likely, obvious and easy to check.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[ajordan9]

[WD Forte]

I've tested this type of tacho by using a cordless drill and a short length of some stiff-ish electrical cable or similar in the chuck.
It should fit snugly into where the cable usually goes

Running the drill anti clockwise as you look at the rear of the tacho should get the needle to move up a bit if the tacho mechanism is OK.
Dont worry the drill wont go fast enough to damage the tacho
its magnetically driven internally anyway

If the needle moves when you do this and cable is Ok then I'd
suspect the problem lies in the worm drive at the end of the camshaft
If it is you may want to live without it unless moneys no problem
____________________
bikers smell of wee

[ajordan9]

[Teflon-Mike]

https://images.cmsnl.com/img/partslists/honda-cb125td-superdream-1982-c-ireland-right-crankcase-cover_big00028371e__0600_9222.gif

Tacho drive is part 3, Should look like two tangs from the top, not a disc. If disc... tangs be broke,

To fit up cable: Slide inner out of outer at the engine end, maybe 3 inch.

slot cable end into drive in the case. make sure properly centered and seated.

Slide outer down inner cable, and bring the retained end down over the drive and into its rebate.

Fit screw... may mean wiggling cable outer bulb up and down a little to line up groove.

that way everything lines up as it should. Try pressing inner and outer into drive hole together, then cable wont always line up with slot, and drive tangs can get bent/broke.

Make sense?
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[WD Forte]

[jaffa90]

Tacho / engine rev counter !
Why bother on a 30 odd year old bike??????

[Teflon-Mike]

[ajordan9]

Hey sorry about the radio silence, busy end to the week.

I think my issue is even after your description of where the tacho/engine side cable goes I cant physically see where it goes! I don't know if im being stupid or not...

So I managed to stick my phone in for a few pics... There genuinely doesn't seem like a 'slot'.

https://ibb.co/kopgeT
https://ibb.co/nMaMeT
https://ibb.co/dHbSKT

This seems to be some kind of spindle, no where to slot anything into. Is that thing right in the middle mean't to be there? The big that is raised right in the middle of the spindle? Or has the old tacho broken off?

The only slot type thing is right on the edge but thats just where the screw seems to go to hold the cable in place.

Thanks!

[Teflon-Mike]

https://cdn.bcf.44bytes.net/files/tach_drv.jpg

Sorry 'slot' is on the cable end; tang is on the engine end. That's what it 'should' look like, and the tang, aght be about 15mm deep or so. (Should also be brassy colour; that one black cos wasn't masked when motor painted)

Looks like yours 'may' be snapped off, and you need new tacho-drive.

What's the cable end look like?
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[jaffa90]

Could it be this cable.
https://www.ebay.co.uk/itm/Tacho-Cable-Honda-CB-125-K5-1972-1975/362053259730?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160727114228%26meid%3Ddf80815d4e634a51801cf69bb9137d38%26pid%3D100290%26rk%3D1%26rkt%3D4%26sd%3D362053259730%26itm%3D362053259730&_trksid=p2060778.c100290.m3507

[Teflon-Mike]

[jaffa90]

I meant the cable ends, the drive has a spade end and the type i posted looks like it will take one.