Tach stopped working

[Dynamohum]

Riding yesterday I stopped for a break and when I fired it back up, no tach. I’ve never removed the cable before so I don’t know what it’s supposed to look like. Is this broken or notched to fit a certain position? The cable looks ok to me otherwise. If the cable is ok, what could be the reason it doesn’t work?

IMG_2015.jpeg

[tevan]

It looks like a piece broke out of your tach. You need a tach if that is the end that screws into the tach.

[Dynamohum]

No, that end goes in the cam cover.

[tevan]

You have a broken tach gear then. Take the 2 screws out and pull that cover out. Hopefully you didn’t brake the cam holder as well.

[Dynamohum]

Everything looks good except this. Luckily I got the broken piece out as well so I’ll know it’s not floating around somewhere. The gear itself looks ok but the end piece is snapped in two. It looks like it’s pressed in but I suppose I’ll have to get another gear with this piece intact. As I said I’ve never had the cable out to know what it looks like as it fits into the motor. Can you confirm the end of the cable above looks ok like it does, sort of one sided?

IMG_2018.png

[JoeInTUS]

The cable is broken also. It should be “two sided” with a slot for the piece that broke of your drive gear.

[Dynamohum]

Thanks. I thought it must be ‘sandwiched’ but I didn’t recover the lost piece from the cable. The motor has just 41,500 on it and the cable looks lubed, wonder what gave way first or do they go together when they fail? My previous Prolink or my 79 had this issue and they had a combined mileage over 175,000 miles.

[Dynamohum]

I found (one) that is purported to be brand new, part number 12431-422-000 that fits a CBX. Problem is mine looks different. Notice the rod coming from the gear end? Mine is thinner and longer than the new one shown. Whaddyathink?

IMG_2024.png

IMG_2029.png

[Jeff Bennetts]

IMG_6032.jpeg

IMG_6031.jpeg

[daves79x]

So - I pulled the original tach drive out of an '82 CBX I have on the lift. It is exactly like your broken one. Then pulled an original one from the '80 engine I'm building and it is exactly like the NOS one you show in the pic, with the short nose. I pulled the one from my original '79 and it is like the '82 with the long nose. So Honda must have used both styles and called them all 422 part numbers. The one you found will work fine apparently. However, I would pull the valve cover and see if there is any damage to the cam holder. I've never seen these break without someone trying to remove the valve cover without removing the tach drive. Also, you seem to be missing the thrust washer that goes over the cable end of the drive gear.

Dave

[Dynamohum]

I’ve got the washer, just didn’t photograph it. Sure seems odd that both would fit correctly. It’s good that in your experience with cam holders that ‘you’ve never seen these break without someone trying to remove the valve cover without removing the tach drive’ Thanks for the help. Still wondering why it broke.

[daves79x]

I meant that I've never seen the tach drive or the cam holder break on their own. It's doubtful that a frozen cable would break the end off of the drive. But I might replace the tach cable too.

Dave

[Dynamohum]

Yes, new cable and tach gear on its way.