Replacing Tach Mechanism In Primary Chaincase

[Jimmie]

On my 1967 TR6 650 my tach stoped working. I took the cable off and the tach needle moves when the cable is turned. I looked in the sidecase where it is hooked in while running and the slot is not turning. I need guidance on taking that part off and replacing part(s) so the tach will work. The slotted part turns about 1/2 tun with a screwdriver..back and forth. I assume it rotates when working. Will I need special tools? Any help appreciated. Jimmie

 

[Rocky]

I'm using an electronic tach so am of no help.
Grandpaul is probably the best one to help with this.
He should be along later.

 

[grandpaul]

The thimble on the end of the exhaust cam has 2 teeth that slot into notches on the end of the cam; those teeth can wear down and get sloppy, even break off. I believe they sell a replacement that is able to be swapped without splitting the cases, but I've never installed one.

 

[Jimmie]

The thimble on the end of the exhaust cam has 2 teeth that slot into notches on the end of the cam; those teeth can wear down and get sloppy, even break off. I believe they sell a replacement that is able to be swapped without splitting the cases, but I've never installed one.

Hi GP. I will take the mechanism off and examine it. I will contact Lowbrowcustoms as they have been a big help to me before or maybe another member may reply.Thank you,Jimmie.

 

[grandpaul]

Careful, try removal as a left-handed thread first. Don't strip it out trying it as a right-hand thread! I forget which year they changed over... Also, you need to use a thin-walled socket.

 

[Rocky]

Careful, try removal as a left-handed thread first. Don't strip it out trying it as a right-hand thread! I forget which year they changed over... Also, you need to use a thin-walled socket.

Just to follow up on this advice, when I bought the T100S there was a bolt in the tach drive boss to fill the hole.
It was rusty and looked like a hardware store bolt so I ordered a correct bolt (blanking plug) and removed the rusty bolt.
Some nitwit had screwed a right-hand threaded bolt into the left-handed threads. When that rusty bolt came out it took most of the threads with it.
I inserted the correct plug and tightened it as much as I dared. It soon fell out on the road somewhere.
I ordered another one, and since the threads were all but gone, I knew that I would probably never be able to fit a tach drive.
I buttered the threads on the new plug with some liquid aluminum and screwed it in place to harden.
The plug has been in there since 1996 and has never moved.
Later on I bought an electronic tach from Mick Hemmings in England that runs off the ignition.
The T100S didn't come with a tach, but I like the look of a balanced instrument cluster and wanted that.
It's not an exact copy of a Smiths, but is close enough.
I thought I would toss this experience out just for the sake of interest.

 

[Jimmie]

Just to follow up on this advice, when I bought the T100S there was a bolt in the tach drive boss to fill the hole.
It was rusty and looked like a hardware store bolt so I ordered a correct bolt (blanking plug) and removed the rusty bolt.
Some nitwit had screwed a right-hand threaded bolt into the left-handed threads. When that rusty bolt came out it took most of the threads with it.
I inserted the correct plug and tightened it as much as I dared. It soon fell out on the road somewhere.
I ordered another one, and since the threads were all but gone, I knew that I would probably never be able to fit a tach drive.
I buttered the threads on the new plug with some liquid aluminum and screwed it in place to harden.
The plug has been in there since 1996 and has never moved.
Later on I bought an electronic tach from Mick Hemmings in England that runs off the ignition.
The T100S didn't come with a tach, but I like the look of a balanced instrument cluster and wanted that.
It's not an exact copy of a Smiths, but is close enough.
I thought I would toss this experience out just for the sake of interest.

View attachment 40412

Hi Rocky/GP: Good idea and I will look up tach you purchased. After reading my manual I decided it was WAY TOO COMPLICATED for me to attempt. Like you, I think two dials look nicer and I still like watching the tach. I found some caps that I am going to see if they thread on.

 

[Jimmie]

Hi Rocky, after checking out the many electronic tachs I decided it was more trouble than worth it to me in reading the instructions re calibrating,etc. I will cover hole with a metal cap or a sparkplug cap that fits tight, using a little glue. I don't ever run her to redline anyway maybe 4,000 rpms momentarily. I mostly ride on back roads at 35-40 and 50 on the highway at certain times when the road is not so busy. I will send you a picture of my adaptation.Jimmie

 

[Rocky]

COOL