Tech Tip: Indexing The Clutch Operating Rack On BSA / Triumph Unit Singles (Excluding Cub)

Tech Tip: Indexing The Clutch Operating Rack On BSA / Triumph Unit Singles (Excluding Cub)

When you are finished servicing or overhauling a Triumph or BSA unit single gearbox there is a very important step that must be set-up correctly before you you offer the outer gearbox cover to the inner gearbox cover.

If you haven't already figured it out today we will be talking about how to properly index your clutch operating rack on both Triumph and BSA unit single models.

If the clutch operating rack is not indexed properly you will not get the correct pull and your rack could bind with the end of the mainshaft.

How Do I Know?

I have first hand experince when it comes down to this procedure. I resurrected and restored 2 BSA unit singles, a 1965 C15 (SS80) and a 1965 B40 Enduro Star.

The first time I experienced this error was when I was putting my C15 together.

I sealed the outer cover using threebond 1184 and offered it to my case. All worked perfectly. A few days later I noticed a small amount oil coming from my outer cover.

What a pity...

Most folks that know me will tell you that I cannot stand oil leaks! I don't mind a small amount of residue but leaks I cannot tolerate.

Upon removing the cover, cleaning, prepping then adding more sealant I then installed the inner cover back onto the case. I added oil and there where no leaks!

Upon starting the bike I pulled the clutch lever in to "free the plates" and noticed the "pull" on the clutch lever would stop half way before touching my grip?

After thinking it over i came to the conclusion that I forgot to properly index the clutch operating rack.

I learned the hard way

Below I will show you all how to properly index your clutch operating rack the correct way; the first time, so you don't have to make the same silly mistake I did.

Indexing your clutch operating rack takes less than 1 minute. Failing to do so can cause hours of additional work.


Indexing the clutch operating rack

Not all Triumph and BSA unit singles came with a clutch operating rack. Most models from 1965 and on also known as the "side points" models feature this new addition.

Models with Lucas "distributors" will not feature the clutch operating rack so this tech post would be irrelevant to you... but you can keep reading if you would like.


 Compatible Models Year
BSA C15 / B40 / B44 / B40 / Etc 1965-1973
Triumph TR25W / T25SS / Etc 1968-1972

Rupert Ratio

Most BSA and Triumph unit single owners have a book by Rupert Ratio called "The Ruper Ratio Unit Single Manual". This book (volume #1 - The Engine) touches base on this subject very briefly (1 short paragraph) on page 123 at the lower half of the page


Ruper Ratio "The Engine" - Page 123

Clutch operating rack adjustment (Rupert Ratio) - click image to enlarge

I will make indexing the clutch rack very easy with 3 simple steps that the average back yard mechanic or caveman can do it.


Parts & there names


Identifying each part and knowing the respected names will better assist you along the way when indexing you’re clutch.


Outer Cover Parts Identification


Step #1

With your outer timing / gearbox cover and clutch rack in hand ready for assembly you want to first make sure that the clutch actuating arm (where the cable goes in) is at a position of 1 o'clock.


Step #1


*Notice the positing of the cover in reference to 1 o'clock - make sure your cover is positioned in the same location to avoid confusion.

Step #2



Once you have the clutch actuating lever at 1 o'clock you can now offer the clutch rack into the pinion gear.

When installing the rack the rack must bottom out against the back side of the case. Doing so will mean that the clutch actuating lever will have to move out of position.

Regardless of the clutch actuator position once installing the rack, the rack must be fully bottomed out and the clutch actuator must be at the 1 o'clock position,

*It will take a couple minutes installing and removing the rack into the pinion gear.

Step #3



Once the rack is installed and the clutch actuator is at the proper 1 o'clock position you can then seal the case and finish up the job.. don't forget the ball bearing that goes in the rack too! 


I have also made a short clip showing you how to properly index your clutch rack. Click on the video above to watch the YouTube video.

Click here to view the Classic British Spares YouTube channel


Thanks for reading

Well there you have it! I hope this techs post serves you well.

Should you have any questions please let us know by commenting in the section below!

Thanks for reading and watching today.


  • tim

    thanks very much for the info on the clutch rack. i had not been able to source clear instruction from the workshop manual on this particular part of assembly.

  • Mark

    Thanks I been struggling for a while. Well happy

  • Lars Holm Christensen

    Shit, you made my day, thanks👍👍

  • ed smith

    great job on the tech stuff ! like all the pics that goes with it

  • Classic British Spares

    @Dave – Thanks for reading! I knew I wasn’t the only person that experienced this! Cheers :)

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