Tech Tip: Fixing Loose Clutch Hub Screws

Have you ever read about the those 6 small screws that retain your clutch hub center (and rubbers) working loose inside your primary?

Some of you may have, and chances are some of you haven't...

Today I wanted to cover an original BSA Service Bulletin dated from the 1960's that offers some basic info on how to retain those pesky little screws from working loose 

I will also cover some tips on what I like to do here at the shop that is not shown in the BSA Service Bulletin

The info we are covering is for both 3-spring clutches and most 4-spring clutches on both Triumph & BSA applications 

Lets dive in..

Clutch hub assembly 

There where a few types of clutch assembly's fitted to both Triumph & BSA models (unit and pre-unit) with the popular 3-spring and early style 4-spring clutch

Although slightly different, they are very similar in the parts they use, design and functionality 

The clutch hub assembly is located inside your primary cover and mounted on the mainshaft by a taper fit 

Internally the hub consists of shock rubbers, a spider, retaining plates, 6 screws (some use bolts) and a center sleeve 

To retain all the internal hub parts listed above, the outside screws must be tight and secure to allow a properly functioning clutch 

If all is done properly, you should have a reliable and secure clutch hub assembly 

The problem 

Now that you understand the basic role of the clutch hub assembly, lets cover the real problem 

The screws that retain the front and back plates are typically a counter-sunk style single slot screw that is threaded into the center housing of the hub

Without properly tightening down the screws they could work loose 

When this situation happens, you could be left with an undesirable clutch action 

Not to mention that you should not have any loose screws "floating" inside your clutch and primary area as that could be catastrophic 

BSA Service Bulletin (The solution) 

Click on the image to above to enlarge (you can also print, share, and save)

The BSA Service Bulletin shown above was sent out to both west & east coast dealers that showcase the loose screws problem while offering a simple solution 

According to the bulletin, BSA suggested that each dealer (or mechanic) use a small dab of Loctite to retain each screw while ensuring that each of the 6 screws are tight, evenly 

For those questioning "which Loctite should I use?"  - blue Loctite should be employed as your first choice of thread locking sealant as red sealant may be too difficult to remove upon future disassembly 

Modification & tips

While I do agree that Loctite does in fact work, I like to go the extra mile to ensure that each screw is tight and will not back out 

The modification I like to do on all of my clutch hubs for both road use and racing consists of drilling a counterbore and peening over the countersunk screw to prevent it from backing out 

By adding a counterbore the screw head now has a "valley" which will allow the head to be deformed in the divot once peened over  

For this modification you will need a mill or drill press, drill center and a vice (or clamp) 

I take and mount each plate (front & back) on my milling table to make sure we have a rigid and stable set up

For this set-up, I’ll clamp my hub into my Kurt vise 

From there I insert my drill center and find the location I want to perform the counterbore which would be right on the edge of where the countersunk bore begins 

A few "pecks" and the hole is ready

When you are done, insert your screw and make sure it is tight

From there you can peen over the screw head and it should look like the photo above 

Now you can feel confident that the small screws are tight and secure 

Replacement parts 

Should you be in a position to rebuild your clutch hub or you are seeking basic replacement parts please checkout some of the following links in the chart below..

Thanks for reading 

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Ride safe!