BSA - Gold Star - Clutch Notes

Here are some notes on a clutch job on the Goldie.
The original six spring BSA clutch was a real dog. It slipped and required frequent adjusting. Most Goldie owners quickly changed to a four spring pre-unit Triumph clutch. Better options exist nowadays; including a Suzuki conversion or a belt drive. The Triumph clutch is much less expensive and readily available.

Nice new Triumph chainwheel (clutch basket as some call it) ready for fresh plates. On the early 4 spring models, notice that there is a shoulder on the clutch center hub which prevents the last friction plate from touching the chainwheel. Later models allowed for this, making the clutch much more stable and have less wobble. On these clutches, insert a plain plate first. It will float without touching the back of the clutch basket.

As with any clutch job, double check alignment between chainwheel and engine sprocket. Use a machinist's ruler; not your kid's plastic one. And, Yes, I have not tightened the springs down all the way in the photo.

If there is miss-alignment, look for spacers and shims behind the cush drive (schock-absorber unit). Notice that there are two spacers on the crank shaft. The new chainwheel did not need the smaller one for alignment. A .064" shim however replaced it for perfect alignment.


BSA had the The Good - The Bad - and The Ugly in the Gold Star. The good was the engine...fantastic, hand assembled  matching parts for a 7000 rpm big fin race motor. The bad was the lousy clutch. The ugly was the cush drive nut. It required a spanner to remove, and a whack of the hammer to tighten it. The official shop manuals even show the use of a drift and a ball-peen hammer. This would concern me given the length of the crank shaft, and the potential of bending it....even the slightest amount. You can see that the old nut has seen its days of hammering. SRM engineering sells a nice hexed nut that can be torqued down to a specific number (65 ft-lb) to assure a tight fit. By the way, notice that I wired the inner primary case retaining bolts so they don't vibrate loose.  The rest of the assembly is standard; tension the drive chain properly by adjusting the transmission bolts. Notice that this is a single-row chain; something that was common in post-war machines of the 50s.

When doing maintenance or a routine inspection of the primary drive system, alway take the time to check transmission mainshaft runout and offset. Also check the clutch sleeve and its bearing surfaces for elliptical wear. Photo above shows a Triumph clutch sleeve adapted to a Gold Star shaft being checked. It turned out that out of three used units, only one was within reasonable specs. The roller bearings that the chainwheel rides on bear against the surface that the dial indicator is set against, but also on the race that is just below the point of the indicator. Both need to be checked for uneven wear to minimize inherent wobble.

From Armand's Motorcycle Pages

If you require adapter for conversion from BSA 6 to Triumph 4 Spring Clutch please contact me. Approx Price 70.00 Euro