Triumph & BSA 3-Spring Clutch Thrust Washers
BSA & Triumph Clutch Thrust Washers Explained
As time passes by over the years, there seems to be a bit of confusion on the Triumph & BSA twins 3-spring clutch thrust washers. In fact, there are two types of thrust washers and two types of clutch hub sleeves that where fitted to many Unit Triumph & BSA twins. Below I would like to show you in detail of how to identify what parts you currently have, and also what parts you need.
Shown is the "early" version and "late" version of the clutch thrust washer as fitted to Triumph & BSA twins, also singles.
First off, there are two types of clutch thrust washers. We often refer to them as the "late" and the "early" variety. The later Triumph clutch thrust washer has one part number as also shared with the BSA models under 57-3931. The early thrust washer has two part numbers, one Triumph, and one BSA, both are the same part. The Triumph clutch thrust washer part number is 57-1735 (T1735) and the BSA part number is 68-3278. The Triumph & BSA early clutch thrust washers where fitted to twin cylinder models including the 350, 500, and 650 twins with the 3-spring hub only up to approx 1969. According to factory parts books, the "late" clutch thrust washer was fitted to Triumph & BSA twins from 1970 & on.
Left sleeve is the "early" type and the right sleeve is the "late" type. Notice the inner grooves are different? That is what dictates what thrust washer you need.
You are probably wondering... what is the difference? The difference is that both "early" and "late" thrust washers have a different I.D. (internal diameter). The clutch hub sleeves themselves where machined differently to accept the different thrust washers. As shown in the photo above, the left hand side sleeve has a smaller O.D. machined "step", that is to accept the early 57-1735 / 68-3278 thrust washer. The right hand side sleeve is the "late" version. You can clearly see that both look the same but the "late" sleeve has a wider machined O.D. Look at both red arrows to visually see the difference. You must use each thrust washer with the correct sleeve in order for them to work and fit properly together.
If you are performing an overhaul on your clutch, and you not sure which thrust washer you need or not sure which sleeve you have, use the specs below and compare with your hub. I have seen many cases where an early sleeve has been fitted to a late model and vice-versa. Sleeves are interchangeable for all 3-spring clutches, but you must use the correct thrust washer in conjunction.
Thrust Washer Types I.D. (approx) O.D. (approx)
Early Clutch Thrust Washer (57-1735 / 68-3278) 1.836" 2.608"
Late Clutch Thrust Washer (57-3931) 2.020" 2.608"
Original Triumph clutch thrust washer. Notice that one tab is missing / broken?
The original clutch thrust washers where made from two types of materials into one piece. The back half was a steel type material and the front half was made of bronze. The problem with the "early" original types, as shown above, the factory used metal tabs to secure the thrust washer from rotating. The metal tabs would eventually break off and get crushed by your clutch chainwheel. Original thrust washers never had a precise fit, they where also marginal.