New Replacement BSA A50 & BSA A65 Valve Springs 1962-1972
BSA A50 & BSA A65 Valve Springs
As we all know, vintage BSA parts can often be hard to find, especially new quality parts and BSA engine parts. For the BSA Unit Twins we have found that the "UK Made" valve springs to be a problem that could have a catastrophic effect on your engine. We highly recommend reading this blog before you make your next purchase on a new valve spring set for your classic BSA A50 and/or BSA A65 twin.
First off, the generic "UK made" valve springs do appear to be of quality. We happen to stock a range of "UK made" valve springs for both Triumph and BSA models. The springs that are a problem are specifically for the BSA twins from 1966-1972. So whats the deal? The outer valve spring has an extra coil, and the diameter of each coil is larger causing coil bind. Coil bind is when your valve spring interferes with another coil. Coil bind can happen to both inner and/or outer valve springs. The "UK made" valve springs in conjunction with the stock cam and profile still causes coil bind. Unless you machined the bottom valve spring cup the springs are useless. The valve seat pressure is also to weak, which would cause valve float.
"Premium" BSA valve springs are sold in a complete set of 4 inner valve springs and 4 outer valve springs.
The solution to this troublesome problem are the new BSA valve springs that we now stock for all A50 and all A65 unit twins. This spring set is made in Germany and is highly suitable for standard road use motorcycles. With this set not being made specifically for a BSA unit twin, hence the term "suitable", you may have to slightly file the bottom of the outer spring to fit the cup. A 5 minute job which can be done quickly without hurting the integrity of the springs. Below are the specifications on the new BSA valve spring set that we stock and highly recommend. You can settle with "UK made" BSA valve springs for 45 bucks or so and perhaps wipe your cam, motor, or you can go with a quality set that works. The choice is yours. See this link to purchase your BSA A50 & BSA A65 valve springs today.
"Premium" BSA valve springs are made in Germany and are excellent quality replacement springs for the "hard to find" original springs.
Seat pressure check using a Rimac valve spring tester. @75#
BSA 650 cylinder heads from 1962-1966 were somewhat different from the later variety. Using this spring set, you should have no problem interchanging them with both early and later heads. We highly recommend that you have your installed valve height as close to @1.300" as stated below. Slightly over and slightly below will not hurt the performance (+.020 / -.020). Shimming may be necessary. We do not recommend using this valve spring set with high lift cams. Valve spring set will work with the standard cam and "sports" cam under BSA part number 68-0103 and 68-0473. Installed valve height @1.300" is recommend for a "range" of BSA cylinder heads assuming your valve seats are in good condition.
Valve spring installed height: 1.300"
Valve seat pressure (closed): @ approx 75lbs
Collapsed length: .740"