what is the best length of shocks for a Thunderbolt?
mine are original oif but the chrome struts have gone and they seem low to me at 12" eye to eye. The BSA catalogues show a Thunderbolt oif with longer shocks than a lightning. can someone enlighten me before i open the musky wallet.
Parts book shows the same shock for both Thunderbolt and Lightning, Girling 64052497. I think they are 12.9" eye to eye. The old dry frame were longer than 12". Short shocks make the steering angle shallower and heavier steering.
This is an original Girling fitment chart in pdf form.
https://www.iansoady.org.uk/pdf_documents/GirlingMotorcycleSuspension.pdf
thanks for information.
my original white girlings measure 12.4"which is matched on the chart for 1972 specification. however it is the 1973 bsa catalogue which throws me as the thunderbolt is shown with higher rear suspension than the lightning and i m wondering why BSA changed specification at that particular time. an improvement or more rear wheel clearance needed?
Hi,
Is the tyre size different - 4.00 as opposed to 3.50?
Dave.
The 1971 OIF model range got widely criticised for the very high seat hight. Some time around 72, 73 they changed the hight of the frame seat rail and dropped the seat hight by around 1". You'll need to look closely as pictures (or bikes) to see if this lowered the top shock mounts or not. My A65 was a 71 model with the very high seat but after a crash in 72 the frame was replaced and the new frame had a lower seat hight. The ordinal frame was white and the replacement black. I have a feeling all the frames with the lower seat were black. I would not trust any BSA literature from 71 on. They were in real trouble and a lot of bikes were being built from what ever parts were about. This was the attitude across the industry, I had a Vauxhall car built at the time of a face lift. The brakes on one side were pre-facelift and other other post!!
hello,
mine is a black frame 1972 thunderbolt sold and registered in 1973.the catalogue photos i am referring to are on page 85 of roy bacons book, bsa twins and triples.longer shocks but what was the reasoning?
I may still have the catalogue somewhere. I really don't think the Thunderbolt and Lighting differed in the frame, shocks or set up. So far as I recall it was the tank (the Thunderbolts usually had the larger tank), the side covers and single carb. Frames and seats were identical.
You are right about those pictures in Bacons' book, very odd as there is visibly more clearance between the rear tyre and the mudguard on the Thunderbolt. Could this just be the pre-load setting?
You can't rely on colour catalogue pictures from this era as being precise. They were often manually "colour stripped" which meant highly skilled workers using knives and a light table to cut the pictures to remove the back ground and separate the colour groups for printing. This is all well before digital image processing, its all done by hand.