Why The 1970 BSA A65 Is The Best Year

Why The 1970 BSA A65 Is The Best Year

1970 BSA A65 Lightning

There are still many opinions today of which BSA A65 that was produced is deemed to be the "best" year. It appears today that everyone automatically believes that they have the best year A65 simply because they own it.

Today's post Is an explanation of why I personally think and feel (with proof) that the 1970 BSA A65 was the "best" model year produced - hands down. If you are looking to purchase a BSA A65 or simply want to learn more information then I suggest that you give this blog a thorough read. Alright - let's get to it.

Brief History

BSA A65 Engine Drawing

Artwork of a BSA A65 unit twin engine - pulled from a period magazine article


In 1962 the Birmingham Small Arms company (BSA) launched a completely new designed motorcycle based off of the BSA A10 platform. This new model was called the BSA A65.
1962 was BSAs first attempt of making a unit construction twin. Gearbox, primary and crankshaft was now housed into a single case or "unit". Very similar in design to the BSA C15 and B40.
The "A" in A65 was to represent the group that the A65 belonged to. The "65" was short for 650 which represented the capacity of the motor - 650cc.
The BSA A65 model range was launched one year before Triumph released there first unit construction twin in 1963. This gave BSA a head start as Triumph was their biggest competitor.



BSA A65 Frame Design

 BSA A65 "dry frame" blue print

Probably one of the best features for the 1970 was the "dry" frame. Just the next year in 1971 (also carried on in 1972) BSA designed and produced a new frame in which the oil was located in the center frame down-tube. Also known as the "oil in frame".


The oil in frame design ultimately put the nail in the coffin for the BSA motorcycle company and severely hurt Triumph during the fallout. BSA had control, influence, and power over Triumph at that time as BSA owned Triumph. Many are not aware that the Triumph oil in frame was designed by BSA.


There are many opinions on the oil in frame models. From a value point of view prices typically drop for BSA and Triumph models from 1971 and on due to the oil in frame design. Although the oil frame models handle very well they are not appealing and they also have there flaws.



 1970 BSA A65 Clear Hooter Horns

1970 BSA Lightning with dual Clear Hooter horns and the Lucas 6RA relay on the head stay


Just like the 1970 Triumph Bonneville the BSA lightning was the only model for 1970 that featured dual horns. For those that are familiar with the dual horns they are called Clear Hooter horns which today are extremely difficult and hard to locate.


Although the 1970 BSA Lightning featured dual horns not all came equipped with them from the factory. Many where fitted with 1 single horn or dual "thunderbolt" horns which where different in style, shape, and sound.

Lightnings that came equipped with dual horns had a special head stay bracket in which one could fasten the Lucas 6RA horn relay for the dual horns.


Base Studs

 3/8" BSA Base Studs

3/8" diameter base studs along with 3/8" size 12-point base nuts


The cylinder base studs in 1970 where changed from the smaller 5/16" diameter to the larger 3/8" diameter. It only took BSA 7 years to make this change - should of been implemented sooner.

The larger diameter base studs allowed a higher torque rating on the cylinder barrel. I heard of one instance in which a cylinder barrel lifted from the crankcase on an early model that had 5/16" studs... according to John Healy.


The 3/8" base nuts where also changed from standard hex to the new 12 point nuts to allow easier adjusting when using a box end wrench.


Cylinder Barrel

Late Cylinder Barrel Cut-Out

Cylinder barrel fin cutouts as seen on this 1970 BSA A65 


Never seen before until the 1970 - A65 models where now fitted with cylinder barrels that featured cutouts above the cylinder base nuts. This change was also carried through 1972.


This new change allowed easier access for a box end wrench to slip over the base nuts. Previous years did not feature this design which made it more challenging to slip a wrench between the base of the barrel and over the nut.


Late barrels from 1970-1972 are getting harder to find today as they where only used for 3 years. They are not interchangeable with early models as they are suited (and offset) for the 3/8" diameter base studs. 


Stud Pattern

 BSA A65 Base Gaskets offset

 Bottom base gasket correct for 1970-1972 models - top base gasket correct for 1962-1969 models. Notice the slight offset on the stud pattern?


We now know that in 1970 BSA A65s now had the larger 3/8" base studs. Although the design is similar to that of the 5/16" studs, cases with 3/8" studs have an offset pattern.

It is still unclear to me why BSA change the stud pattern for 1970 models (also carried on until 1972). I can only assume that the reason why BSA changed the stud pattern was to accommodate the larger 3/8" base studs.



 Clutch Set-Up

 New clutch set-up on the 1970 BSA A65 - very similar to Triumph twins


Probably one of the smartest changes for the 1970 A65 models was the addition of a newly designed clutch actuator on the inner timing cover. This new change was influenced by Triumph. If you where to take one apart or compare a BSA parts to a Triumph you would see that the clutch actuator parts look very similar

The new clutch actuator allows a much smoother feel on the clutch lever for a more positive clutch release.

Notice that the outer timing cover has been changed as well. Inspection plug and an extra fastening screw - new for 1970.



1970 BSA A65 Lucas 40MM Coils

Smaller Lucas 40MM diameter coils and bracket - new for 1970


Normally 48MM Lucas coils where fitted to A65 models - 1970 A65's where fitted with smaller 40MM coils as usually found on most Triumph and Norton models. I am not exactly sure why this change was implemented. I can only assume that perhaps the large Lucas coils where not available or where to expensive.


The coil bracket to house the smaller Lucas coils where also changed making them a "one year only" part. 40MM coils and brackets are listed in the 1970 BSA 650 parts book only. 


Mirror Holes

Clutch Brake Mirror Holes

Mirror holes on both the clutch and brake perch - new for 1970

 Mirror holes on both the clutch and brake lever perch was a new design for 1970 models. Most laws in the USA (depending on the state) require to have at least (1) mirror on either the clutch or brake side. Mirror holes shown above accept an 8mm threaded mirror.

Earlier BSA models prior to 1970 did not feature this clutch and brake lever perch design. To adapt a mirror you would have to use the "clamp-on" style mirrors.




If you're familiar with early BSA A65 models I'm sure that you can come to the conclusion and agree with me that the 1970 BSA A65 is the best year based off of this information and experience.


From a buying, selling, and an investment point of view I personally feel that all 1970 BSA A65 models are the best choice. 1970 models retain there value better than any other year (except rare models) especially the 1970 BSA Lightning.


So there you have it - my 2 cents on why the 1970 BSA A65 is the best choice. If there is any information that I missed or did not touch on, please let me know by commenting below. I would appracite everyone to chime in using the section below. As always, thank you for reading today's blog post.


  • stev3po

    Here’s one for sale on Bring A Trailer.


  • Classic British Spares

    @David – not true… the timing side always had a bushing. If set-up properly it will last you a long time (change your oil frequently)

  • David

    I think after ‘67 they changed over to needle bearings on the timing side. Low oil pressure and crank end play. Can be remachined for better bearings. If not at 15,000 mi your riding a grenade.

  • Nick

    Well thought out article. However, I am currently looking at two A65s, both of which purport to be entirely original with matching numbers. One is 1967 and has the clutch actuator and the barrel cutaways listed here but not the coils. The other is 1970, has the actuator but not the cutaways. I haven’t actually seen them yet, only photographs but something appears to be amiss!

  • Gary

    I used to own a 1970 lightning. Looking for another one. Can you please give me some details.

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