Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board The A70 Lightning story (rebuild)

You could be right, I think by July it was coming towards the summer shut down so May might be more realistic as they were already paying dealers a a good wedge of money to repaint them. My “thunderbolt” (which is really a Lightning dressed up as a thunderbolt) is EE, that was painted black… but the paint underneath is was dove grey, as was seen with all the contact points were exposed (like swing arm removed etc), the thunderbolt frame I have is DE and that is the same.

My friend just sent me this… but it’s a good example of the original paintwork, you can still see the halo from where the original stripe was
EBay Lightning

My bike came off the line the same year and month, its also GE, the frame was black, AFAIK, the change from Dove Grey to Black started in May 71.

FWIW my 1971 A75RV certainly was dove grey overpainted (badly) with black.
I could hear the dealer in US saying to the most junior fitter "Heres a tin pf black paint----paint all the grey on that BSA so that we stand a chance of selling it"!
The bike is matching numbers PE (November 1970).

Thanks for everyone that chimed in on the paint selection. I am not sure any of the participants have a copy of the 1972 parts correction put out by BSA in Maryland. It give the colors for the 1972 model and correct all of the part numbers for the USA bikes. You will see that Etruscan Bronze is only mentioned for the A65T model. The A65L is shown as solid Firebird Red and the A70L chrome Firebird Red with white lining. I believe that is the scheme of the Donaldson bike. The bulletin will not load in a format accepted by the forum. If you would like to see it send me your email with the private message feature. Lloyd L

Hi Lloyd.

As its a fine day in the UK today, I grabbed the side panel I bought from the garage and took it into the sunlight to take a photo of it, as you can see the lacquer is poor but I was amazed by the change in the colour especially from something with poor lacquer.

I have attached the photo from ebay as when I bought it, in poor lighting it looked not far different from that, but in the sun it really shines. At some point I will get this panel colourmatched properly, Im still trying to get my workshop setup but will be getting some proper spraying equipment, which will get me away from the base coat and 2k lacquer aerosols.

When I purchased the bike the PO gave the cart he made to do the engine, thanks Ron. Before I got started I decided it was time to give it a redo. I am attaching the before and after pics. All that is left is to get started with the engine rebuild. Lloyd L

Thanks to the link given on the other A70 thread, I have found the image of the UK styles (4 gallon tank) I was referring to


BritBike link

Gee, Allan. That thread is a blast from the past.
One of the posts on the thread has a link to the Triples Online A70 thread. That TOL thread is a real gold mine.

Today I removed the engine from the frame and cracked it open. Next I will be cleaning all the parts and checking the threads. I will also be checking all of the critical dimensions.

I just found that the sludge tube and plug are missing. Does anyone have a spare or know of a source to purchase?

That's a bummer. Those are some of the special unobtainium A70 parts.

I need to read that. I whip through the attached thread and found the A70 image I referenced earlier (which I was kinda pleased about as I did have it on my phone… but like a lot of images, the phone fairies must not have transferred them to the new one lol)





Aren’t they (isn’t it rather) smaller like the A10 plugs on an A70?

Lloyd, would it be possible to share the casting number off the back of the cylinder head (between the splayed ports?) there was two different twin carb heads for oif, different part numbers though I “think” only one is ever refrenced. One of the differences being, 5/16 UNC threads for the outer rocker box studs on one and 5/16 UNF helicoiled bolts (or studs may have been original) on the other, the casting around the pushrod tunnel was different.

On the two I have the port size was slightly bigger on the higher numbered one (30mm if I remember rightly) and 29mm on the other (with the UNC threads)

Allan, The casting number is 71-2202 There are no helicoils in the rocker bolt holes.

Another question, what is the thread size for the sludge trap plug?

5/8" UNF (19 tipi)

Would you check again, 5/8 UNF is 18 tpi. Thanks Lloyd L

The 19 must have been a typo. It's definitely UNF. Grab a bolt next time you're at the hardware store to check.

Are you sure about that? I thought it was 5/8 20 UNS

I am positive, the designation UNS stands for Unified National Special, which is rarely used.


Buying a bolt tomorrow!

Beezer used some strange threads over the years.

Unified special (or unified constant) was one of them.

BSA did use quite a few 20 tpi threads, but I think they were 20 tpi Cycle.

Morgo has a good range of hex socket crankshaft plugs Morgo Plugs
It could well be a BSF thread as BSA?Triumph were smoking some weird stuff back then, from memory the new for 73 disc fork legs were tapped 3/8 BSF and fitted with a stud with 3/8" UNF on the opposite end for calliper locknut.

Morgo's HB11 looks like a possibility, might be worth asking them what one fits an A70?

These look identical to the ones SRM are selling and use the same ID numbers on the plugs... I think if they didn't taper the plug at each end they wouldn't sit so deep in the crank web.

The HB11 is much shorter than the ones they list for the A10/A65 cranks (6.5mm compared to 11.5mm).

When they dropped the cycle thread they had a habit on the 20 TPI Cycle to replace them with a UN special where the thread is UN thread angle etc using 20 TPI. They do not interchange well.

Interestingly though, BSC thread has a 60-degree thread angle the same as UN threads, and NOT a 55-degree thread as people wrongly assume it to have the same thread angle as BSW & BSF.