C15, engine dating, threads and frame repair question

[shoal48]

Good day all, I rebuilt and ran a C15 in the 60's as a 16 year old then went on to cars and other bikes but recently became the proud owner of a C15 which was completely stripped 35 years ago and has been just boxes full of bits since then.
I am sure I will have many questions to ask the experts on this forum over the next few months but I have a couple of questions and an issue I would value an opinion on.

The first question really is looking for confirmation & relates to the age of the engine, the bike was first registered Sept 1961 so I would have expected the engine to be 1960 or 61, which I believe would have had number in range starting 11001 for 1960 or 21251- for 1961 but The engine number is C15 42**

I believe the first year of production, 1959, started numbering at 101 but I had read they only produced a couple of thousand so I was a little puzzled, but on reading Mr Ratio's book on singles he indicated that they produced about 10,000 in the first year. Based on this,  I believe my engine was probably made midway through the 1959 production year. Can anyone confirm that this makes sense?.

The second, actual question was about threads. I have found several different references to the thread size for the gearbox side outer cover screws but unfortunately I have found conflicting information & just need to get the right helicoils to repair stripped threads. The threads are either 1/4" BSW or 1/4"BSC, both 26tpi but different angles on the threads. Ebay sellers will supply kits of cap screws for this casing in both threads so I am wondering whether BSA used a fine thread early on then moved to BSC later, which I one reason I was trying to date the engine.

the last thing, for now is looking for advice. I know this topic has been covered before, but again, I have seen differing advice. The frame tubes that support the side stand and rear footpegs have been bent down, the sidestand side about 3cm, at the sidestand lug. The other side bent down about 2cm, midway along the tube.
One bit of advice was to try and straighten the tubes cold with a length of scaffold pole and the more common advice seems to be get frame in a vice and heat tubes before trying to bend them which would be my inclination but I guess the frame is brazed together so is that why some suggest cold straightening I only have a MAP gas torch so not sure whether this would provide enough heat...does it need Oxy acetelene    Has anyone got experience of this. Sorry if this jumble of questions causes confusion, I will try and be more precise as the big jigsaw progresses.

[shoal48]

I successfully managed to straighten the bent frame tubes today, put frame in the workmate, wet rags on the next joint down and heated with a MAPP gas soldering torch, the tubes are fairly thin & it took a few minutes to get enough heat in them to soften the metal so I could straighten them with a bit of scaffold tube so all good.

now I just need to understand whether BSA used 1/4" BSF or BSC screws in the engine casings in 1959/60.

[Rupert]

All the 1/4" casing screws on your engine (and used up to the end of the 1968 season) are 26tpi. Both BSF and BSCy are 26tpi at 1/4" so they are in effect interchangeable in terms of the casing screws. The only ones you will now find easily available are BSF which are perfectly OK.

[shoal48]

Thanks Rupert, much appreciated, I have some 1/4" BSF vcoils so now I can go ahead and sort out the casings.

[JABBA99]

Engine C15 4200 was despatched in February 1959.  1960 engines started at C15 11001.  Hope that helps.