1953 BSA Plunger A7

[johncarter]

In 2021 with lockdown in full swing I needed a project and found a running but pretty tatty looking 1953 plunger A7 on ebay. All I had to go on were the ebay photos and a YouTube video of it running that the seller had posted. Seeing the video with the seller riding it around country lanes I thought, 'well it runs and sounds ok and the guy is happy to ride it, so how bad could it be?' It also had only one previous owner according to the registration document which seemed unusual, so I bought it. To be fair, the man who sold the machine to me did make it clear that it would suit, "a committed enthusiast with some mechanical skills and a well equipped workshop" or words to that effect. I interpreted that to mean it needed more than an oil change and new plugs which suited me fine. I can't claim misrepresentation.
I had it couriered to my home and then got a close look at it. I'd planned to completely rebuild it, using as much of the original as I could. However, on closer examination the cycle parts, which I had hoped would be reusable, turned out to be in, well let's just say, generally poor condition. The frame was straight, but rusty and pitted in parts but after blasting and a bit of fettling turned out well. The tinware was in very bad shape; completely rotten and only held together by paint and oily mud. The oil tank was good, the air filter and battery carrier was salvageable and the petrol tank, although badly dented and rusting was solid, so was reused. I didn't attempt to ride it prior to restoration because it was a death trap. The guy who made the YouTube video with the bike burbling around country lanes clearly differs from me in his assessment of risks. Brake linkages were flopping around, brake shoes were down to the rivets, cracked tyre sidewalls, plunger covers rusted through with different length springs, fork bushes badly worn with the wrong springs, notchy steering and a seized and incorrect damper assembly.
On dismantling the engine I found the bores were badly worn and were fitted with the maximum +60 thou pistons so new cylinder liners needed to be fitted. New standard sized pistons proved impossible to find at the time so I ended up having to buy +20 thou JP pistons and then bore out the new cylinder liners by +20 thou. Bit of a waste but needs must etc. The crankshaft had similar problems as the journals had already been ground, or maybe had just been worn down, over the minimum possible journal size. Not only that but the journals were actually tapered. I don't really understand how that is possible but hey, it happened. I managed to pick up a replacement crankshaft at Kempton Park autojumble complete with cases, camshaft and connecting rods. It was assembled so I had no idea whether the journals on the replacement were any better than the one I had, but I got lucky, and they were standard size and in good condition. I also managed to pick up a spare plunger gearbox at the same autojumble which turned out to be useful as well.
Despite meaning to do the engine rebuild myself, so much specialist engineering work was needed on the cylinders, crank and camshaft, it made it sensible to give it a proper engineer, so Rob at Bygone Bikes in Addlestone took it over and did a fantastic job. The Magneto and dynamo, when removed, both contained the wobbliest bearings I have ever seen. The dynamo didn't work and it was a miracle that the magneto did but both got sent off for an overhaul to Paul Lidford in Shaftesbury. Various bushes needed to be made due to the side stand, centre stand and rear brake lever lugs being vastly oversize and oval. Consequently, I bought an old lathe off ebay that usefully came with all of the paraphernalia needed for simple machining. With the help of a few You tube videos and some workshop engineering books I learnt to fabricate simple bushes and the like... Whilst an expensive way to get a few bushes made, there's a real satisfaction of making your own and I am building on these rudimentary skills...
The wiring was a mess with some sort of homespun tangle of wires, connectors, insulating tape and dirt but nothing that an injection of cash couldn't fix. A new loom from Draganfly, new headlamp, rear lamp, electronic voltage regulator and switch gear... i.e. a complete rewire, sorted it very effectively. I love the simplicity of magneto/dynamo equipped motorcycles and whilst I appreciate the limitations of 6 volts, being able to run on flat or no battery seems to me to be a good feature to have.
The wheels had loose and missing spokes and very poor rims so new wheels were built by Paul ? in Herne Bay... bit of a hike to drop off and pick them up but a very good job done. With tyres supplied by Watling in Redhill and brake hubs machined and shoes renewed I expected some decent 'of its time' stopping power. The rear is good but the front leading single shoe is a bit underwhelming. I'm hoping it will improve as the new shoes bed in.
As mentioned earlier the mudguards, headlamp and cowl and the fork and plunger covers were all past saving so had to be junked. With new steel mudguards from Feked I had to fabricate all of the brackets and fixings which took some time. The end result looks good I think, and has improved the power to weight ratio somewhat having dispensed with all the heavily valanced look of the originals. (Mind you, just cleaning the mud off it knocked kilos off the weight)
The painting I undertook myself. After my last effort at painting a motorcycle I swore I'd never do it again but I needed to keep the costs down and I wanted it finished by summer so I bought the paint in rattle cans from RS Paints and risked life and lungs.  The end result is, to my eyes at least, not bad at all. The purists might raise an eyebrow but I have a mechanically sound machine that starts and rides well and I love it.
This could be seen as a cautionary tale about buying motorcycles on ebay but despite the expense I don't regret the purchase for a minute. It's been a joy and education in addition to keeping me sane throughout lockdown.

[DAVE BRADY]

Hi John,

Good job and good write up.  There is nothing wrong with an 'individual' looking bike and yours look great.

Dave.

[idie]

From what you have said, I think you have made a lovely job of the bike. Another one back on the road.

[johncarter]

Thanks Dave and Idie... the only problem with finishing a project is what do next...

[DAVE BRADY]

Hi,

I suppose getting out and enjoying it is the next thing. If you are not already a member of the BSAOC then join up and get along to some events.  See if there is a Branch near you.

Dave.

[MGI]

Really nice looking machine...credit!