< AllMoto's Motorcycle Investor mag


allmoto logo

Motorcycle Investor mag

Subscribe to our free email news

Sunbeam S7

Our bikes - Winston the 1947 Sunbeam S7

(October 2019)

by Guy 'Guido' Allen, pics by Lou Martin, Ben Galli Photography and author


Rebuilding Winston the Sunbeam S7

After some incredible highs and lows we might soon have a runner.

Sunbeam S7

The story so far

Some years ago I bought a 1947 Sunbeam S7, the first version, which in its heyday was a novelty and promoted as a 'gentleman's tourer'. It was described as being an example of the brave new world of post-WWII transport.

The tandem twin 500 engine was unsuual at the time for being largely of aluminium construction, with an overhead cam. It ran shaft drive and heavily stylised looks that fitted in very well with late 1940s vehicle visuals.

Initially penned by Earling Poppe for BSA, one of its calling cards was distinctive balloon tyres that matched those on a heavyweight Harley-Davidson of the period. It had a traumatic entry into the market thanks to some issues with vibration and reliabilty, and was effectively re-engineered for the next model, the S7 Deluxe.

The easy visual differences are the first model were black livery with reverse handlevers (pivoted from the end of the handlebars), while the second was green with conventional levers.

Our example was running beautifully the day it spat a conrod through the cases, though it kept running as a 250 single, albeit pumping out a cloud of oil!

We immediatley ordered a period replacement crankcase from (of all places) Florida,via Ebay, and that was stolen out of the back of a pick-up when the seller decided to go fishing. Heaven only knows what the addled nitwit who stole it though he or she was getting!

WIth yet another replacement crankcase sourced locally in Australia, we tried again. And this is where we pick up the story...

Sunbeam S7

The build

You know you’re in trouble when you walk into a workshop you’ve never before clapped eyes on and are greeted with. “Ah, you’re here to see Winston.” This line is delivered in tones you might expect from an undertaker. Indeed, I am in to see Winston, or at least bits of him.

You see Winston is my 1947 Sunbeam S7. This is the famous (infamous?) ‘early one’. The version with all the problems, the one experts advise you must have deep pockets to own. Yep, that one. There’s estimated to be less than 200 left in the world and I strongly suspect you’d be lucky to find half of them actually running. Mine isn’t among them. Well, not at the moment.

Doug Fraser Sunbeam S7

Okay, I’m in the workshop of Doug Fraser (above) who builds industrial electrical switchboxes for a living. And no, I haven’t started collecting switches. In fact, Doug is widely recognised as one of those shed-dwelling geniuses (he’ll be terribly embarrassed to read that) who could probably run NASA with a hand drill, a shifting spanner and screwdriver.

A BSA nut renowned for the home-built V-twin he completed some years ago and whose most recent project was a very tasty electric-start trail bike built out of a B50, he also does the odd rebuild and machining job for fellow motorcycle tragics. In this case, he was sent my engine by a mate – Phillip White – who recently took over Winston’s rebuild.

Why are we doing this? Glad you asked. It’s part of the ongoing war I’m having with the wonderful All British Rally, which in the last few years has tentatively cost me at least 10 grand. First Winston tossed a leg out of bed (a colloquialism for breaking a conrod and spitting it out into the nearest paddock), then I hit a roo on my T160 Triumph. The great hopping hairy idiot is now deceased, but the T160 survived and has been repaired at great expense to management.

                Newbold Sunbeam S7

Back to Winston. I kind of got part way through the rebuild, with the aid of old mate and fellow Yamaha SR500 club member Paul Newbold (above), when we ground to a halt. The engine is – there’s no polite way of saying this – a prick of a thing to assemble and I just ran out of time and talent. What tipped me over the edge was a call from young Mr White (a former aircraft engineeer and, like me, an Iron Indian Riders member, pictured below), to come and ride his freshly-assembled Sunbeam S7 Deluxe. That’s the model after mine, with many of the issues fixed, and he’d cobbled it together out of a trailer-load of bits.

Phillip White Sunbeam S7

When I say cobbled, it’s a damn nice machine and a quick run on it revived the good memories I had of Winston. “It’s one of the toughest bikes I’ve ever had to put together,” quoth White, which went some way to making me feel better. So I promptly flick-passed Winston to him.

Along the way he has decided the powerplant needed further surgery, though I’d already fitted new rods and pistons. Doug’s diagnosis includes the tops of the pistons need valve cutaways – he reckons we might get away without it, but S7s have been known to tap the valves and it’s better to play it safe.

He’s isn’t too happy about the head cap, either, which he reckons has some hairline cracks that need fixing. Plus, he’s clearly offended by the broken fins on the barrels and plans to sort that lot out. Oh, and he reckons the rocker gear needs some shimming to get it sitting right. Come to think of it, there’s a bit of float in the oil pump shaft, so that will have to be sorted. You can see how these projects quickly balloon into a major exercise.

Sunbeam S7

Despite all those dramas, Doug had some kind words for the powerplant: “It’s actually a pretty good design,” he said. Interesting, as it was also advanced for its day. Overhead cam alloy engines were few and far between way back in the 1940s.

He also added it could easily be taken out from 500cc to 750. Of course I instantly said let’s do it. No dice, was the response. Sadly the bronze worm shaft final drive just wouldn’t cope with the extra power. He’s right, as the factory built a ‘sport’ version of this machine, which quickly chewed out drivelines. Bugger. Then again, any extra urge would only overwhelm the already pathetic brakes.

Once the machining is done, Mr White will hopefully turn his attention to the assembly. He’s threatened to perform a few upgrades along the way, such as replacing the original six-volt generator with a 12-volt conversion based on a unit out of a Kubota industrial engine. We’ll see about the latter, as I’m not keen about changing the looks of the original, which has done very little work since the last rebuild.

And that’s the quandary with projects like this. The means is readily available to make these things more reliable, but how far are you prepared to change the original motorcycle? Cost comes into it, as does the potential to devalue the machine in a market that places a premium on originality.

Another factor to keep in mind is how the bike is likely to be used. I’m never going to tour on it, and certainly not at night, so the luxury of the good lighting that a 12-volt system enables is far from necessary.

I reckon we’re still months away from having a running motorcycle, but it will be worth the effort. I’ve never really had any faith in the thing hanging together, so maybe at the end of all of this I can head out for a joyride with some degree of confidence in making it back under its own power. That really would be a novelty…

See part 2 - the completed machine

Sunbeam S7

Sunbeam S7

Know your S7s
The S7 was a brave post-war design intended to be ‘gentleman’s tourer’. Three generations were built:
S7 in black with reverse hand-levers;
S7 Deluxe in green with conventional levers and significantly re-engineered engine;
S8 in a few colours, with slimmer conventional wheels.
Production went from 1946 through to 1956.
There is an active Australian club (dawsonadrian@aapt.net.au) and a ready source of spares and knowledge in the UK from Stewart Engineering (stewartengineering.co.uk).

(Pic above is from a 1948 road test in Motorcycling magazine, UK.)

See the Our Bikes page for more


Produced by AllMoto abn 61 400 694 722
Privacy: we do not collect cookies or any other data.

allmoto logo


Try our books...

Travels with Guido


Facebook feed


YouTube feed

Email newsletter


News archive


Our Bikes stories

Travels with Guido columns


About AllMoto

Email me