The sleeve valve motor is somewhat of a unicorn. It is a complex and unique beast that started out in early aircraft manufacture. The design uses a ported sleeve-valve that is meddled between the piston and its cylinder. The sleeve is caused to slide up and down inside the cylinder, and at the same time rotate about its axis. This oscillating motion allows the sleeve to open and close both the inlet and exhaust phases of the four-stroke cycle. Now you may understand what why we have chosen the word “complex” to open this article…!
The setup allowed the spark plug to be best positioned above the piston for maximum efficiency, however there were downsides such as a susceptibility to overheat, and they were known to burn oil at a rate of knots. In this article, John Ferguson provides a fascinating insight into his world of sleeve valve engines, and the motorcycles that contain these mechanical wonders.
— an article by John Ferguson —
Sleeve Valves, specifically the single sleeve valve engine for a motorcycle. Nope, I’d never heard of them either. As a young enthusiast with a couple of engine rebuilds to his name, I thought I knew a fair bit about engines until Wally Maynard gave a talk on “Ever Onward” at a Classic Motor Cycle Club of Victoria (Australia) meeting over forty five years ago. I was fascinated. Here was something completely and utterly different. A four stroke with ports like a two-stroke and no conventional valves. A lot of reading and research into “unconventional” engines followed.
No surprise then, that “Ever Onward” came into my care when the opportunity arose.
So what is “Ever Onward”? For a start, “Ever Onward” is not a brand, nor a marque nor slogan. “Ever Onward” is a statement of intent. The man who built it told me so.
The 1924 built 500cc Barr and Stroud single sleeve valve engine turned up near-new and still in the original crate in 1966. It could have become an ornament, but instead was built into a motorcycle as a vehicle for this interesting engine. You can rightly call it a “bitzer”, but I see it more as a re-creation of what was done in period. Until the late twenties, most motorcycle manufacture was a cottage industry where you bought a proprietary engine (Villiers, JAP, Blackburne etc) and a proprietary gearbox (Albion, Burman or Sturmey Archer), with some wheels from Enfield or British Hub Co, AMAC carb, Lucas, ML, or BTH magneto and a set of Chater-Lea frame lugs. Braze up a frame, make your own tank, put your own name on it but everything else is bought in. And so it is with “Ever Onward”. However, it was built to be ridden. Despite being all early 1920’s parts, it has 8” brakes front and rear.
With the bike came a sheaf of brochures and general information, but not much else. The VMCC (UK) didn’t have much more, so I thought I’d do something about that.
Barr and Stroud still exist, as a subsidiary of Pilkington Glass. They’ve always (since the 1890’s) been a precision optics company, making range finders, periscopes, binoculars and the like. With the armistice in 1918, business evaporated. So they had a crack at the proprietary engine market. A prototype engine was running in 1919, in New Imperial cycle parts, and was favourably reported in road tests at the time, but plainly was not a practical success because the production engines that emerged in late 1921 were a totally different design. The significance of the New Imperial connection emerges later.
The full archive of Barr and Stroud exists. It is enormous; the index alone is 188 pages, and the archive occupies 127 metres of shelf space. Sadly for me, there is no separate record of engine production available. After days of trawling through the sales records in Glasgow, picking the engine sales from between the binocular spare parts, I have that information.
The official debut of the 350cc production engine was on the 8th of October, 1921, at an unspecified “Motorcycle competition” in Ayr, where the machine (in AJS cycle parts) won four events and came second in one, of five events entered. The 350cc WA6 engine was introduced at the Olympia show that December. At the 1922 Olympia show, the 500cc WA7 and 1,000cc WA9 V Twin were introduced.
In total, about 1700 motorcycle engines were made. Most of these, around 1500, were 350cc. There were a few variations of the 350. All but a small few were WA6 or WA6A, although what the difference is, I can’t tell. Towards the end there were 30 or 40 WA6B, which had much improved oiling, and a small number of the “Octopus”, an 8 port race motor which plainly did not meet hopes. 120 of the 500cc WA7 engines were built, but only 80 of the 1,000cc V twin WA9. The last recorded sale was in October, 1926.
Armed with my new knowledge I wrote a few articles about Barr & Stroud for local Clubs and the like, and generally became a Barr & Stroud nutter.
At the time my main vintage motorcycle interest was with New Imperials, but gradually the interest in them waned as the fascination with Barr & Stroud rose. The Imps were all sold off, bar one; a 1926 350cc dog-ear JAP engine, with gearbox and rear wheel of a New Imperial factory racer mounted in a 1929 New Imp frame of the pattern used in their 1928 TT entries. A New Imp racer – bitzer, for which the dry build was pretty well advanced.
Then I was offered what was described as a 500cc Barr & Stroud engine that had been found in a wreckers/breakers yard in the USA. By my reckoning Barr & Stroud only made 120 of these engines, so I jumped at the chance to have a spare and bought it unseen, not even a photo. It arrived in soon after, fabulously well packed, but better than that, in spectacularly good condition. The inlet and exhaust manifolds were gone, but the magneto was still with it and no fins were damaged.
I stripped it for a look inside. Despite having had water in it at some stage, all was good, except the large diameter roller bearing that carries the sleeve shaft gear. This was a custom bearing in the day, but I was able to get a modern sealed roller of larger ID and smaller OD which was adapted to fit.
In both the 500 and 1,000cc B&S engines, the mainshaft pinion drives an identical sized idler pinion, which in turn drives the sleeve shaft gear at half crankshaft speed. That drives the sleeve. B&S made these idler gears from fibre, so they’d strip in the event of a seizure and protect everything else. Problem is that the fibre was a bit too soft. Ever Onward’s stripped and was replaced with an aluminium one long before it came to me, but the spare engine had a brand new bronze one. Not a wear mark on it, which made me suspicious.
B&S engines don’t have timing marks, so are assembled from first principles, with the timing set by the insertion of the sleeve driving gear. I reassembled the engine but could not get the timing anywhere near workable. Then I looked at Ever Onward. The exhaust exits right, but my new engine had a left exit exhaust. I lifted the cylinder, rotated it 90* to give a right exit exhaust, and hey presto! Port timing that works! I surmise that whoever went to fit the new bronze idler had the cylinder on wrongly, so could never make the engine run, hence it was discarded.
So now I had a complete, serviceable engine with vapour blasted crankcase and freshly painted barrel sitting in a stand on my bench. One rainy day I looked at the racer project, and you know what happened next.
The B&S engine fit neatly into the Imp frame, and a spare heavyweight New Imp gearbox squeezed behind it. I made some engine plates. New Onward was born. The dog-ear and its gearbox found a new home.
There was no primary drive, nor clutch, and a standard single plate New Imperial clutch would have struggled with the torque, even if I could get one. A mate suggested that such a silent engine needed a silent primary, hence a belt drive. The lights came on. My centres were so close to those of a pre-unit Triumph as does not matter, and the large New Imp main-shaft could be ground to accept the Triumph clutch centre. So it was and did, and in addition to my silent belt primary drive, I have a solid multi-plate clutch that will easily handle the torque. Not cheap, even using second-hand bits, but a very good and complete solution.
The rest of the build was straightforward, with one exception. I’d already had the tank painted, at great expense, as “New Imperial”, and it would need custom work to become “New Onward”. My mate of a mate signwriter who had done the B&S logo for Ever Onward was actively not interested, but in a lovely turn of events, Ross Leopold of Pep Signs lettered the tank for me by hand, matching the New Imperial lettering style. See the result; fantastic! His father, Guy, had done Ever Onward’s tank 55 years previously.
After some messing with ignition timing, New Onward fired and ran at the first attempt (but not the first kick!) on 15 April, 2021. It has a pre-war Type 76 AMAL which I’d set as for a Big Four Norton, which with a slight tweaking matches Ever Onward for performance.
Now it starts easily and rides nicely, sitting happily on 40 – 45 MPH, and pulling well on hills, taking nearly all in top gear. The exhaust note is decidedly woolly, without the ‘crack’ of most four strokes, but the silence is imposing. You can hear the magneto chain.
And then we come to the obvious question. Why didn’t the smooth, silent and torquey single sleeve valve engines catch on? There are two answers to this.
First is lack of development. Barr & Stroud were precision optical engineers who made binoculars, rangefinders, periscopes and the like. Business vanished with the 1918 Armistice, so they ventured into the proprietary engine business. By the mid 1920’s the precision optics business was coming back, plus they had other related products, and so engines were dropped. The single sleeve valve engine had it’s heyday in large aero engines; Bristol Centaurus, Rolls Royce Crecy, Napier Sabre, all rendered obsolete by jet turbines. Consider, however, that despite literally millions of engineer-hours over more than a century, poppet valves are still the weakest part of a modern internal combustion engine. Remember lead?
Second is insuperable. The oscillating elliptical path of the sleeve spreads lubricant perfectly, and necessarily wipes a film of oil on the ports at each pass. Some is drawn in and burned, some is blown out the exhaust and part burned by the hot gasses. This was not an issue in an earlier time, when total loss lubrication was standard practice. And that brings me to the big issue; lubrication.
Original fitment for Barr & Stroud was a Best and Lloyd oil pump. These were adjustable down from a quoted maximum 500ml per hour at 1000 rpm, but pump way too much oil for the Barr & Stroud engine.
Barr and Stroud weren’t engine designers, so started from a clean sheet. Unlike every other motorcycle engine of the era, the crankcase is one piece, as with cars. Within the crankcase are two substantial mounts for the main bearings. A packed gland seals around the main-shaft where it exits at the joint between crankcase and bottom cover, but the entire timing side is enclosed. Of course, the sleeve is fully enclosed, so apart from the breather, there are no openings to atmosphere.
The engine is oil tight to modern standards. Over-oil any other engine of the period, and oil belches out where it can escape.
But what if you don’t have cam followers or other openings to the atmosphere? Where does the excess go?
In a Barr & Stroud single sleeve valve engine, it accumulates in the engine bottom cover until the eccentric flywheels dip into it for a smokescreen of battleship proportions until the plug fouls. Prior to that point it runs with only the faintest hint of blue in the exhaust, just like any other motorcycle engine of its day.
Ever Onward was originally fitted with a Mk II Best & Lloyd pump. With this set perilously close to off, it still over-oiled terribly. It now runs a Pilgrim, but after each run I remove the drain plug and drop the surplus oil out. It can’t all get out through the exhaust.
One of the best documented and most widely repeated tales is that of Philip Brown and his Brough Superior outfit with a 1,000cc B&S V twin, who seized the engine one day in Dorset whilst trying to cut back the oil to reduce the smoking. He should have stopped and drained the crankcase. His wife had to help push the ruined outfit four miles to a garage, and I’ll bet he never heard the end of it.
an article by John Ferguson for The Girder Club
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