1927 REX-ACME BLACKBURNE

Mitchell Barnes in Australia sent these photos of a 1927 Rex-Acme with a Blackburne engine. Can't tell yet whether it's a 250cc or 350cc, but given the size of that TT Amac carb, I would guess 350cc.

Rex-Acme were the little factory that could, winning the Isle of Man TT in '25 (Lightweight and Junior) and '27 (Junior), winning second and third places in '22, '23, and '26 - quite a record for such a small concern. Their 1927 TT-winning machine (Wal Handley aboard; see photo of him in the '27 Junior TT - special thanks to ace web researcher Dave Martin) would have looked very much like this motorcycle, as factory 'specials' of the period amounted more to carefully tuned standard bikes, than unavailable-to-the-public racers which were shortly to appear on the scene, and change European motorcycle racing in the 1930's (as had happened on US board tracks in the 'teens).

These Blackburne engines were surprisingly robust, belying their delicate appearance. Look at the period photos of a dismantled engine, which show the sturdy castings and well machined mating faces... no wonder these little engines did so well against much larger factories in the mid and late 1920's.

The b/w photo of the opened crankcases shows the interesting flywheel assembly; they're not simply a pair of discs, but shaped and polished, and the mainshafts are huge. It looks like they're still using crowded roller main bearings though, which aren't the best at higher revs (and unpleasant to assemble...). The cases themselves are cast very thick, with hefty bosses for the engine bolts. The crank discs are surprisingly robust for a machine which also has an EXTERNAL flywheel; that's a lot of spinning mass to dampen vibration, and Blackburne engines are renowned for smoothness.

The color photo of the flywheel is from The Classic Motorcycle (Nov. 1983) and shows a very similar machine, although if you look closely, 'our' machine has a an oil tank rather than a toolbox, and that TT carb, both signs of racing heritage. The gearbox is a 3-speed Burman item, the front forks are double-damped Webbs, same as used on Nortons and Velos of the period.

The cylinder head is also an interesting case - the valves are so large they break the bounds of the combustion chamber and the top of the barrel. It was clearly necessary to chamfer both the edge of the cylinder barrel and the spigot recess in the head for proper gas flow. A consequence of a long stroke (the 250cc engine is 60mm bore x 88mm stroke) is a small combustion chamber, as for a given engine capacity, the longer the stroke, the smaller the bore tube (and hence combustion chamber), and vice versa. Short-stroke engines have larger combustion chambers, making possible much larger valves for a given engine capacity. The Blackburne engine has cheated a bit by fudging the edges for larger valves - clever. As the spigot itself is almost completely chamfered away under the valves, I wonder if they have problems with compression leaks? I would assume the head is lapped onto the barrel with no head gasket, but a little gasket cement for luck.

If you have an interest in Rex-Acme motorcycles, and are looking for other Rex articles, try Classic Bike Mar. '85, and Classic Motorcycle, Aug. '90. There are more recent CB articles on Rick Parkington's Rex (he writes for the magazine, and is a ray of hope there), and Rick can be found hosting the Classic Bike Forum. It's time somebody wrote the book.

[A note on the video; it's a repeat of the video from my earlier post on the Rex-Acme, but I'm fairly sure this is the very same machine as above; the youtube caption says the Rex is in Australia.]

REX-ACME BLACKBURNE

I was inspired by the previous post to research the Rex-Acme marque, since Bernard Hieatt was racing such a machine at Brooklands. Rex-Acme motorcycles were renowned for a short period in the 1920's (say '24-28) for producing some of the most formidable racing motorcycles in England. Lots of success at Brooklands and in the Isle of Man (courtesy of Wal Handley) meant that this tiny manufacturer had great stature in the Vintage period, and the machines are now terribly rare and coveted.

Such was their racing pedigree, they used as their logo the Isle of Man triskelion on their logo (the Latin motto for the symbol - quocunque jeceris stabit; 'wherever you throw me, I stand' - the image is used in Sicily as well. Wiki claims a Celtic origin, but surely the invading Romans had a hand in it's design - triskelion is a Greek word anyway!).
I've seen a few at events around the world (although never in the USA), and none look remotely similar, such was the bespoke nature of their build, combined with years of mechanical changes for competition.

The top two pix are from the Banbury Run in 2007; the bike is a 1927 350cc Rex-Acme with a Blackburne engine (as all the racing bikes seem to have), belonging to Christopher Pierce. I note the Velocette positive-stop shifting mechanism on the gearbox; I think this bike used to belong to Brian Wooley, former editor of the Classic Motorcycle. Brian's bike had the same scalloped Velocette front brake as well. There is an article in Classic Bike from March 1985 which shows this machine, 23 years ago, in Brian's hands, reminding us that we are only custodians of these machines.

Next pic is from British Only; it's a 1928 500cc Blackburne-engined model, which was previously raced in Austria at some point; take a gander at the 'before' pic, which is pretty daunting. To be honest, the bike isn't well restored at all, and is going to need a better job done, with correct inverted levers and properly-fitting mudguards, and some decent paint and plating. The bike is too good to have a half-hearted job!
The 'before' pic shows an interesting feature of the Blackburne engines - their external flywheel. I'm not certain why they used this, as there is a complete set of flywheels inside the crankcase, but I understand that these engines are exceptionally smooth running, so perhaps the outside wheel dampens vibration. Another odd detail is the use of a crowded-roller drive-side main bearing, and a plain bush on the timing-side main... not a recipe to inspire confidence, but it obviously works well here.

The bottom two pix show a Rex at the Brooklands Reunion meeting in 2005, which has a similar early-style saddle tank as above. These first saddle tanks tended to be slab-sided and kind of squared-off, and were usually used for long-distance racing at Brooklands etc. You can see similar designs used by AJS and Sunbeam around this same 1926-28 period (George Cohen has such on his Norton sidecar outfit, too). It looks like this machine is ridden as well, as the owner has bothered to put a small silencer on the exhaust pipe. The carb is a later TT Amal, which I'm sure works better than the original Type 26 Amal track carb, which had no needle and was meant for full-throttle work only.

Here is a youtube video of a Rex-Acme in action! This is Martyn Adams with his 350cc ca '26 Rex.


I'm still researching Blackburne engines!

Here is a list of published articles I've found on Rex-Acme; contact me if you find more, and I'll add them to the list:
Classic Bike, Mar '85
Classic Motorcycle, Aug '90
Classic Motorcycle, Nov '93
Classic Motorcycle, Nov '04
'Historic Racing Motorcycles', J Griffith, '63, Temple Press
Plus, Rick Parkington has been chronicling an affair with his own Rex.