For more than a decade we’ve ended the year with our Pipeburn Top Ten Bikes and picking the list is never an easy task, as we try to cull down so many magnificent machines to the final few. And of course, the public’s opinions will all differ wildly, getting a consensus is like trying to draw blood from a stone. So, when we sat down to pick our top ten list of the best engines from the custom bike scene, we knew we were taking on the impossible. This is not an exercise in choosing the most powerful nor best-engineered lump, but choosing the engines that have powered our scene, mixing reliability, budget, power and ease of use. Your comments are encouraged, and your brand loyalty is understood, it’s time to press the start button and fire things to life. 

Yamaha SR500 by Sane Motion Moto.

10. Yamaha SR500 – 499cc, air-cooled, SOHC, single-cylinder, 2-valve.
The ultimate simple single, cheap, with enough horsepower to have plenty of fun and with a pleasing mechanical aesthetic. It’s no wonder that this engine was front and centre of the cafe racer revival, powering a motorcycle that is the original modern classic, having spanned five decades of production in both 400 and 500cc form. Brilliantly reliable and a bargain to maintain, you only have to add a nice muffler and new carb to really bring this motor to life. The popularity of the SR in Japan alone means it deserves its place on this list, but in addition to the likes of Heiwa and Candy, Deus Ex Machina have built a global brand around this legendary lump.

Yamaha RD350 by Jake Shellito.

9. Yamaha RD350 – 347cc, two-stroke, air-cooled, parallel twin.
You can’t have a list of great engines without including the ring-a-ding-ding of a two-stroke and the three fiddy Yamaha gets the nod for many reasons. Sure it doesn’t make the horsepower of the Kawasaki products of the era but when you put loyalty aside, it’s a better prospect for a custom bike than any of its rivals. Tight and neat packaging, automatic oil injection, available with a six-speed gearbox and reed valve technology. It all adds up to a more reliable product that packs in plenty of fun and has powered a whole host of tasty customs. The fact that it’s so closely related to the GP TZ350 adds not only street cred but plenty of great off the shelf power parts too.

Royal Enfield Interceptor by Revelry Racing.

8. Royal Enfield Twin – 648 cc, air/oil-cooled SOHC, 8-valve, 270° parallel twin.
Less than ten years ago, Enfield set out to not only create an engine to power their fleet, but to be the ultimate in affordable modern classic motoring. To say they have succeeded is an understatement! A parallel twin with timeless good looks and an almost unbreakable bottom end forms the foundation. But a 270° crank, clever balancing shaft, smooth Bosch fuel injection and a slipper clutch also mean you’re left wanting for nothing. Thousands of customs have already been built on the platform, and the likes of Australia’s Revelry Racing have proven big performance is possible from an engine that can be the heart of any style of bike you can dream of.

Yamaha XS650 Cafe Racer by Purpose Built Moto.

7. Yamaha XS650 – 654cc, parallel twin, air-cooled, SOHC, 2 valve.
The development of this engine was started in the ‘50s by a company not named Yamaha, but by the time the Iwata factory launched the XS650 to its customers, it not only looked as good as any of its British parallel twin rivals, but it was far more advanced in its technology too. Of unit construction, with horizontally split cases and raced by King Kenny Roberts himself, it’s easy to see why the third Yamaha on our list gained such a following. The fact it looks at home in everything from a chopper to a flat tracker doesn’t hurt either. And perhaps most importantly, the aftermarket has kept it relevant with 277° re-phasing, trick carby kits and fancy electronic ignition.

Harley-Davidson Sportster ‘Dirtster’ by LC Fabrications.

6. Harley-Davidson Sportster – 1200cc, air-cooled, 45-degree, V-twin engine.
Sure it’s available in various capacities and bits and bobs have changed over the years, but no other engine comes close to powering as many custom motorcycles as the Evo. Loud, heavy and obnoxious compared to its counterparts from around the world, there is no logic to the big American’s success, other than the pure emotion it evokes as the torque and thundering sound makes you feel like you’re truly alive. She’s a handsome beast, the aftermarket is awash with parts for style and speed, and just like the muscle car, it will remain the working man’s hero long after electrics have taken over the world.

Honda NX650 Dominator ‘Baja Domi’ by Soli Moto.

5. Honda NX650 Dominator – 644 cc, single-cylinder, four-stroke engine.
The RFVC-equipped engine was designed to serve in a host of Honda applications, and it is this simple versatility that makes it so good. The Domi might have been a cheap urban trail bike, but with 53nm of torque in a lightweight package, it provided plenty of bang for your buck. And the engine has proven so bulletproof that it now powers an ever-growing group of cool customs. Few companies have ever produced as many good engines as Honda, so it should be no surprise that this simple single is smooth, punchy and cheap to run. It responds well to breathing modifications and for any dirt work or urban assault vehicle, it makes a hell of a lot of sense.

Triumph Bonneville ‘McQueen’ Scrambler by FCR Original.

4. Triumph Bonneville – 865cc, air-cooled, DOHC, parallel-twin.
The Bonneville is the most timeless name in British motorcycling, old and new, and in every iteration, they’ve all relied on that quintessential parallel twin. So, picking the best engine of the bunch really comes down to your budget and what you intend to use it for. But backed into a corner, the 865cc air-cooled variant gets the nod from me. It doesn’t have the desirability of the classic, nor the tech and power of the new, but it finds a way to blend the best of both worlds in a fashion nobody else can match. Great after-market support means more power is only a mouse click away, and their popularity literally saved the brand. Workshops like Spain’s Tamarit have built more than a hundred customs based around this engine and it’s hard to see them ever going out of style.

Ducati Leggero by Walt Siegl.

3. Ducati 900SS SuperSport – 904cc, air-cooled, desmodromic, 90° L-twin.
There is just something about a Ducati that makes you feel special the moment you climb onboard. And while the 2-valve 900 is neither the most powerful nor most prestigious of the company’s engines, it has proved to be the choice of customisers around the globe. A genuine Desmo engine, that pulls hard down low, has plenty of power up top and looks a million dollars doing it, you can’t help falling in love. The fuel-injected example is buttery smooth when properly tuned, or you can fit a set of flat-slides and awaken an angry beast. As the price of donor bikes has fallen, we’ve seen an influx of these Italians in our inbox and they simply never disappoint.

Honda CB750 by Cardsharper Customs.

2. Honda CB750 – 736cc, SOHC, air-cooled, straight four.
We don’t see them like we used to, but when the cafe racer revival took off, the CB750 was front and centre. The original UJM engine, a high-revving four-cylinder across the frame, they’ve inspired the sports bikes of the last 50 years and all the Japanese manufacturers and BMW still use the layout for their latest road rockets. If you want horsepower in an old-school build, this is one of the engines to have, the parts are plentiful, the aftermarket has everything and they’re as reliable as anything on the road. The engine has found a home at the centre of the cafe craze, while also powering drag bikes, choppers, road racers and so much more.

BMW R100 by Wedge Motorcycles.

1. BMW R100 – 980cc, air-cooled, laterally opposed boxer twin.
The famed Boxer engine goes back to the beginning of the BMW brand’s entrance into the world of two wheels, but it is the air-head range that powered the R series for so many years that makes it to the top of our list. In stock trim, few other motorcycle engines have ever been as reliable, now or then, and that smooth torque is simply a smile a minute. But these motors can also be seriously hopped up, from big bore kits, to the supercharged R of F1 engineer Ben Norton, to the twin-turbo version of Boxer Metal that hammered down the 1/8th mile at the Glemseck. WalzWerk sells them in their hundreds and there is barely a shop out there that hasn’t taken an R series and made something special. The look is not to everyone’s taste, but you just can’t argue with the impact this engine has had on our scene.

Clearly there are a lot of brilliant engines that just missed the cut, like the Guzzi V-twin and the Kawasaki Four. So, tell us, what’s your favourite engine for a custom and which mighty motors would have made your top ten list?