Honda XL250 Trailblazer
Check the specification of any modern 250cc enduro or motocross motorcycle (and many road going 250s) today and there is a certain similarity – all single cylinder, double overhead camshaft, four-valve. Just like the Honda XL250 of 1971. Sure, water-cooling is universal whereas the Honda used good old air, and twin cams replace Honda’s signature single camshaft, but otherwise not much has changed.
In the dirt bike boom that began in the late ‘sixties, Honda got hammered, mainly because the company’s ethos was four stroke technology, and virtually all the opposition was two-stroke based, not least being the ground-breaking Yamaha DT1, the motorcycle that brought trail riding to the masses. But Honda wasn’t ready to abandon its principles, not yet anyway, and quietly plugged away in the design department while others racked up impressive sales figures. Along the way, Honda refined what were essentially converted road bikes (the CL series) into more dual-purpose models, of which the SL350 was the first decent attempt and in retrospect, wasn’t a bad bike at all, albeit overweight. There was also the fine line of little off-roaders, namely the Honda SL125 single (which actually won a Gold Medal in the 1972 International Six days Trial ridden by American Leroy Winters), but what was desperately need to compete with the DT1, and to a lesser extent the Suzuki Savage (plus the Spanish Bultaco, OSSA and Montesa) was a proper 250 single that was as comfortable in the dirt as it was on the tarmac. In January 1972, it all came to pass, when Honda finally pulled off the wraps of its XL250 Motosport at a dealer convention in Las Vegas. The XL250 owed nothing to its predecessors, it was all-new, as was the XL designation that was destined for a long life. Honda did not appear to be overly worried that up till now, XL had been firmly identified with the Harley-Davidson Sportster lineage. Unlike previous Honda practice, the new engine was way oversquare at 74mm x 57.8mm bore x stroke, creating an engine that was not overly tall – a characteristic of most but not all four stroke singles with their bulky cylinder
head structures. The big bore also meant a big combustion chamber, and using single inlet and exhaust valves would have meant these items being weighty. Additionally, it would have required long and also heavy rocker arms to reach the valve tips, both of these factors limiting the engine’s ability to rev freely. Honda’s answer was to utilize its vast experience in racing, and to use four valves instead of two. This meant lighter valves that soaked up less heat, and shorter, lighter rocker arms operating them. Additionally, the spark plug could sit where its flame travel was at its optimum, right in the centre of the combustion chamber. All this technology comes at a price of course – the traditional tussle between the design engineers and the accountants – but Honda managed to keep the peace. The two-lobe camshaft itself was very short and driven from the crank by a conventional chain. A single rubber-mounted 28mm Keihin carburettor was used with twin cable operation for the round slide, feeding a single inlet port which split internally to feed each inlet valve. Honda also paid particular attention to air filtration, feeding air through several stages into a box containing an oil-impregnated polyurethane foam sock stretched over a fine-mesh stainless steel base. With the knowledge that a goodly proportion of XL250 production would end up churning through Californian desert trails, this attention to air purity was well founded. On the exhaust side, both ports from the exhaust valves Siamesed to a single 30mm outlet with a high level exhaust pipe leading to a fairly voluminous muffler with a small single outlet on the upper edge. Within weeks of the XL250’s release, several manufactures were hard at work on after-market exhaust systems, and although invariably louder than the standard item, few were any more efficient. Other aspects of the power-plant were fairly conventional, with a flywheel alternator on the left end of the crankshaft with the contact breaker and auto-advance upstairs on the end of the camshaft. The crank itself ran on roller bearings, with primary transmission by straight-cut gears to the five-speed gearbox and seven plate clutch. A high-capacity trochoid-type oil pump forced oil throughout the engine and gearbox, with internal screen and centrifugal oil filters to remove impurities. Visually, the engine’s unique feature was the use of die-cast magnesium alloy for the outer engine covers, which were finished in a unique shade of grey/green. The entire engine/transmission package was an exercise in compact efficiency, and looked little larger than the two-stroke singles it was intended to take on in the showrooms. Like the engine, the XL250’s chassis was all-new; a conventional single front down-tube frame splitting below the engine to form a cradle that then housed the swinging arm pivot. Up top was a large diameter backbone tube running down to the rear engine mount, the tube doubling as the oil tank. For a 250, the frame itself appeared to be overly engineered and excessively heavy – a point not lost on several US frame makers who quickly drew up lighter and better handling versions. Up front sat a set of forks that used a new-for-Honda style of damping, similar to the Italian Ceriani central piston system, with rear dampers each carrying two springs of different winding and five-way pre-load adjustment. Curiously, the rear shock had two upper mounting positions, the forward one about 50mm from the rear and slightly lower. Honda also abandoned its traditional full width hubs for new conical shaped items. The front had an aluminium brake drum, with a steel spoke carrier riveted to the flange on the right hand side, while the rear was a spool type with a built-in rubber shock absorber. Both wheels carried a new style DID shoulderless aluminium alloy rim; 21 inch front and 18 inch rear. Both mudguards were of lightweight flexible plastic, with a steel fuel tank and a steel base for the seat.
With durability a strong consideration, there was no way the XL250 was going to match the twostrokes in the overall weight department, and ready to roll, the weight was around 130kg, or around 20kg more than its arch rival DT1 Yamaha. The XL250 came with adequate lighting, turn indicators and instrumentation via separate speedo and tacho.
All these components could be quickly removed for weekend club racing. The seat, while basically designed for one person (rear footrests were fitted as standard), was wide and plush. In Australia, the new XL250 was received with enormous anticipation and translated into instant success on the showroom floor. As always, the bureaucrats fiddled with the standard specification, which meant a lower front mudguard had to be fitted before the machine could be registered in New South Wales. A major enticement for the two stroke riders was the XL250’s incredible spread of power, pulling smoothly from 1500 rpm with bags of usable torque in an engine that also had a healthy appetite for revs. Dealers were soon clamouring for more stock – the XL250 became one of the biggest sellers in the range. Just one colour was offered; silver with contrasting maroon and black striping. The basic model remained in production until 1985, an incredible run and a testament to the soundness of the original design. More than a few XL250s quickly found their way onto the track, as well as in the growing sport of Enduro. The quickly removable lights and instruments meant the XL could be ridden to the track and quickly stripped for action. The front fork stanchions could be slipped up or down in the steering crowns which helped in Short Circuit racing. The XL’s slight weight penalty worked against riders in motocross, but that didn’t stop quite a few trying. Not surprisingly, a huge range of after market parts sprang up; exhaust pipes, carburettors, air filters, mudguards, complete frames, and internal parts such as valve springs, camshafts and big-bore kits that took the capacity beyond 300cc. Even with the boosted performance, the original bottom end rarely gave trouble, although one hitch that showed up in competition was a tendency to break the gearbox mainshaft under extreme going, something that never affected the bike on the road.
MAIN/ABOVE Tim Margin’s restored XL250 at the Tamworth Lookout during the 2018 VJMC Annual Rally. Original Honda XL250 brochure extols its virtues.
ABOVE Motocross stars Roy East (1) and Brian Martin in close company on XL250s at the Amaroo Park circuit in Sydney in 1972. East’s bike has the NSW registration low front mudguard. TOP LEFT Cylinder heads under production in the Honda factory, with an XL250 4-valve head in centre of photo. LEFT Fresh off the production line; a batch of XL250s at the Honda factory in 1972. A restored XL250 owned by VJMC member Graeme Dusting.
LEFT A local ad for the XL250 from 1972. The man performing the jump is Bennett Honda NSW Sales Manager George Pyne, who was a handy scrambles and dirt track rider.