Two Stroke Engine Rebuilding

2011 Aprilia RS4 125 | Review

Aprilia 125cc

I remember watching Mick Doohan winning 500GP races whilst Valentino Rossi, Max Biaggi and Loris Capirossi battled it out on the Aprilia RS 125s and 250s in the late nineties. This was the heyday for the 2-strokes.

In 2011 you can still buy the legendary RS 125 but the future is the RS4 125 that I've tested at the ASC Vairano circuit in the North of Italy...

Everybody knows that the 125cc 2-strokes are faster more efficient engines. The RS 125 can be tuned to around 33 horsepower whilst the RS4 125 can be tuned to around 25 horsepower as an 180cc bike.

Nobody at Aprilia is saying that the RS4 125 can replace the RS 125 performance wise because it can't. The RS4 125 benefits from a reliable 125cc four stroke engine that doesn't need a rebuild every 10,000 miles. The RS4 125 is also more environmentally friendly using less fuel and oil compared to the 2-strokes. All in all the RS4 125 is a much cheaper bike taking all considerations including running cost.

I tested the RS4 125 in learner legal version where 15 horsepower is available at 10,500rpm and 11Nm of torque at 8,500rpm. The 120km/h top speed enables safe riding on motorways and the engine isn't going to blow up after long runs at top speed.

The four-stroke torque curve enables cruising from 8,500 rpm and a very decent fuel range. I however tested on a race track so I spent pretty much all the time testing in the range between 10,500rpm and 11,000rpm where the engine pulls much better than anywhere else in the power range.

It's a narrow range for riding fast and I quickly found out that loosing revs must be avoided at all cost. Compared to a 2-stroke there's plenty of midrange though. I must admit that I had lots of fun racing the other journalists on the circuit and it got slightly boring as soon as I found myself without anybody to chase down. Just like they do in the 125 GP championship we slipstreamed each other to enable overtaking on the brakes.

And the brakes on the RS4 125 are very sharp consisting of a 300mm disc and a 4-pot radial calliper. I hardly used the 200mm rear brake at all as let's face it, the speed needed to be brushed of was never great and from top speed only 30-40 odd kilometres as I always needed momentum for as high a corner speed as possible.

The dry weight is a claimed 134kg (RS 125 approx 121kg) which is lightweight for a four stroke. Admittedly I'm quite large for the RS4 125 but on the pictures you could briefly think that I'm on the RSV4 rather than the RS4. The suspension is not adjustable and to my surprise Aprilia has found a good standard set-up as I had nothing to complain about chassis wise. I presume the small motorcycle handles even better with a lighter rider which I again presume most 16-year olds are. The tires are of sizes 100/80-17 front and a 130/70-17 rear.

Handsome Articles » The Great Debate: Two Stroke Vs. 4

The battle for supremacy between two stroke and 4 stroke quads is prone to rage on forever, besides for outdoor factors that may finish this age outdated debate; it is very doubtless that upcoming legislation may finish manufacturing of two stroke engines, making it unattainable to get a new two stroke quad. So for those who’ve ever considered getting a two stroke quad, the clock is ticking.

Mechanically the distinction between a two stroke and 4 stroke lies in how usually the spark plugs fire. In a two stroke, it fires once with each revolution of the cam, while a four stroke solely fires the plugs each different revolution of the cam. With every part being equal, a two stroke can have twice as many combustions as a four stroke, which causes it to provide rather more power with the same size engine. While this will likely make a two stroke sound like an obvious alternative, there are several drawbacks to the design and efficiency traits of two stroke ATV engines.

The additional power and warmth produced by a two stroke requires oil to be added to the gas to keep the engine properly lubricated. Because oil is put in the combustion chamber, stroke engines smoke rather a lot, which is the explanation for the imminent ban on them. One side effect of the spectacular energy that stroke engines produce is that the top end of the engine must be rebuilt considerably ceaselessly, depending on how hard the engine is pushed. Though the rebuild will not be terribly costly, it must be achieved periodically to keep away from rebuilding your complete engine.

For many riders the fixed upkeep is definitely worth the efficiency they get out of their stroke engine, however the accessibility of this power could also be prohibitive for some riders, driving styles, and terrain. In order to faucet into the power of a stroke engine, it’s important to keep the throttle close to wide open to stay within the energy band. Although some models are higher than others, some stock two strokes lack actual energy on the low or midrange. Within the palms of an experienced rider, a stroke is an incredible machine, but in certain situations, you can lose all of your energy by making a vital up shift or slowing down with out a laborious down shift. However, their explosive energy makes two strokes the engine of alternative for a lot of racers, particularly in racing disciplines that require frequent jumps and quick acceleration out of turns, reminiscent of Motocross.

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