4 Valve Engine Bikes

[Bran Cardello]

Theolder model had smaller intake valves, which means less weight bashing against the head. It also has 3 rings compared to the newer models 2 ring piston. I'd have to believe it's more reliable, but the newer model may have better engineering.

Both my 5 valves were bulletproof, but you have to remember too that engine had alot of years of development and retooling, it wasnt perfect from the start and neither should anyone expect the same from the new bikes. I will say though they seem to be every bit as reliable, my 2014 had 75 hours on it and valves still in spec, my 15 seems to be following the same route. Sure there are little things (water pump impeller update, shift stopper, etc.) but Yamaha stands by their products and knows people buy their brand based on reliability. Personally the new bike is leaps and bounds better than the old bikes, do yourself a favor and try a 14-15.

My 2006 yz250f still has the original valves, replaced a top end and a few cam chains for reassurance but it's a reliable as they come, my 2012 450 is a 4 valve design and it seems to be tough too! Yamaha seems to make a nearly bullet proof engine compared to other manufactures.

From what I hear from people with the 14+ 250f...it is a lot more powerful then the older gen. I haven't ridden one...so I dunno how it compares to my bike which is an 07 269f. They say it turns a lot better too. I would assume it will have similar valve durability assuming you perform maintenance timely and correctly. I know they have had little minor issues...but so far I haven't seen people saying the valves went bad in NO time. Even if I seen one person with valve issues early...I would likely assume (because its the internet) that they just dont know how to oil a filter lol. Now if I seen it all over the place by tons of owners at similar hours...then maybe I would question their reliability as far as top ends.

In short and just MHO the five valve engines are bullet proof in stock form or slightly modded. Go beyond that and in my personal experiance they arent as reliable or at least require more maintenance. Its also hard to compare the 5 valve to the new 4 valve as the 4 valve is on a FI bike. I have owned both and I love my new FI 4 valve. More than enough power for me but not so much (like a 450 FI) where I cant handle it when I get fatigued.

Among the many mechanical spare parts for motorcycles, the ones most in demand on the market are motorcycle valves. There are different types of valves available and each one meets specific requirements. If you need spare parts of any kind, you can rely on the Athena shop, a website specialized in the sale of motorcycle engine valves. The motorcycles valves that you can find on the website are manufactured by Athena, a leading company in the field of mechanical spare parts for motorcycles. The valves are made of titanium, a very compact and stainless material, and are perfectly stackable and can replace the original ones, increasing the mechanical performance of the engine, always ensuring maximum reliability. There are also intake valves that can be installed on the exhaust springs and seals. The valves also adapt to other components such as half-cones, seals and plates and offer the same mechanical stress strength as the original ones.

A choke valve/cable is designed to restrict the flow of air in the carburettor of an engine. This helps enrich the fuel-air mixture, improving the ability to start an engine in low temperature conditions.

For carburettor fitted bikes, a choke valve/cable helps ensure there is enough useable fuel to start the engine when temperature and climatic conditions are low. The ratio of air and fuel required to start the engine changes with temperature due to the physics and thermo-dynamics behind combustion and air density.

Each model and make of a motorcycle will utilise choke valves and cables slightly differently. Some motorcycles use a choke to reduce the airflow to enrich the mixture, while others use an enrichment valve that increases the amount of fuel (as opposed to reducing the airflow). Both types achieve the same thing but may be set up differently depending on the model and make of bike.

An EFI uses computers and sensors to better understand external conditions, helping to decide what the optimal airflow/fuel mix should be. This reduces poor performances but mitigates excessive fuel usage.

While some may prefer the hands-on approach of carburettors and manually controlling the choke, others may welcome a more automated approach. Whatever your preference, EFI systems are increasing in usage and popularity so are likely to continue to grow within the world of motorbikes.

Regardless of whether you are a traditionalist and are sticking to carburettors or just purchased a new bike with EFI, our range of motorcycle cables and products here at Venhill are designed to help you get more out of your bike. We ship our products to Distributors all over the world and sponsor some of the best MX and Superbike race teams in the U.K.

Honda returned to the 500 cc class of the World Motorcycle Grand Prix series in 1979, following a twelve-year hiatus. The machine they had developed for their comeback - an entry in the World Grand Prix's most prominent class - was the NR500, powered by a four-stroke, DOHC V-four engine. With its oval piston engine incorporating eight valves and two connecting rods per cylinder, plus an aluminum semi-monococque frame complete with an inverted front fork, the machine surprised everyone with its daringly innovative technologies.

"When I look back at it, I'm not sure if we were experimenting with cutting-edge technologies or obsessed with foolish ideas," recalled Toshimitsu Yoshimura, an engineer involved in the development of the NR500's oval piston engine.

"The emphasis was to create a difference-not just any difference but the difference that would work to our definite advantage. That's why we decided that Honda should go with four-stroke engines. We wanted to achieve our target through innovative technology, and in so doing have the edge over our competition."

Road-racing circuits were in those days dominated by bikes with two-stroke engines. Despite this trend Honda went with its NR500 machines equipped with a four-stroke engine. That decision, however, wasn't so much a bold move as it was a natural choice.

During its first years in motorcycle racing - dating back to a memorable entry in the Isle of Man TT Race - Honda won event after event with four-cycle engines. They achieved so much success, in fact, that four-cycle engines came to be thought of as a Honda specialty. Though two-stroke engines had the benefit of relatively higher output, nobody could stop Honda from wanting to develop four-stroke engines capable of producing even greater power. In that regard, the conventional thinking proved somewhat contrary at Honda. In fact, competing in the TT race was in every perspective an extraordinary decision.

Adding to the Honda preoccupation with four-stroke engines was the fact that many in top management, who had decided to make a comeback in the World Grand Prix series, and those involved in the development, were imbued with the philosophies of Soichiro Honda, who had criticized two-stroke engines as being little more than "bamboo tubes." To them, it was simply out of the question to reclaim their victory with anything less than a four-cycle engine.

Yoshimura, who had actually designed the engine, was from the very beginning a staunch advocate of the four-cycle approach. "Four-stroke engines," he said, "have distinctive mechanical processes. The (intake) valve closes tight, combustion occurs, the exhaust valve opens, and the exhaust is released. It's a sequence of independent processes, each with a different function, working together to facilitate the engine's entire operation. This is really fascinating, from an engineering standpoint. I believe this mechanism will be the basis of further advancement in engine technology."

Afterall there is no point in participating in a race if one isn't confident of victory. However, that confidence must come from hard work and the determination to stay the course through thick and thin. No matter how difficult the journey, one must continue as long as there is the slightest possibility of a positive outcome. It is in this very struggle that the value of one's endeavor exists. Honda engineers recognized how difficult the process could be, but ultimately they also knew success would be gratifying. Thus, the development team's decision to return to glory with four-stroke engines was most appropriate.

Honda announced its plan to go back to the World GP circuit the following April, 1978. Accordingly, a new organization called the NR (New Racing) Block was formed at the Asaka R&D Center for the purpose of developing racing powerplants. When the project began, the engine development team had only three very young staff members. But Honda had established key objectives for the resumption of racing operations. Assembling a young development team was very much in keeping with one such objective, which was to "foster young talent with the spirit of racing."

Yoshimura, who was only in his sixth year at Honda, didn't have any experience with Honda's past racing activities. Ideas such as "resuming racing activity" and "returning to the World GP circuit" had simply not crossed his mind.

"Instead of being excited about developing racing machines, our feeling was more akin to raw determination", he said, "It was the determination to create something that would represent the very best in technology. We were determined to create an engine to surprise the whole world. We believed that if we could create the best engine, it would bring us a victory."

The average output of Honda's rival two-stoke engines was in those days around 120 horsepower. Although horsepower isn't the only determining factor in a victory, the development staff knew they should first achieve a degree of power output exceeding that of the competition.

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