Optimizing the design of the TRX
Posted: Sat Aug 15, 2009 2:24 am
Although initially perceived by some as a brazen attempt to muscle into the Ducati 900SS market, the TRX has a number of clever design elements that give it its own special character.
First, is the choice of a parallel twin, flying in the face of the fad for V-twins. Most notably, the TRX has the innovative 270-degree crank. This is such a brilliant compromise between the 360 crank (even firing intervals, but poor primary balance) and the 180 crank (good primary balance, but an uneven rocking couple and uneven firing intervals) that "270" may become the standard for parallel twins. For instance, the new Triumph Thunderbird has been given a 270 crank. The TRX also has 5-valves per cylinder; and it's perhaps a shame that Yamaha didn't give the engine two spark plugs per cylinder (so easy to do with 5 valves).
Secondly, we see the clever adoption of dry sump lubrication, which was once the norm for the classic English twins. Although most modern bikes are wet-sump, it is generally agreed that, for a motorbike, dry-sump lubing is the better system. (The classic Honda CB750 of 1969 was dry-sump).
A clever innovation on the TRX is that the oil tank is not remote, but is integral to the engine, sitting atop the gearbox. This design eradicates external oil lines, allowing simpler engine installation and providing faster oil warm up. Crucially, a dry sump allows the engine to be positioned lower in the frame, optimizing the center of mass. In other words, having the oil tank high up, full of low-density oil, means that the really heavy bits of engine can be positioned lower. Inclining the engine forward some 30 degrees further helps; and having the centre-of-mass so low down is ideal for the TRX's handling and "flickability". Looking at the R/H engine case, it seems as if the clutch is very high up. Not really! It's just that the engine itself is so low. But....
.... But why didn't Yamaha go the whole hog? Even a dry-sump engine has to have a small sump for the oil to collect for scavenging; and Yamaha put the two header pipes UNDERNEATH this "mini-sump". If these pipes were splayed to pass either side of the mini-sump, the whole engine could have been two or three inches lower, with further associated benefits. The clutch and gearbox could then have been sited even further forward, giving a short, stiff, compact engine which would have allowed a longer swinging arm. Also, assuming that the heights of the seat, fuel tank and steering head would remain much the same, the lowered engine would give extra room under the tank for bigger components such as, say, a larger air filter.
I love my TRX. It's my 42nd bike; and while I used to change my bikes pretty often, I plan to keep this Yamaha for the foreseeable future. The TRX trellis frame, perhaps inspired by the 900SS, is a much stronger and stiffer item than the Duke's design. So ... if only Yamaha were to come up with an updated TRX900 with an ultra-low-slung twin-spark fuel-injected engine with modern suspension and brakes, such a Mark II TRX would be a winner! But it won't happen, will it?!
First, is the choice of a parallel twin, flying in the face of the fad for V-twins. Most notably, the TRX has the innovative 270-degree crank. This is such a brilliant compromise between the 360 crank (even firing intervals, but poor primary balance) and the 180 crank (good primary balance, but an uneven rocking couple and uneven firing intervals) that "270" may become the standard for parallel twins. For instance, the new Triumph Thunderbird has been given a 270 crank. The TRX also has 5-valves per cylinder; and it's perhaps a shame that Yamaha didn't give the engine two spark plugs per cylinder (so easy to do with 5 valves).
Secondly, we see the clever adoption of dry sump lubrication, which was once the norm for the classic English twins. Although most modern bikes are wet-sump, it is generally agreed that, for a motorbike, dry-sump lubing is the better system. (The classic Honda CB750 of 1969 was dry-sump).
A clever innovation on the TRX is that the oil tank is not remote, but is integral to the engine, sitting atop the gearbox. This design eradicates external oil lines, allowing simpler engine installation and providing faster oil warm up. Crucially, a dry sump allows the engine to be positioned lower in the frame, optimizing the center of mass. In other words, having the oil tank high up, full of low-density oil, means that the really heavy bits of engine can be positioned lower. Inclining the engine forward some 30 degrees further helps; and having the centre-of-mass so low down is ideal for the TRX's handling and "flickability". Looking at the R/H engine case, it seems as if the clutch is very high up. Not really! It's just that the engine itself is so low. But....
.... But why didn't Yamaha go the whole hog? Even a dry-sump engine has to have a small sump for the oil to collect for scavenging; and Yamaha put the two header pipes UNDERNEATH this "mini-sump". If these pipes were splayed to pass either side of the mini-sump, the whole engine could have been two or three inches lower, with further associated benefits. The clutch and gearbox could then have been sited even further forward, giving a short, stiff, compact engine which would have allowed a longer swinging arm. Also, assuming that the heights of the seat, fuel tank and steering head would remain much the same, the lowered engine would give extra room under the tank for bigger components such as, say, a larger air filter.
I love my TRX. It's my 42nd bike; and while I used to change my bikes pretty often, I plan to keep this Yamaha for the foreseeable future. The TRX trellis frame, perhaps inspired by the 900SS, is a much stronger and stiffer item than the Duke's design. So ... if only Yamaha were to come up with an updated TRX900 with an ultra-low-slung twin-spark fuel-injected engine with modern suspension and brakes, such a Mark II TRX would be a winner! But it won't happen, will it?!
Cheaper insurance too 
My van has got 6 FFS !
