Cut'n'Shut FFs

I spent a lot of time at the NEC show, peering under, taking pictures from the side and generally poking at various models looking for machines that would be suitable for the sort of quick and dirty FF I'm so fond of. Here's a few thoughts. For those of you more into ground up building, some of the engine comments are still relevant.

Honda Bros/Revere/GT650

This looks very straight forwards. The bike is narrow enough and the beam frame and low set suspension leave a big sitting area. The Bros has an ally frame with a bolt on rear sub frame so no major structural work would be needed. The front exhaust pipe would need some insulation to avoid burning one's leg although aftermarket pipes might remove this problem entirely. There looks to be room for a fuel tank between the engine and front wheel. Already uses a fuel pump. These bikes are still being made and are current in some markets, so can be obtained fairly easily. The Revere variant has a steel frame and would require a bit more hacking about, but also has a shaft drive.

Honda Firestorm

Although superficially ideal, the frame makes it very difficult to build an FF as some major surgery would be required around the seat area. The engine looks appealing for a special though.

Suzuki TLS1000

This thing looks just about ideal. A bolted on rear subframe and hi spec components. It remains to be seen if they will be reliable. Suzukis have not always been ok in there first model year. The rear suspension is weird with a rotary vane shock seperate from the rear spring. This will be a PITA for the racers but need not concern us. It's not clear if the EFI will be easy or hard to deal with and the effect of changing or removing the airbox may completely screw the carburation. Biggest problem would be finding somewhere to put the fuel tank. Both this and the Honda are very compact power units but still unproven. Curiously, they both have two cam chains, an area where they have both fallen down in the past.

Yamaha TRX

Again just about ideal. The basic frame is ok but some of the triangulation would have to be removed for the seat. I'm not clear how much would have to be put back to restore the strength. If you look from the side, You can clearly see how an FF could be built. Like the Bros, there appears to be room for a fuel tank, low down between the engine and front wheel. Already uses a fuel pump.

Kawasaki EX500 (GPz500) and Suzuki GS500

At the small end, both could be converted with relative ease. They are both definitely built to a budget but quite pleasant little bikes.

From all this, it can be seen that building an example of this style of FF has the same dominant build problems, no matter what the source bike.

A second steering head with drag link to carry the handlebars.
This is a vital piece and needs to be engineered properly. Get a local special builder to help if you're not confident yourself.
Forward footrests and foot controls.
Relatively easy with a drill, some dural and some second hand bits.
A fuel tank.
Again, there are quite a lot of people who can build fuel tanks. the problem is finding space for it.
Bodywork, lights and seat.
The hard part unless you are used to styling, design and grp.

To re-iterate another recent post, I can see how the above could be put together as a very DIY kit with a set of plans that said "cut here" and "extend the wiring loom there". It's probably not possible to make it a complete "bolt on" but you could get pretty close.

Less Suitable Donors

Triumph T595

I thought this would be fine. From the side, it looks as though there is room for everything, but from on top, you would have to spread your legs too wide to clear the frame rails. If you were building a new frame, the top of the engine is fairly narrow and the EFI is much more downdraught than the old engine, but the bottom end is still pretty wide.

Honda VFR750

The VFR series has a lot of appeal as the engine is fairly narrow and the standard frame and basic components are of high quality. Looking more closely, this is a very dense package and a lot of work would be required to relocate all the components that are packed round the bike. Looking at the basics, the engine is quite narrow at the top, but the alternator and clutch make the lower engine as wide as a current straight four. For an FF this is probably not a problem as this doesn't really encroach on leg clearance. The frame has a tidy rear suspension arrangement that leaves plenty of room for an FF solo seat. All the models have a bolt on subframe. The early '87-'90 model and '95 on models have no problems in the seat area, but the middle design had substantial frame extensions that are right where you would want to sit. Viewed from the top, the frame is actually quite wide at the back and might be uncomfortable as it fills space where your upper thighs want to be.

There's the usual problem with finding space for a tank. Like several Hondas, there is a big space behind and below the front wheel. This might need some adjustment of the exhaust and perhaps cooling ducts to the exhaust outlets.