Power in Every Pulse: HONDA CB1100F Custom by Tajima Engineering

Tajima Engineering's CB1100F

This bike, named the CB1158RS, is based on the Honda CB1100F, as you can guess from the “CB” in the name. It’s the fourth bike in Tajima Engineering’s custom “RS Series,” which they began producing around 2010. The name “RS” comes from the Honda RS1000 racer, which was also based on the CB-F. For this bike, the exterior design follows the RS motif. It also has an additional subframe running from the frame neck to the swingarm pivot, reproducing the double-cradle frame of the RS1000. The number between CB and RS in the name indicates the engine’s displacement or base model — in this case, 1158. Let’s hear more details from Mr. Murashima of Tajima Engineering.

“The third bike in the RS series was built from a six-cylinder CBX, so this fourth bike is actually the third CB-based one. The exterior and subframe are inspired by the RCB/RS, but the frame reinforcements and chassis setup are basically the same as our CB-F customs.”

For this CB, which uses modern 17-inch tires, they added reinforcement bars under and behind the engine that connect the left and right sides of the frame, and they also added a plate under the neck area. The fork offset was shortened to secure a 100mm trail — which is their target value for stable and neutral handling, based on many previous builds — and this package has been well established as the standard for 17-inch conversions. The subframe can be removed, and with the exterior and headlight swapped, the bike takes on the appearance of a more typical CB-F 17-inch custom. For previous bikes, they have built engines using CB900Fs and CB1100Fs as the base, and in CB-F builds, the maximum displacement is generally known to be around 1123cc (using a 72mm bore, enlarged by 2mm from the CB1100R’s 1062cc). But this bike is different.

“As the name CB1158RS suggests, this one is 1158cc. When we built the first RS bike based on the CB900F, Mr. Tajima (the founder of the company, who passed away in 2022) and I decided to push the displacement as far as we could. We used pistons from the Honda XR250, which are 73mm in diameter. The XR pistons are designed for radial valves, so we modified them to fit the CB. It produced a lot of power. Later, when we sold that first RS bike, we swapped in a more standard 900-spec engine and kept this 1158cc engine in storage.”

For this fourth bike, the owner was someone from the CB generation who understood powerful bikes and knew about Mr. Tajima’s activities — such as running a motocross team and tuning bikes — back when he himself was riding motocross during the CB-F era. He had also ridden a BMW S1000RR before, so this engine was installed in the bike.

“We also mounted the front cowl a little higher than usual so it offers better rider protection at higher speeds. From here, we’ll take it to the Autopolis track, fine-tune it, and get more feedback from the owner.”

Both the engine and chassis are built entirely for performance. Even when they developed the first RS, they collected a lot of data from long-distance riding and from using a larger oil tank with double the normal capacity for durability. The expertise from their CB-F customs is also used here — from lightening the crank to modifying pistons and ports — all of which have already been proven and well received by many users. That history is what allowed them to create this 1158cc version. It will be exciting to see what new techniques and refinements are added to the RS package in the future.

Handlebar

From this angle, you can clearly see the front cowl bracket. The steering stem is from a 2008 CBR1000RR (SC59), with the fork offset changed from 45mm to 27mm. A one-off carbon panel holds three meters: a STACK ST200 (tachometer), an ACEWELL ACE-153 multi-function digital meter (which displays speed, distance, and other information), and a Yoshimura PRO-GRESS meter.

Bodywork

The front cowl with dual headlights is a commercially available RS1000 type. The cowl bracket is made from aluminum and mounts the cowl, but unlike other Tajima RS bikes, this fourth bike has it set slightly higher. Many parts, including the front master cylinder (NISSIN) and mirrors, use Honda stock parts, creating a production-bike-like atmosphere even in the hardware.

The fuel tank combines the upper half of a stock RC30 (VFR750R) aluminum tank with a lower half that is hand-shaped from aluminum to fit the CB-F frame, and welded together. The Y-shaped pipe visible under the tank is an additional aluminum subframe that gives off a wide double-cradle look. It is made from 7N01 material and serves both as an RCB/RS-style design element and as auxiliary reinforcement. It is lightweight and easy to attach and remove with just a few bolts.

The single-seat cowl, like the front, is a commercially available RS1000 type. It uses Dzus fasteners for smooth and quick removal. The taillight is round, taking inspiration from the RCB/RS endurance racers.

Engine

The engine is based on a CB900F/1100F (69mm stroke), combined with modified 73mm XR250 pistons to create the 1158cc spec. It includes many of Tajima Engineering’s proven modifications, such as crank lightening and intake and exhaust port work. It also has an original generator kit for the CB, providing ample electrical power.

The carburetor is an FCR 39mm. In this shot, you can also see how the Y-shaped subframe is mounted — it is fixed to the main frame at the pivot, under the rear of the tank, and at the back of the head pipe.

Chassis

The front forks combine extended inner rods from a CBR1000RR (SC59) with outer tubes from a VTR1000SP-1, creating a Tajima special with secured overall length. Both the front calipers and discs are SC59 stock components, with the calipers being TOKICO 4-piston radial type.

The wheels are SC59 stock, sizes: 3.50–17 front and 6.00–17 rear. The rear brake caliper is a Brembo 2-piston. The step plates and exhaust are Tajima originals.

The swingarm is a modified CB400SF (NC39). The front and rear chassis components, based on SC59 and other stock parts, are a standard Tajima configuration. The rear shock is an Aragosta, set up with Tajima’s data. The drive chain uses an EK ThreeD in 520 size.

Gallery

Specifications

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