Sinroja Motorcycles CB590
By Ross Sharp - 01 Feb 18
It's been a seriously busy time for Leicestershire based custom shop Sinroja Motorcycles as last summer saw the 2-wheeled Goliath of a brand Royal Enfield commission bikes for the summer show circuit. Once the fanfare, stress and travel commitments ebbed the brothers found time to complete a few slightly more traditional projects that'd patiently vied for attention. In a break from the BMWs upon which they made their name, the Sinrojas let loose on this Honda CB500 bitsa special. The frame is actually from a CB550, well, the headstock and cradle is. Everything rearward from there was replaced by new subframe tubing, with pillion peg mounts, running at the same angle as the bottom of the fuel tank, apart from the subtle kicked-up loop. A partially cross-stitched saddle long enough for two follows the sleek lines, the leather an offcut from a local Bentley upholsterer. As with all Sinroja builds the motor is completely back-to-the-crank fresh, although now enlarged from a 56 to 61mm bore giving 590cc of punch. Domed pistons from America ramp the compression up from 9:1 to a heady 11.5:1. The original head was missing so a surragate from a CB650 was fitted - modified of course with new valve seats, valves and a high-lift cam. Carbs from a Kawasaki Z650 up-jetted for K&N pods are the final piece in the jigsaw puzzle meaning this fruity four-banger should make a healthy and pointy curve on the dyno sheet, especially now it's running the Sinrojas unique Pulse Jet Ignition plugs - see here.
The exhaust looks particularly neat, because it is. Four CNC mandrel-bent stainless headers collect and exit through a single Cone Engineering silencer. It must crackle and howl nicely with all that extra fire in its belly.
Towzatronics ran a completely new wiring loom utilising a Motogadget M-unit box and keyless ignition. Switchgear and barend indicators are also from Motogadget but the rear are combined brake and flashers from Rizoma. The headlight is a classic Reno 7 incher.
Fastec Engineering machined a new but traditionally styled top yoke to incorporate a Motogadget Motoscope Tiny. The forks though is stock, almost. An additional caliper and period correct solid disc will balance the engine's extra shove. Adjustable aluminium clipons with internally routed wires and Domino throttle complete a neat cockpit. Flanged aluminium Akront rims and stainless spokes shed a few vital grams and replica Firestone tyres adhere to the now traditional café-brat style.
The paint job is adds a subtle flair. A deep gloss black with 24 carat gold nano particles (expensive metalflake) was chosen for both the tank and frame, meticulously painted by GD Design in Northants. Under the right light the flakes are just visible - see the subframe above. 24 carat gold Honda wing badges replace the cheap, original stick-on logo. A machined ally knob fastens the gold standard tank cap flap, which now wears a gold Sinroja emblem.
Rather than being a commission for a customer this sharp looking CB is actually up for sale to pave the way for new projects, some of which we hope to see unveiled at Bike Shed London 2018 this May.
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Images by Ivo Ivanov