RCB E2 SERIES BRAKING SYSTEM
Recommended Additional Upgrades
01
Uma Laser Iridium Spark Plug
Improve ignition with Uma Racing Laser Iridium Spark Plug.
03
Uma Racing Engine Oil
Get smoother engine performance with Uma Racing Full Synthetic Engine Oil.
The UMA Racing Adjustable Timing Gear (also referred to as an adjustable cam sprocket) is a high-precision valvetrain component designed for the Yamaha 155cc VVA engine found in the R15 V3, R15 V4, and R15M.
While electronic tuning via an ECU alters fueling and ignition spark parameters, an adjustable timing gear gives engine builders physical, mechanical control over the camshaft’s orientation relative to the crankshaft. This allows you to shift the engine’s powerband to suit specific track or street requirements.
Key Features
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Precise Mechanical Cam Timing: Allows for a adjustment range of 5(+/-) degrees. By advancing or retarding the camshaft alignment, you can manually dictate exactly when the intake and exhaust valves open and close.
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Shift the Powerband:
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Advancing the timing shifts the engine’s torque and horsepower lower down the RPM range, improving bottom-end acceleration and throttle punch.
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Retarding the timing pushes the power band higher up into the rev range, optimizing the top-end speed and high-RPM over-rev.
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Integrated Decompression Function: Features a built-in decompression mechanism/pin structure identical to factory specs. This reduces cranking compression momentarily during startup, ensuring smooth, easy engine turn-overs and preventing strain on the starter motor (critical for high-compression big-bore builds).
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High-Grade Carbon Steel Construction: CNC-machined from ultra-durable carbon steel alloy to increase rigidity and structural stability under extreme physical stress.
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Secured Fitting & Anti-Slip Design: Redesigned to withstand severe valvetrain loads. Once dialed in, the fastening mechanism ensures the gear remains locked in position, preventing timing slippage during aggressive high-RPM downshifts or when interacting with stiff aftermarket valve springs.
Technical Specifications
| Feature | UMA Adjustable Timing Gear Details |
| Adjustment Range | $\pm$5 Degrees |
| Material | CNC-Machined High-Grade Carbon Steel |
| Pin Configuration | 1-Pin Lobe Architecture |
| Engine Application | 155cc 4-Valve VVA LC Engines |
| Compatible Models | Yamaha R15 V3 / R15 V4 / R15M / MT-15 / NVX 155 / NMAX V2 |
| Special Function | Built-in Decompression Mechanism |
Why Use an Adjustable Timing Gear on the R15 Platform?
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Correcting Machining Tolerances: When a cylinder head is skimmed/milled, or when thick/thin racing cylinder head gaskets are used, the physical distance between the crankshaft and the camshaft changes slightly. This introduces unwanted timing deviations. The UMA adjustable gear allows a tuner to degree the camshaft back to true center.
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Maximizing Aftermarket Camshafts: High-lift racing camshafts (like the UMA R1, R3, or Stage 3 profiles) have specific power delivery traits. This gear allows you to fine-tune those profiles, ensuring the valves open exactly at the optimum degree of the piston stroke to achieve maximum volumetric efficiency.
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VVA Synchronization: Because the R15 features Variable Valve Actuation (switching to a high-lift cam lobe at 7,400 RPM), keeping physical valvetrain alignment absolutely flawless is essential to prevent valve-to-piston contact, especially when utilizing large 63mm big-bore pistons.
Tuner’s Installation Note
Adjusting cam timing changes the mechanical clearance between your valves and the piston crown. Dialing in too much advance or retard without measuring can cause the valves to strike the piston, leading to catastrophic engine failure. Always manually spin the engine over by hand and check for adequate valve-to-piston clearance before starting the bike after adjustment.
