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Tillotson 240RX 4-Cycle Racing Engine Bottom End Kit
Complete Exploded View of the EC 240RX Short Block
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Tillotson 240RX 4-Cycle Racing Engine Bottom End Kit

Part Number: 240RX-KIT
1 Review(s)
Online Price: $509.99
Tillotson 240RX Racing Engine Bottom End Kit – High-Performance 4-Cycle Kart Build
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Description

Tillotson 240RX 4-Cycle Racing Engine Bottom End Kit


Build your own high-performance kart or minibike engine with the EC 240RX Racing Engine Bottom End Kit—a purpose-built foundation for serious racers seeking maximum displacement and power. Designed around our latest lightweight forged piston and a 59mm stroker crankshaft, this kit is engineered to deliver top-tier performance where displacement rules don’t apply.


Why Choose the 240RX?

There’s no replacement for displacement—and this kit proves it. Compared to the 236cc open-class build, the 240RX adds even more volume and compression using a 59mm crankshaft rather than a 58mm. The result? Increased displacement, torque, and top-end power.


Key Components & Specifications:

EC 72mm Lightweight Forged Flat-Top Piston

  • Weight: Just 122g (vs. Tillotson hypereutectic piston at 131g)
  • Construction: Forged for strength, with moly-coated skirts for reduced friction and extended life
  • Compression Height: Reduced to allow use of a longer rod
  • Available Oversizes:
    • 72.00mm (240.22cc / 14.66ci)
    • 72.10mm (240.89cc / 14.70ci)
    • 72.25mm (241.89cc / 14.76ci)
    • 72.50mm (243.57cc / 14.86ci)
    • 72.75mm (245.24cc / 14.97ci)

EC Forged 3.54” Billet Aluminum Connecting Rod

  • Made from 7075 forged aluminum for superior strength and durability
  • Designed to achieve zero deck height with the EC 72mm piston
  • Anodized for oxidation resistance and reduced scuffing

Tillotson 72mm Reinforced Block

  • Originally developed for Tillotson’s 225RS/T4 class endurance engines
  • Reinforced design resists flex, blow-by, and distortion under high power
  • One of the largest bore blocks available factory-direct

EC 59mm Stroker Crankshaft

  • Adds 1mm stroke over standard 58mm cranks
  • Pre-clearanced for most camshafts (EC Exclusive)
  • Uses 1.180” Honda/Clone crankpin for added durability vs. .998” pins


What’s Included:

  • 72mm Tillotson Reinforced Block
  • EC 72mm Forged Flat Top Piston (standard size, unless specified)
  • EC Forged 3.54” Connecting Rod
  • 59mm Stroker Crankshaft (pre-clearanced)
  • Stock Side Cover
  • Complete hardware and gasket kit for short block assembly

Note: Pushrods not included. Chromoly recommended for high-output builds.


Optional Upgrades:

  • Billet Side Cover – Improves block rigidity and crank stability for extreme builds
  • Color-matched Blower Housings & Recoils – Add style and a kill switch
  • Cylinder Heads, Cams & Carbs – Pair with our ported heads and custom cams for peak power


Builder’s Note:

This is a high-performance racing kit. Final assembly, tuning, and compatibility checks (such as piston deck height and cam clearance) are the builder’s responsibility. We do not offer warranty on racing engine packages.

For assistance with part matching or combinations, feel free to contact us directly via phone, email, or the Q&A tab on this page.

FAQ

Frequently Asked Questions – Tillotson 240RX Bottom End Kit


Does the 240RX kit require any machining or clearancing?

The components included in the 240RX bottom end kit are designed for drop-in installation and do not require any additional machining or clearancing for assembly under most conditions.
However:

  • Some camshafts may need minor clearancing for compression releases or aggressive lobes, especially with larger duration profiles.
  • If you are using a copper head gasket, we recommend having the cylinder head o-ringed to ensure proper sealing under higher compression ratios.


Do you assemble the 240RX engine?

No, we do not pre-assemble the 240RX engine kit.
This kit is designed for experienced engine builders who may need to:

  • Choose a specific camshaft, flywheel, or cylinder head based on their performance goals.
  • Make adjustments or clearancing that vary from build to build.

Pre-assembly would require disassembly for tuning and modifications anyway, so selling the kit unassembled gives you more flexibility and keeps costs lower.


Can I use this kit with other blocks or crankshafts?

This kit is specifically designed for the Tillotson 72mm reinforced block and 59mm crankshaft. While the parts may physically fit other blocks or cranks, we do not support or guarantee compatibility with non-Tillotson or non-EC engine combinations.
For a full short block, we recommend the 240RX U-Build-It Kit for best results.


How much horsepower can the 240RX kit make?

Horsepower varies significantly based on tuning, carburetion, camshaft, exhaust, and headwork. While we do not claim an official power rating due to lack of SAE-certified dyno testing, here are general guidelines for context:

  • Classic factory hot rods (~1960s–70s) made around 1 HP per cubic inch. At 14.7ci, that’s around 14.7 HP — already a high-performance number for this engine class.
  • Pro Stock engines of that era hit 2 HP per cubic inch. At 14.7ci, that's 29.4 HP — an extremely aggressive and highly optimized build.
  • Modern Pro Stock engines push 2.5–3 HP per cubic inch, which would theoretically be 36–44 HP at 14.7ci. This is not achievable in a power equipment-based, air-cooled 4-cycle engine due to practical and thermal limitations.

In short, 14–20 HP is realistic with proper tuning and component matching. Anything higher requires professional-level development, exotic fuels, and parts reliability trade-offs.


What else do I need to complete the 240RX engine?

The 240RX Bottom End Kit includes:

  • Block, crank, piston, rod, sidecover, and assembly hardware.

To complete your build, you’ll need:

  • Cylinder head
  • Camshaft
  • Flywheel
  • Ignition system
  • Carburetor and intake
  • Header/exhaust
  • Pushrods (chromoly recommended)
  • Blower housing (optional aesthetic and cooling upgrade)

We offer compatible parts and U-Build-It kits to match your performance goals and budget.

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Customer Reviews

Tillotson 240cc
The tillotson 240cc with the forged racing piston is the smoothest running engine I have built yet. Very little vibration. Using this kit and a stroker Dyno Cam there will be no clearancing. required. I would recommend this engine kit and it is one of my favorite.
Did you find this helpful?  11 of 11 Found Helpful
Reviewed by:  from Fort Atkinson on 12/19/2024
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