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Tillotson 225R/RS 27/25 5mm Cylinder Head Assembly w/26lbs Springs
138220050 Tillotson 225RS Cylinder Head Assembly w/26lbs Springs
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Tillotson 225R/RS 27/25 5mm Cylinder Head Assembly w/26lbs Springs

Part Number: 138220050
1 Review(s)
Online Price: $89.99
Tillotson 225RS Cylinder Head – JT-207 | 5mm Stem, 27/25mm Valves, GX200 Clone Upgrade
Availability: Out of Stock.

Description

Tillotson 225RS Stock Cylinder Head – JT-207 Performance Assembly for GX200/Clone Engines


The Tillotson 225RS Cylinder Head (JT-207) is a high-performance, factory-configured head engineered specifically for the Tillotson 225RS and 212R racing engines. Originally developed for the 196R Box Stock engine, this head has evolved into a versatile and powerful upgrade for multiple small engine platforms, including Honda GX200, Predator 212, Wildcat, and Ducar clone engines.


Designed with 5mm valve guides, 27mm intake, and 25mm exhaust valves, the 225RS version also features 26 lb valve springs, making it a reliable bolt-on option for many mild and mid-range camshaft profiles, such as the popular MOD2and Banzai 265 cams.


Key Features:

  • Intake Valve: 27mm
  • Exhaust Valve: 25mm
  • Valve Stem Size: 5mm (reduced weight & friction)
  • Combustion Chamber: ~20.9cc
  • Includes: Rocker arm assembly, retainers & locks, pushrod guide, 26 lb valve springs
  • Split-lock retainers for enhanced valve retention
  • Compatible with mild/moderate cams like MOD2 and .265 lift profiles


Fitment & Compatibility:

  • Direct fit for Tillotson 225RS and 212R engines
  • Originally designed for Tillotson 196R with 5.5mm guides (updated to 5mm in 212R/225RS versions)
  • Fits most Honda GX200, Clone, and Ducar small blocks
  • Compatible with Predator 212 Non-Hemi, but requires modification for 12mm dowels
  • Hemi-head engine conversions may need different pushrod lengths


Technical Insight:

The use of 5mm valve stems not only reduces friction and weight, but also improves airflow for better engine response. This is the first-generation 225RS cylinder head and can be decked ~.040" to meet T4 and T225RS competition rules, allowing combustion chamber depth to comply with the minimum spec: 5.5mm (0.216”) ± 0.3mm (0.0118”).


Racing Tip:

For racers competing in the Tillotson T4 or T225RS class, it's wise to keep spare heads on hand. Much like the Briggs LO206, the valve seal is critical for maintaining spec power levels. Due to high exhaust temps created by the rev-limited coil and spec mufflers, the exhaust valve and seat can wear over time—resulting in power loss due to combustion leakage.

FAQ

Q1: What engines is this cylinder head compatible with?
A: This head fits Tillotson 225RS, 212R, 196R (with original valve sizes), and many GX200-style clone engines such as Predator 212 (non-hemi), Wildcat, and Ducar. Modifications may be required for 12mm dowel fitment or pushrod length.


Q2: What makes this head different from the 212R version?
A: The 225RS version comes equipped with 26 lb valve springs, which support more aggressive cams like the MOD2 and .265 lift profiles, making it ideal for performance applications.


Q3: What are the benefits of 5mm valve stems?
A: They reduce overall valve weight and friction, helping improve airflow and valve response for better engine performance.


Q4: Can I use this with a Predator 212 non-hemi engine?
A: Yes, but you must modify the head to accommodate the Predator's 12mm dowel pins (this head uses 10mm). Additionally, non-hemi to hemi conversions may require pushrod length adjustments.


Q5: Is this head compliant for Tillotson T4 or T225RS class racing?
A: Yes, but this is the Gen 1 head and may need to be decked ~.040" to meet the minimum combustion chamber depth (5.5mm ± 0.3mm) to be optimized for competition. 


Q6: Why should I keep a spare cylinder head for T4/T225RS racing?
A: Due to high temps from rev-limiters and spec exhausts, the exhaust valve and seat wear over time, leading to valve leakage and power loss. Having a spare ensures consistent performance during racing.

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Customer Reviews

JT-207 head is awesome
Awesome head for the money it performs so much better than a stock predator one. You can touch up the ports a little and gain a lot. It came on my Tillotson 212r, I put a billet rod, .010 head gasket not sure what compression is now, Nibbi pe24mm carb and a dyno cam super X .265 cam 232 duration and 26lbs springs, wanted a motor to hopefully be a beater but perform and last so far 3 tanks of WOT around my buddy's dirt oval running 12 62 gearing so far no problems other than clutch dragging a little. But the head Makes Amazing power out of the hole, great torque and still will pull 9k. The intake I have if I'm riding long enough will almost form ice on it the head is flowing so much.
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Reviewed by:  from CT on 6/24/2023
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