TRIUMPH 70-6851 Tappet Blocks 68. 70-4676 70-5861

( Manufacturer Part Number: 70-6851 ), ( Part Type: Tappet Block Guide ), ( Country Of Origin: United Kingdom )

Review TRIUMPH Tappet Guide Blocks 68. fits BONNEVILLE TROPHY 650 1966

The Triumph Bonneville Trophy engine components, specifically the **Triumph 70-6851 650cc tappet blocks** (compatible with models 1966 through 1970, including the 70-4676 and 70-5861 variants), represent a meticulously crafted set of aftermarket parts designed to restore or enhance the performance and longevity of one of the most iconic British twin-cylinder engines ever produced. These tappet blocks are engineered to fit seamlessly into the classic Bonneville s overhead valve (OHV) cylinder head, where they serve as the critical interface between the camshaft lobes and the pushrods, ensuring precise valve actuation. Crafted from high-quality, heat-treated steel, these blocks are precision-machined to exacting specifications, guaranteeing a snug yet smooth fit within the cylinder head s bore, which minimizes wear and prevents premature failure a common issue in older engines subjected to high mileage or aggressive riding styles. The design incorporates a robust, slightly tapered profile that not only reduces friction but also allows for easy installation, even for those working on their first restoration project. Beyond their functional integrity, these tappet blocks are a nod to Triumph s engineering heritage, embodying the same attention to detail that defined the Bonneville s legendary reliability and timeless appeal. Whether restoring a showroom-fresh Trophy or reviving a well-loved classic, these components are an essential upgrade for riders seeking to preserve the soul of their machine while modernizing its mechanical robustness. Pairing these with genuine Triumph valves, springs, and retainers completes the package, offering a full rebuild solution that breathes new life into the engine s performance, ensuring smooth operation, improved throttle response, and the satisfying growl of a properly tuned twin. For enthusiasts who value authenticity and craftsmanship, these tappet blocks are a testament to the enduring legacy of the Bonneville, bridging the gap between vintage charm and contemporary reliability.

### **Pros and Cons of Buying Triumph Tappet Blocks (Models 70-6851, 650, 1966-70, 4676, 5861, Bonneville/Trophy)**

#### **Pros**

1. **Compatibility and Fitment** These tappet blocks are designed specifically for Triumph Bonneville and Trophy models from the late 1960s and early 1970s, ensuring a precise fit without modification. They are widely used in restorations and rebuilds of these engines, particularly the 650cc models (T69, T69B, T69D, etc.).

2. **Quality Materials** Triumph s original tappet blocks were made from durable cast iron, which provides good wear resistance and longevity. Aftermarket versions (such as those from **Bonneville Specialties, Triumph Parts, or eBay sellers**) often replicate this quality, ensuring reliability in high-mileage or modified engines.

3. **Ease of Installation** Since these blocks are designed for stock Triumph engines, they integrate seamlessly with existing components like the crankshaft, camshaft, and cylinder head. No major machining is typically required unless the engine has been heavily modified.

4. **Cost-Effective Replacement** Compared to rebuilding an entire engine, purchasing a used or refurbished tappet block can be significantly cheaper. Prices vary, but a set can often be found for **$50 $200**, depending on condition and seller.

5. **Performance Potential** When paired with upgraded cams, pistons, or other performance parts, these blocks can support higher RPMs and torque. Many Bonneville/Trophy owners use them in **street, cruiser, or even light racing applications** with success.

6. **Availability of Parts** Due to the popularity of Triumph motorcycles, replacement parts (including tappet blocks, bearings, and seals) are still widely available through specialty shops, online marketplaces, and Triumph s official parts catalog.

7. **Restoration Value** For classic motorcycle enthusiasts, using original or high-quality aftermarket tappet blocks helps maintain the engine s authenticity, increasing the bike s resale or show value.

---

#### **Cons**

1. **Age and Wear** Original Triumph tappet blocks from the 1960s 70s may show signs of wear, corrosion, or cracking over time. If purchasing used, inspection for **cracks, rust, or uneven wear** is essential to avoid premature failure.

2. **Limited Modern Upgrades** Unlike newer engines, these blocks are not designed for extreme performance modifications (e.g., big bore kits, aggressive cams, or forced induction). Overstressing them can lead to **premature wear or catastrophic failure**.

3. **Potential for Incompatibility** Some aftermarket blocks may not fit perfectly if the engine has been heavily modified (e.g., custom crankshafts, oversized rods, or non-standard cylinder heads). Always verify fitment before purchase.

4. **Reliability Concerns with Cheap Aftermarket Blocks** While some aftermarket blocks are well-made, others may be poorly cast or finished, leading to **premature wear or oil leaks**. Buying from reputable sellers (e.g., **Bonneville Specialties, Triumph Parts, or trusted eBay sellers**) reduces this risk.

5. **Maintenance Requirements** These engines benefit from **regular oil changes, valve adjustments, and timing checks**. Neglecting maintenance can lead to **tappet wear, camshaft damage, or bearing failure**, even with a new block.

6. **Limited Warranty Options** Most aftermarket blocks come with **no warranty**, so if issues arise, the buyer is responsible for repairs. Original Triumph parts may have limited warranty coverage.

7. **Skill Level Required** Rebuilding or installing a tappet block requires **mechanical skill**, especially if dealing with older engines prone to **rust, seized components, or alignment issues**. Beginners may need professional help.

---

### **Conclusion**

The Triumph tappet blocks (70-6851, 650, 1966 70, 4676, 5861, Bonneville/Trophy) are a **practical and cost-effective solution** for restoring or maintaining these classic engines. They offer **good compatibility, durability, and performance potential** when used correctly. However, they come with **potential drawbacks**, particularly regarding **wear, compatibility with modifications, and maintenance demands**.

For **restoration projects or stock/lightly modified engines**, these blocks are an excellent choice. For **high-performance or heavily modified setups**, they may require additional reinforcement (e.g., upgraded bearings, cams, or even a custom block).

---

### **Recommendation**

- **If restoring a classic Bonneville/Trophy:** Purchase a **new or refurbished set from a reputable supplier** (e.g., **Bonneville Specialties, Triumph Parts, or a trusted eBay seller**). Inspect for **cracks, rust, and wear** before installation.

- **If modifying the engine:** Ensure compatibility with **crankshaft, rods, and camshaft**. Consider **upgraded bearings and seals** to prevent premature failure.

- **If unsure about installation:** Consult a **Triumph specialist or motorcycle mechanic** experienced with these engines.

- **For budget buyers:** A **used but well-maintained set** can be a good deal, but **avoid blocks with visible damage**.

- **For performance builds:** Consider **aftermarket blocks with reinforced designs** (e.g., **Bonneville Specialties high-performance options**) if pushing the engine beyond stock limits.

**Final Verdict:** These tappet blocks are a **solid choice for classic Triumph owners** who prioritize **authenticity, reliability, and cost efficiency**. With proper care and maintenance, they can provide **decades of service** in a Bonneville or Trophy engine.

Details:

Pair of tappet blocks for 1966-'68 Triumph T120 Tr6 twins. Intake block can also be used for 500 twins. Good used condition, see pics.

part #: 706851 prices

• $30.68-$61.75

specifications cartrimmouldings:

• for models: 650, Bonneville, Trophy
• for makes: Triumph
• for years: 1966
• mpn: 70-6851
• part type: Tappet Block Guide
• country of origin: United Kingdom

payments cartrimmouldings:

• credit card: Diners-club
• wallet: Paypal
• other

offer cartrimmouldings:

• quantity: 1
• availability: In Stock
• options: Ship-to-home
• sold: 0
• best offers: True
• started: April 25, 2026

seller cartrimmouldings:

• rating: 100.0%
• city: Madison, Wisconsin
• # reviews: 805

returns cartrimmouldings:

• policy: Returns Accepted
• paid by: Buyer
• time: 30 Days

shipping cartrimmouldings:

• carrier: USPS
• transit: 4-9 Days
• cost: $7.31
• class: Standard
• type: Calculated
• service: USPS Ground Advantage

general cartrimmouldings:

• Car Truck Parts Accessories > Exterior Parts Accessories > Body Moldings Trims
• condition: Used

Triumph 70-6851 Is Similar To:

• Triumph 83-4606 1973 Ft78 T140 Bonneville Air Box (43% similar) Plastic covers are still usable, but not pristine. These are for bonneville and not tiger. These came from a 750, but could be used on 1971 1972 650S. Only difference is the thread bosses where side covers attach are flush. Air box and plastic filter covers from 1973 - 1978 triumph 750 T140 ...(June 15th, 2025)