Choosing the Right Spark Plugs for a 2010-2011 Big Dog Mastiff EFI
Keep your S&S V-twin running strong by understanding which spark plugs work and which can cause issues.
- The 2010-2011 Mastiff EFI requires resistor-type spark plugs to prevent electronic interference with the ECU.
- The recommended OEM plug is the Champion RA8HC for the S&S 117ci engine.
- NGK plugs, such as the DCPR7E, are a popular and reliable aftermarket alternative used by many owners.
- Always check and set the spark plug gap to between .038 and .042 inches before installation.
Symptoms of Failing Spark Plugs
Worn or faulty spark plugs can cause a range of problems on your Mastiff. If you notice any of these signs, it might be time for a new set.
- Hard Starting: The engine turns over but struggles to fire up, or won't start at all. This can happen if the plug gap is too wide from wear or if the plug is fouled.
- Rough Idling: The bike may vibrate excessively or sound uneven at a standstill.
- Misfiring or Stumbling: During acceleration, you might feel the engine hesitate or stumble. This is often a sign of a weak or inconsistent spark.
- Reduced Fuel Economy: Inefficient combustion from bad plugs means the engine uses more fuel to produce the same amount of power.
- Engine Fouling: Using the choke (enrichener) too much can quickly foul the plugs with fuel, causing it to run poorly. A visual inspection showing a black, sooty, or wet plug indicates a problem.
Radio Frequency Interference (RFI) is a Real Concern
The 2010-2011 Mastiff EFI relies on an electronic control unit (ECU) for ignition and fuel management. Using non-resistor spark plugs can create significant RFI, which may cause drivability issues, loss of performance, or even cause the ignition module to shut down. Big Dog originally equipped these bikes with Champion resistor plugs for this reason.
Choosing the Right Aftermarket Spark Plug
When shopping for new spark plugs for your Mastiff's S&S 117ci engine, brand choice and plug type are important. While Big Dog originally specified Champion plugs, many owners have successfully used other brands like NGK, as long as they are the correct resistor type.
Brand Tiers
- Tier 1 (OEM Recommended): Champion
S&S and Big Dog Motorcycles recommend Champion resistor plugs. The Champion RA8HC is the specified plug for the 117ci engine found in 2005-2011 models. These plugs are designed to suppress the RFI that can interfere with your bike's electronics. They are a reliable, cost-effective choice that meets the engine's original requirements. - Tier 2 (Popular Aftermarket): NGK
NGK is a very popular alternative among Big Dog owners. Many riders report good performance and reliability with NGK plugs, sometimes preferring them over Champion. The NGK DCPR7E and its iridium equivalent, the DCPR7EIX, are common choices for the 117ci S&S engine. While not the OEM brand, they are a high-quality option.
Pro Tip: Regardless of brand, always check the spark plug gap before installation. For the S&S 117 engine, the recommended gap is typically between .038 and .042 inches. Applying a small amount of anti-seize compound to the threads can make future removal easier, though some plug manufacturers state it's not needed with modern coatings.
New Aftermarket Spark Plug Cost (2010-2011 Big Dog Mastiff EFI)
| Part | Brand | Price Range (per plug) |
|---|---|---|
| Spark Plug (Copper) | Champion RA8HC | $3.91 - $6.00 |
| Spark Plug (Copper) | NGK DCPR7E | $4.00 - $7.00 |
| Spark Plug (Iridium) | NGK DCPR7EIX | $10.00 - $14.32 |
Note: Prices are estimates and may vary based on the retailer and availability. Your motorcycle requires two spark plugs.
Frequently Asked Questions
Do I have to use Champion spark plugs?
No, but it is highly recommended to use a resistor-type plug to avoid electronic interference. While Champion was the original equipment, many owners use NGK resistor plugs like the DCPR7E with no issues.
What is the correct spark plug for my 2011 Mastiff EFI?
The 2010-2011 Mastiff with the S&S 117ci engine uses a 12mm spark plug. The recommended Champion part number is RA8HC. A common NGK alternative is the DCPR7E.
How often should I change my spark plugs?
S&S recommends inspecting the spark plugs every 5,000 miles and replacing them every 10,000 miles, or as needed. Many owners choose to replace them more frequently, such as every year or with every oil change, since they are inexpensive.
Are there any recalls or TSBs for my bike's spark plugs?
There was a service bulletin (SB1097) issued on October 12, 2007, for all 2007 and 2008 EFI models that required a spark plug wire replacement. While this does not directly involve the 2010-2011 models, it highlights the sensitivity of the ignition system. No specific recalls for spark plugs were found for the 2010-2011 Mastiff EFI.
Technical Specifications
OEM Part Numbers: RA8HC
Engine: S&S 117ci V-Twin Spark Plug Type: 12mm Resistor Type Recommended Gap: .038" - .042" Torque Spec: 11-18 ft-lbs
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
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