Using Rivnut kits to sample exhaust.

On some exhaust systems – like the Vance and Hines Power Duals, the best way to sample the exhaust at each cylinder is with a rivnut kit.

Looking at the popular kits

There are several companies that make rivnut exhaust sampling kits, including Dynojet and Screamin Eagle.

Tools: Both kits come with quality rivnut installation tools.

Rivnuts:

Screamin Eagle: We have had several issues with leaking from the Screamin Eagle hex-shaped rivnut. Please understand: When we say ‘leak,’ we’re referring to Oxygen (O2) leaking past the rivnut into the pipe. Every exhaust leak is also an O2 leak. The Air Fuel Ratio (AFR) gauges on the dynos we all use have Wide Band O2 (oxygen) sensors. Any oxygen that enters the pipe not from the combustion chamber will cause your AFR to read lean, and you to calibrate/tune the bike too rich.

I think most people don’t appreciate how sensitive this is. Most of the oxygen that enters the combustion chamber is burned during combustion. The amount of O2 in the pipe that we measure with our O2 sensors to calculate the Air Fuel Ratio (AFR) is minimal. What seems like a small leak can make a very big difference in your readings.  Every week, we get dyno run files through our tech form that have O2 data which is corrupted from a leak.

A hex-shaped nut just doesn’t seal correctly in a round hole.   We HIGHLY recommend you do not use them. Instead use knurled round rivnuts. We have sourced replacement rivnuts on Amazon. They’re eligible for Prime shipping, so they’ll get to you in two days (if you’re a Prime member). These rivnuts work with the Screamin Eagle tool – and the fitting that attaches the metal sample tube to it.

Dynojet: The rivnuts with the Dynojet kit are knurled, round rivenuts and when installed correctly do not leak. They are metric so they will not work with the Screamin Eagle kit.

Installation tips:

  • Pick a spot under the heat shield on the outside of the pipe that you can drill easily with the drill perpendicular to the pipe.
    • Make sure the spot does not interfere with the heat shield straps, O2 sensors, bungs, etc.
    • Closer to the exhaust port reduces chances of reversion contamination like cross talk or leaks at pipe connections.
  • To help get a round hole for a good seal hold the drill perpendicular to the pipe and steady.
    • Drill the hole slowly
    • With a small bit.
    • Then open it up with an in-between bit.
    • Drill final size.
  • Read the instruction for the installation tool you have.
    • Use the rivnut tool according to the instructions.
    • Hold it perpendicular to the pipe and tight against it when squeezing/setting the rivnut, following the tool’s instructions.

 

Sample tubes:

Dynojet uses a banjo-type system, which attaches the sample tubes at parallel to the exhaust pipe with copper sealing washers.

Screamin Eagle uses an adapter that attaches the sample tube perpendicular to the exhaust pipe with a flare fitting.

Tips:

  • Use High Temperature Nickel Anti-Seize on the threads of the Screamin Eagle fitting or Dynojet Bolt.
    • Only on the threads, not in the holes or tubes.
  • To help keep the high temp neoprene hose from melting and losing its seal, the metal sample tube needs to be a certain length. Do not cut them shorter.
    • It is ok to put slight bends in the tubes.
  • Route the tubes so they will not rub on anything, including your leg.
  • It is common for the tubes to loosen with heat cycles. Check them regularly throughout the dyno runs, and keep an eye for the gauge to start showing leaner indicating a leak.

Plug Bolts:

Dynojet uses a button head bolt with a copper washer.

Screamin Eagle uses a hex bolt.

Both fit under the heat shields and work fine if you never have to remove them.

Tip: While there are no guarantees, you can greatly increase your odds of removing the blot/plug and using the rivnut again by using a Brass Hex Head Bolt (¼ 20 for Screamin Eagle) with High Temperature Nickel Anti-Seize.

Have any tips to add? Give us a shout. We love to learn new things and share what we learn.

Keep an eye on our Dyno Tool Store as we are always adding to it and updating it.

 

 

 

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