Sunday, March 31, 2013

Tips on installing a new Alternator on the Miata

Creating this short article to try and help out others who may be confused trying to setup the tensioner bolts. I've seen a few people in the pits struggling with them and a few people DNF when they installed them incorrectly.

When I was unloading the Miata after the last race, I noticed that the headlights seemed dim.  So I located my voltage tester and started the car to check the voltage.  Sure enough, voltage was around 12 volts measured at the battery terminals with the car running.  Should be about 14 volts when running.  So I went over the local O'Rielly's Auto Parts and got a new alternator.  Shiny. :)

Here is a pic of the tensioner bolts:

Here is a pic of the tensioner bolts positioned on the alternator off the car:

Here is a pic of the tensioner bolts positioned on the alternator bracket on the car:

Here I have positioned the alternator on the tensioner bracket and fed the bolt through the alternator.  Don't tighten the bolt that goes through the alternator too much yet as you still need to tension the belt properly.

In order to properly tension the belt, don't try to wedge a screw driver or something to put tension on the belt.  Instead, tighten the long bolt against the bracket using a 12mm ratcheting socket.  Don't overtighten.  The only purpose of the long bolt is to put tension on the belt.  Once you have the belt tight, tighten the short bolt that goes through the tensioner block and attaches the alternator to the tensioner bracket.  Don't overtighten this bolt either as it threads into the soft aluminum of the alternator.  Hopefully the following pic does a good job of explaining this visually:

Hope that helps.  Check to ensure that it remains tight next time you run or drive the car just in case....
Also make sure you install the air tube/intake correctly so it doesn't rub up against the alternator belt.


  1. Do you know where I can find those bolts. I have mine rigged at the moment but am looking for a more permanent solution. Upon doing some research I realized that I don't have the tensioner bolts.
    Thanks - Troy

  2. Hi. Try Blake at

    Email him for those. He probably doesn't list them.