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techtalk:ref:tools169 [2019/09/11 05:39]
hippysmack [Timing Light]
techtalk:ref:tools169 [2019/12/05 05:12] (current)
hippysmack [Timing Light]
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 ====== REF: Tools - 169 ====== ====== REF: Tools - 169 ======
 ====== Timing Light ====== ====== Timing Light ======
 +A dialback timing light uses the TDC mark (the light delays the flash by the number of crankshaft degrees selected on the dial). ((aswracing of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1423947&​page=2)) \\
 +The dialback lights don't work well on dual fire Harleys, because they see twice as many sparks as there really are. \\
 +And therefore the light'​s calculation of rpm and how long to delay the flash are wrong. You have to select 56 degrees to get an actual delay of 28 degrees. \\
 +However, even setting the thing to double is no guarantee it's going to work right, because Harley engines don't fire evenly. \\
 +The firings occur at 315° and 405° intervals. So if the light sees two firings 315° apart, but assumes they'​re 360°. \\
 +It thinks the motor is running faster than it actually is. \\
 +And conversely, it may see a 405° interval, think it's 360 degrees, and assume the motor is running slower than it is. \\
 +The bottom line is that many dialback timing lights can't make sense of it, for the purposes of determining rpm, and you get a wrong answer. \\
 +Really the only reliable way to make it work on dual fires is to set the light'​s dial to 0 and look for the advance mark. \\
  
 |  Dialback timing light. ((photo by Ryan M of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1069628&​page=3)) ​ | |  Dialback timing light. ((photo by Ryan M of the XLFORUM http://​xlforum.net/​forums/​showthread.php?​t=1069628&​page=3)) ​ |