EVO: Engine Control - Sub-01a

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====== EVO: Engine Control - Sub-01A ======
====== Finding TDC on Compression Stroke (1991-2003) ======
===== Using the Timing Mark on the Flywheel =====

The bike must be on a jack or a lift so you can spin the rear wheel. \\ It may be easier done with a helper to spin the wheel while you work the engine side although a one person operation can be done.

  * Remove both spark plugs (or one on each cylinder for an "S" model with 4 plugs). \\ This will relieve the compression on the engine as you turn the engine over.
  * Remove the timing plug (right side at the base between both cylinders).
  * **Use Caution while removing / installing this plug**. \\ It is a steel plug in an aluminum hole and it's common to either destroy the internal threads / sealing surface or to find them to be damaged upon removal. 
    * Once torque is removed (broken free) while backing it out, you should be able to turn it out by hand or by using just the Allen wrench socket gently by hand. \\ If you can't turn it out by hand, the threads could be warped or damaged from over torque the last time it was installed. \\ [[techtalk:ref:engmech01a|You can read more about it here]] including repair of damaged threads.
    * While installing the plug, set it in the hole and turn it backwards until you feel thread engagement before attempting to use any force to turn it into the hole. \\ You should be able to install it by hand as mentioned above to snug. Do not over-torque. \\ See also [[techtalk:ref:engmech01a#installing_the_plug|Installing the plug]].  

|  This can be removed with a 3/8" Allen hex wrench ((photos by Phillober of the XLFORUM http://xlforum.net/forums/showthread.php?t=1175659&highlight=tapping+threads&page=3))  ||
|{{:techtalk:evo:engctl:finding_tdc_compression_1_by_phillober.jpg?direct&300|}}|{{:techtalk:evo:engctl:finding_tdc_compression_2_by_phillober.jpg?direct&300|}}|

  * **Shift the transmission into 5th gear**.
    * With the rear wheel off the ground, shift into 1st gear. Then, rotate the rear wheel forward until it stops (this will turn over the engine / transmission). \\ You can also just turn the wheel over with one hand (a bump at a time) while shifting with the other. The wheel doesn't have to turn too far or at any rate of speed. 
    * Then you can shift thru 3rd.
    * It takes two separate movements of the shift forks to get into 4th which requires turning the wheel again. \\ Depending on the alignment of your specific transmission conditions, you may have to wing it back and forth with turning the wheel and shifting.
    * Then you can shift to 5th. Of all the gears to be in, 5th will be the easiest to turn by hand.

|  Shifting the transmission into fifth gear  ((photos by Phillober of the XLFORUM http://xlforum.net/forums/showthread.php?t=1175659&highlight=tapping+threads&page=3))  |||
|{{:techtalk:evo:engctl:finding_tdc_compression_3_by_phillober.jpg?direct&300|}}|{{:techtalk:evo:engctl:finding_tdc_compression_4_by_phillober.jpg?direct&300|}}| {{:techtalk:evo:engctl:finding_tdc_compression_5_by_phillober.jpg?direct&300|}}|

  * Slowly turn the rear tire forward to roll the engine over and you will see the TDC timing mark pass through the timing hole window. \\ It's faster with 2 people so one can watch the hole, but with one person, you can bump the wheel with one hand while watching the hole.
  * When the vertical line appears in the hole as below, you're piston is at TDC.
  * However, the piston is at TDC twice for each (one) revolution of the cams (once on TDC compression stroke and once on TDC exhaust stroke).


|  When you take out the timing plug, \\ this is more than likely what you see ((photo by Phillober of the XLFORUM http://xlforum.net/forums/showthread.php?t=1175659&highlight=tapping+threads&page=3))  |  TDC timing mark in center of window ((photo by Phillober of the XLFORUM http://xlforum.net/forums/showthread.php?t=1175659&highlight=tapping+threads&page=3))  |
|{{:techtalk:evo:engctl:finding_tdc_compression_6_by_phillober.jpg?direct&300|}}|{{:techtalk:evo:engctl:finding_tdc_compression_7_by_phillober.jpg?direct&300|}}|


  * **Using the "Finger Method" to find compression stroke (TDC compression)** \\ Basically, you just plug the hole with their finger and wait for pressure to blow past it. \\ There is a distinct difference you can feel between the 2 TDCs from your finger. \\ Here's what happens:
    * When at TDC (exhaust), both valves are open somewhat and the force of the piston pushing air is sent thru enough orifices that there will not be much pressure at at your finger although you may feel some air.
    * At TDC (compression) both valves are closed (leaving the plug hole as the main outlet for the air) which drastically increases what you feel at your finger. 

  * Bump the engine over until the TDC mark is in the window and back it off 1/4-1/2 turn. Then rotate the wheel forward with the mark going past the window with your finger over the spark plug hole. 
  * Once you start to feel pressure on your finger, your close. Press as hard as you want on the hole, the pressure will be stronger than you when your on compression stroke. You may need to roll the engine over several times until your sure of which TDC your at.

|  Using the "finger method" to feel compression ((photo by Phillober of the XLFORUM http://xlforum.net/forums/showthread.php?t=1175659&highlight=tapping+threads&page=3))  | 
|{{:techtalk:evo:engctl:finding_tdc_compression_8_by_phillober.jpg?direct&300|}}|

\\

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Trace: • IH: Engine Mechanicals - Sub-01E • REF: Engine Mechanicals • EVO: Electrical System • EVO: Specific Troubleshooting • EVO: Engine Control - Sub-01a
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