Determining top dead center

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m (Resources: Add Firing orders category.)
m (Removed Firing orders category, added Adjust valves category.)
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If using a camshaft with more duration, you may want to increase the ignition timing lead at the crank and limit the centrifugal advance in the distributor to achieve your total ignition timing. Some distributors, like those sold by MSD, use different bushings to control the ''amount'' of mechanical advance. The '''rate''' of mechanical advance is tailored by changing the springs and/or centrifugal weights. Usually just spring changes are all that is needed. If working on a GM HEI, the original weights are almost always a better choice than the weights sold in the various advance curve kits available from Mr. Gasket, Crane, Summit, Moroso, etc.  
 
If using a camshaft with more duration, you may want to increase the ignition timing lead at the crank and limit the centrifugal advance in the distributor to achieve your total ignition timing. Some distributors, like those sold by MSD, use different bushings to control the ''amount'' of mechanical advance. The '''rate''' of mechanical advance is tailored by changing the springs and/or centrifugal weights. Usually just spring changes are all that is needed. If working on a GM HEI, the original weights are almost always a better choice than the weights sold in the various advance curve kits available from Mr. Gasket, Crane, Summit, Moroso, etc.  
  
If you are using a radical cam and/or a converter that allows the engine to come up past where you would normally limit centrifugal advance (about 2800 rpm), you may want to alter the distributor so that centrifugal advance is locked out and put your total amount of ignition advance in at the crank. Of course, the engine will not want to crank against this much ignition lead, so you will want to install a momentary switch in the wire going to the "+" terminal of the coil to disable the coil while you crank the engine. Once the engine is spinning, release the switch and the engine will fire normally.  
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If you are using a radical cam and/or a converter that allows the engine RPM to come up past where you would normally limit centrifugal advance (about 2800 rpm), you may want to modify the distributor so that centrifugal advance is locked out and put your total amount of ignition advance in at the crank. Of course, the engine will not want to crank against this much ignition lead, so you will want to install a momentary switch in the wire going to the "+" terminal of the coil to disable the coil while you crank the engine. Once the engine is spinning, release the switch and the engine will fire normally.  
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File:HEI CAP- ELECTRODE- INSULATOR- COIL DIAGRAM.jpg
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File:HEI MAGNETIC PICK UP COIL V6 EVEN FIRE.jpg
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File:HEI COIL DATA RATIO WINDS ETC.jpg
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File:DIST THRUST BEARING-SPACER 003.jpg
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File:ROTOR where weights hit2.jpg
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File:HEIadvlimitlock2.jpg HEI adv. plate limiter
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File:Hei mechanical ADVANCEslots and pins 0011.jpg
  
There, you're done. You should feel much better now, knowing that when you set the ignition timing with a timing light, it's absolutely accurate.
 
  
 
==Resources==
 
==Resources==
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[[Category:Engine]]
 
[[Category:Engine]]
 
[[Category:Good articles]]
 
[[Category:Good articles]]
[[Category:Firing orders]]
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[[Category:Adjust valves]]

Revision as of 08:47, 21 March 2012

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