These early engines had Oo overlap or no overlap whatsoever. The burnt gases, due to their high pressure, virtually expel themselves, and the piston drives the last of the gases out the exhaust valve closes at T.D.C. The spark plug fires and ignites the fuel/air mixture which drives the piston down to B.D.C. The piston rises, with both valves closed to compress the fuel/air mixture. The old valve timing then was: Intake valve opens at T.D.C., and as the piston lowers, it draws in the fuel/air mixture the intake valve then closes at (B.D.C.) hence, the intake stroke. Even in their wildest inspirations they would never have believed that a quarter or half century later, with better structures, these same engines would be revved five times as fast and produce many times more power. They were merely concerned with getting the engines to run at slow speeds. The engineers of the late 1800's were only concerned with harnessing power of the gasoline and air explosions in an internal combustion engine to propel an automobile, hopefully, a little faster than a horse. In the old days, the first four cycle engine had very short valve timing, but rightfully so because these were slow speed engines.
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Its purpose is to operate the intake and exhaust valves in the correct timing with the piston as it sequences thru the four strokes. The camshaft is connected via the timing chain and sprockets at a 1:2 ratio to the crankshaft and therefore revolves once for every two turns of the crank. Two revolutions complete one sequence of the four strokes. 4 cycles x 180° = 720° or two revolutions of the crankshaft.
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Each stroke represents one-half of a revolution of the crankshaft or 180 crank degrees. You probably already know the four basic strokes of the four cycle engine: INTAKE, COMPRESSION, POWER, and EXHAUST. I would love for someone using autotap to confirm this for me,I'm going to mess with my efilive and see if I can't get it to do something so maybe I can use that instead.Ĭustomer comes back tomorrow,and if EFIlive won't work again I plan to set the CMP to 4087 on autotap,CASE relearn and verify.Indeed, cam degreeing is simple, but first let's make sure you have a good understanding of the cam's function in the four cycle engine. Sweet spot seems to be between 407x and 408x degrees for CMP,with the cherry being about 4087/88. Now,the reason for this post is I found the following information on a dated thread on (autotap site).Īpparently there is an issue in the autotap program and CMP retard reads incorrectly.
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I'm starting to figure the distributor is one tooth off (customer swapped it,said it dropped right in.) Turning the distributor as far clockwise as possible made the truck run like crap,but brought the CMP retard down to about 40*. and 1345 code),couldn't get efilive to work so plugged in autotap.Īutotap was reading the CMP retard at 4,08x degrees. Plugged in with EFIlive to reset the crank (new dist. Had a customer come in with an issue nobody can figure out,and i'm pretty sure it's the CMP retard (among other things).