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IGNITION TIMING

IGNITION TIMING. AUTO 2. Ignition Timing. Timing wasn’t adjustable on your Briggs & Stratton's Engines were designed to run at a steady governed speed so timing was set at factory to work best at that speed

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IGNITION TIMING

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  1. IGNITION TIMING AUTO 2 VHS AUTO

  2. Ignition Timing • Timing wasn’t adjustable on your Briggs & Stratton's • Engines were designed to run at a steady governed speed so timing was set at factory to work best at that speed • An Automobile needs good power and fuel efficiency at all driving speeds so timing needs to be changed to meet all these demands VHS AUTO

  3. But it will take some Time to burn! Ignition Timing • Time it takes to burn an A/F mixture depends on: • Compression ratio • Mixture (ratio & mixed up) • Combustion chamber shape and size • Placement of spark plug in chamber • Throttle opening & RPM • Other small factors VHS AUTO

  4. Ignition Timing • Engineers generally agree that we need the biggest push down on the average piston around 23o ATDC VHS AUTO

  5. Overadvanced Timing (too soon) • Causes • Detonation • Second explosion of A/F after plug lights • Hard cranking (balking) • More of one type of emission VHS AUTO

  6. Retarded Timing (too late) • Causes • Low Power • Less efficiency (mpg) • More emissions • Backfiring out the throttle plate • Lower engine vacuum (manifold) • Higher cylinder temperature • Hotter running engine VHS AUTO

  7. Look at this picture In your notebook (top left picture) Ignition Timing Lets say this engine is running at 1650 RPM (write it down by the picture) 23o Lets say this engine takes 4 mS to burn the A/F to get good pressure and we want the big push at 23o ATDC VHS AUTO

  8. Ignition Timing • At 1650 RPM, how far is the crankshaft going to move during 4 mS (.004 seconds)? Think think think thinkkkkkk, how am I going to do this? • Lets get RPM to RPS • 1650 divided by 60 = 27.5 RPS • There are 360o in a circle so • 360 times 27.5 = about 10,000o per second of crank • There are 1000 mS per second so • 10,000 divided by 1000 = 10o per mS • 10o per mS times 4 mS = 40o I got it, At 1650 RPM the crank will move about 40o in 4 mS VHS AUTO

  9. Write in 23o ATDC Write in answer here Ignition Timing 40o Calculate how many degrees before TDC the spark will need start to get the big push at 23o ATDC VHS AUTO

  10. Ignition Timing • Now take the same engine and rev it up to 2500 RPM and say it still takes 4 mS to get the good burn and push on the piston. • If we leave the starting point at 17o BTDC the BIG PUSH will happen too late • Lets calculate VHS AUTO

  11. TOO LATE 17o BTDC 43o ATDC 2,500 RPM Ignition Timing 2500 divided by 60 = 41.66 RPS 41.66 times 360 = 15,000 degrees per second 15,000 divided by 1000 = 15 degrees per mS 15 times 4 mS = 60 degrees Calculate when the big push will Happen and fill in on drawing VHS AUTO

  12. Ignition Timing • So what we need to do is to advance the starting point when we rev up the engine • Copy the numbers from your top engine over to the top engine on the next page in your notebook VHS AUTO

  13. 23o ATDC Ignition Timing 17o BTDC 40o At 1650 RPM VHS AUTO

  14. Ignition Timing If we are going to maintain the big push at 23o ATDC at 2500 RPM, Calculate where we are going to have to advance the timing too? 23o VHS AUTO

  15. Ignition Timing • So when we speed the engine up, we will need to have the spark take place sooner • We are not going to change the dwell • Specifications needed to maintain proper saturation time and point opening • So how are we going to change the timing according to engine load and speed? VHS AUTO

  16. Vacuum Advance Vacuum advance rotates points on breaker plate around The distributor cam to advance when the points open and close VHS AUTO

  17. VACUUM APPLIED VHS AUTO

  18. 1 2 3 Vacuum Sources Find page in notebook 600-800 RPM 1200-1500 RPM O-1” #1 Venturi 15-20” #2 Ported 16-21” 15-20” 1400-2200 RPM #3 Manifold 3-5” 1-3” Venturi not strong Enough to use for Vacuum advance 13-20” 0-2” 13-20” 0-2” 0” 0” VHS AUTO 19-26”

  19. Vacuum Advance Notes • Vacuum comes from either: • Manifold • Ported • Dwell variation is the amount the dwell changes as the vacuum advance arks around the distributor cam or as the distributor cam wobbles in it’s bushing. • Maximum acceptable variation is 3o of dwell VHS AUTO

  20. Mechanical Advance Mechanical (centrifugal) advance advances the distributor cam to the distributor shaft to open points sooner VHS AUTO

  21. Mechanical Advance Notes • Weights over-come springs to turn the distributor cam as engine speed increases • As engine speed decreases, springs pull back weights and retard distributor cam back to where we started • Advance affected by: • RPM • Spring tension • Weight of weights VHS AUTO

  22. Manual Scale Meter VHS AUTO

  23. MILLIONS SIX WHOLE NUMBER THOUSAND THREE WHOLE NUMBER THOUSANDTHS (mili) THREE DECIMAL MILLIONTHS (micro) SIX DECIMAL VHS AUTO

  24. No “M”, “K”, or “m” .251 amps 674 ohms 6,740 ohms 6,740,000 ohms .109 volts .816 volts 900 ohms 970 ohms 972 ohms Infinite or immeasurable .001173 amps 1,173 ohms VHS AUTO

  25. Resistor By-Pass • Ballast resistor is used to cut voltage and amperage • Point type ignition first was used on 6 volt systems • When switched to 12 v systems points couldn’t handle added amperage • Resistor was added to prevent burning points • During cranking, battery voltage may drop to 10v leaving around 4 v pushing at “+” of coil • Makes spark weaker when we need it the strongest • Resistor by-pass by-passes resistor while cranking to give full battery voltage to “+” of coil VHS AUTO

  26. Resistor By-Pass Run Chrysler’s Start VHS AUTO

  27. Run Start S I Starter Relay Resistor By-Pass Ford’s VHS AUTO

  28. R S Starter Resistor By-Pass Run GM’s Start VHS AUTO

  29. Resistor By-Pass Questions VHS AUTO

  30. Ignition Timing VHS AUTO

  31. Ignition Timing VHS AUTO

  32. Ignition Timing VHS AUTO

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