2001VHS AUTO1 IGNITION TIMING AUTO 2

2001VHS AUTO2 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

2001VHS AUTO3 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 But it will take some Time to burn!

2001VHS AUTO4 Ignition Timing Engineers generally agree that we need the biggest push down on the average piston around 23 o ATDC

2001VHS AUTO5 Overadvanced Timing (too soon) Causes Detonation Second explosion of A/F after plug lights Hard cranking (balking) More of one type of emission

2001VHS AUTO6 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

2001VHS AUTO7 Ignition Timing Lets say this engine takes 4 mS to burn the A/F to get good pressure and we want the big push at 23 o ATDC Lets say this engine is running at 1650 RPM (write it down by the picture) Look at this picture In your notebook (top left picture) 23 o

2001VHS AUTO8 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 360 o in a circle so 360 times 27.5 = about 10,000 o per second of crank There are 1000 mS per second so 10,000 divided by 1000 = 10 o per mS 10 o per mS times 4 mS = 40 o I got it, At 1650 RPM the crank will move about 40 o in 4 mS

2001VHS AUTO9 Ignition Timing 40 o Write in 23 o ATDC Calculate how many degrees before TDC the spark will need start to get the big push at 23 o ATDC Write in answer here

2001VHS AUTO10 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 17 o BTDC the BIG PUSH will happen too late Lets calculate

2001VHS AUTO11 Ignition Timing 2500 divided by 60 = RPS times 360 = 15,000 degrees per second 15,000 divided by 1000 = 15 degrees per mS 15 times 4 mS = 60 degrees 17 o BTDC 2,500 RPM Calculate when the big push will Happen and fill in on drawing 43 o ATDC TOO LATE

2001VHS AUTO12 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

2001VHS AUTO13 Ignition Timing 23 o ATDC At 1650 RPM 17 o BTDC 40 o

2001VHS AUTO14 Ignition Timing If we are going to maintain the big push at 23 o ATDC at 2500 RPM, Calculate where we are going to have to advance the timing too? 23 o

2001VHS AUTO15 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?

2001VHS AUTO16 Vacuum Advance Vacuum advance rotates points on breaker plate around The distributor cam to advance when the points open and close

2001VHS AUTO17 VACUUM APPLIED

2001VHS AUTO18 Vacuum Sources #1 Venturi RPM RPM RPM Venturi not strong Enough to use for Vacuum advance Find page in notebook 1 #2 Ported 2 #3 Manifold ” O-1” 15-20” 1-3” 13-20” 3-5” 0-2” 0” 19-26”

2001VHS AUTO19 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 3 o of dwell

2001VHS AUTO20 Mechanical Advance Mechanical (centrifugal) advance advances the distributor cam to the distributor shaft to open points sooner

2001VHS AUTO21 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

2001VHS AUTO22 Manual Scale Meter

2001VHS AUTO23 MILLIONS SIX WHOLE NUMBER THOUSAND THREE WHOLE NUMBER THOUSANDTHS (mili) THREE DECIMAL MILLIONTHS (micro) SIX DECIMAL

2001VHS AUTO24 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 amps 1,173 ohms

2001VHS AUTO25 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

2001VHS AUTO26 Resistor By-Pass Run Start Chrysler’s

2001VHS AUTO27 Resistor By-Pass Run Start Ford’s SI Starter Relay

2001VHS AUTO28 Resistor By-Pass Run Start GM’s RS Starter

2001VHS AUTO29 Resistor By-Pass Questions

2001VHS AUTO30 Ignition Timing

2001VHS AUTO31 Ignition Timing

2001VHS AUTO32 Ignition Timing