Ignition Timing Advance or Retard The Why's and How's

[VTRDark]

First off you should know that there are two types of timing, 'Cam timing' and 'Ignition timing'. Though the two are closely related don't confuse the two and for the purposes of this write up I will be concentrating on Ignition timing. I shall try and keep things as simple as possible without going into to much technical detail.

To understand what's happening we have to first know whats going on inside the cylinder. We also have to appreciate the fact that the valves don't open and close instantaneously but overlap each other to a certain degree throughout the cycles. This is due to the physics of gas flow and the valves will have their opening and closing times controlled via the cams. We also have to understand that the explosion inside the cylinder is not instantaneous as is often misunderstood and is more of a 'controlled burn'. The point of igniting this charge 'Ignition Timing' is vital to the smooth running and longevity to the engine along with fuel economy and emissions control as well as getting the maximum performance out of an engine. It's all about finding an even balance or sacrificing one for the other.


THE FOUR STROKE CYCLE


Diagram of the Basic Four Stroke Cycle

1. Induction (suck)
The Exhaust Valve is closing and the downward movement of the Piston begins the Induction stroke. The Inlet Valve is open allowing a fresh charge of vaporised fuel/air mixture to be drawn into the cylinder from atmospheric pressure. At the same time the downward movement of the Piston reduces pressure and creates a vacuum. The fresh charge lags behind the Piston on it's way down and begins to catch up as the Piston slows down towards the bottom of it's stroke. When the Piston nears the bottom of it's stroke, Bottom Dead Centre (BDC) the Inlet Valve then begins to close.

2. Compression (squeeze)
With the Inlet Valve closing the gas flow continues to fill the cylinder with a fresh charge until the Piston is on it's way back up from the momentum of the crankshaft and flywheel. After Bottom Dead Centre (ABDC) and with the Inlet Valve fully closed we then have a sealed cylinder filled with the vaporised fuel/air mixture ready to be compressed as the Piston moves upwards increasing pressure towards Top Dead Centre (TDC). As the Piston nears the top of the stroke some degrees Before Top Dead Centre (BTDC) the Spark Plug then Ignites the charge in a controlled fashion which rapidly expands spreading itself across the Combustion Chamber as it moves onto the Power stroke.

3. Power (bang)
The charge continues to expand After Top Dead Centre (ATDC) until it reaches maximum peak pressure which then forces the Piston back down making the rear wheel turn. At this stage the wasted fuel/air mixture ideally should be completely burned and needs to get forced out to make room for a fresh charge. During the downward movement of the Piston the increasing volume lowers pressure while the Exhaust Valve is still closed, though this is still higher than atmospheric. As the Piston nears bottom dead Centre (BDC) the Exhaust Valve begins to open releasing the pressure even more so in the cylinder as it moves onto the Exhaust stroke.

4. Exhaust (blow)
With the Exhaust Valve open the Piston moves back upwards forcing the wasted fuel/air mixture up and out the Exhaust Valve increasing gas velocities along the Exhaust Pipe. As the Piston nears Top Dead Centre (TDC) the velocity of gases along the exhaust pipe creates a partial vacuum inside the cylinder and the Intake Valve begins to open. As soon as pressure drops below that of the intake a fresh charge of vaporised fuel/air mixture will begin to be drawn in ready for the cycle to begin all over again. By opening the Inlet Valve before the Exhaust Valve has closed, the momentum of exhaust flow will help draw the fresh charge in which is drawn towards the closing Exhaust Valve. This ensures that the combustion chamber is thoroughly scavenged and cleared of any waste gases. Ideally the Exhaust Valve should close as the fresh fuel/air mixture reaches it.


The above Diagram shows the Point of Valve Open and Closing times

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http://www.youtube.com/watch?v=-dwHUz7nWPA

Controlled Burn
Now let's look at how the controlled charge burns across the combustion chamber. When the spark ignites the vaporised fuel/air mixture it spreads itself from the centre of the triggering device which should be at the spark plug electrode which ignites the charge which then spreads across the mixture. You will often hear this combustion progression across the cylinder referred to as the flame front. Visualise the way you would blow up a ballon or blowing a bubble, it starts off slowly and as it expands it increases in speed spreading itself out like the ripples on water as a stone lands when thrown. This all takes place within milliseconds.


This Diagram illustrates the Progression of the Burn

This could be compared to the fuse on a firework which may be easier to understand. When you initially ignite the fuse there is a moment where there is a pause in the sparks before it starts to travel along the line. This starts off at a slower burn rate and as it nears the firework it reaches the faster "quick match" fuse and burns more rapidly, reaches the gunpowder and sets of the explosion.

[youtube][/youtube]

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[VTRDark]

IGNITION TIMING

Ignition timing on the VTR 1000F as standard is set to fire the Spark Plug at 15° Before Top Dead Centre (BTDC) at idle as the Piston moves up on the Compression stroke and advances to 42° BTDC at 9,500 rpm.



The point of igniting the charge Before Top Dead Centre (BTDC) is to account for the timing (expansion) of the burn. The complete burn should ideally reach maximum peak pressure at around 10°-20° degrees After Top Dead Centre (ATDC) on the power stroke when the optimum point of leverage is on the piston connecting rod to crankshaft angle.

If the spark ignites the charge too early (too advanced), the pressure from the ignited mixture will hit the piston while it's still travelling up on the compression stroke and will be wasted forcing the piston downwards before it reaches the end of its stroke. The combustion is basically trying to push the piston backwards creating a lot of extreme heat. This detonation is bad for the engine. There's also pre-Ignition which is the spontaneous ignition of the charge from another heat source before the spark plug has fired. This is far worse than detonation and can write off the engine rather quickly. I shall explain more on these two later! On the other hand if the spark ignites the charge too late (too retarded), the pressure from the ignited mixture will occur later and will be wasted chasing the piston back down on the power stroke.

If given a constant combustion rate then the rate of the burn remains the same but how fast the piston moves and pressure changes does not. For this reason the point of igniting the charge needs to be sooner, more advanced as piston speed increase so the point of maximum peak pressure After Top Dead Centre (ATDC) occurs around the same position. This is what ignition timing is all about, setting the firing of the spark plug so the vaporised fuel/air mixture is fully burning at the right point to provide maximum power. Hence you can see why the spark needs to ignite the charge sooner, more advanced, as engine speed increases and retarded as engine speed decreases, it needs to ignite later. The changing of the exact point of firing the spark plug is controlled by the Ignition system, mainly the Ignition Control Module (ICM) which contains the Ignition map advance curve and to some degree the Throttle Position Sensor (TPS).

Detonation
Detonation, also known as 'spark knock', 'rattle', 'ping', 'pinging'. Whilst advancing the ignition can produce more power, too much advance is even worse. If the spark occurs too early then the maximum peak pressure occurs too early, Before Top Dead Centre (BTDC) as the piston is still rising on the compression stroke.


Bent Connecting Rod from excessive forces working against the Piston

Detonation is brought about by too much compression. If you take a bicycle hand pump for example and pump it fast enough you can feel the heat generated as it's compressed. So lets put the fuel/air mixture into a closed cylinder and compress it quickly, this then generates enough heat to light the charge which is basically what detonation is though this normally takes place once the spark plug has already ignited the charge. When a spark plug ignites the charge it burns quickly but does not explode and has a definite progressive burn period as previously explained. The timing of the Spark is set so maximum peak pressure occurs when the crank and connecting rod are at right angles to each other after the piston has passed Top Dead Centre (TDC) on the power stoke as the piston is on it's way back down which then transfers that power to the road wheels. Detonation is not a burn but more of an explosion. Essentially all the fuel/air is burned off instantaneously. That explosion creates supersonic shock waves within the combustion chamber that ring back and forth around the chamber. It's these shock waves that we hear as a 'ping', 'rattle' or 'knock'. If you have ever driven/ridden under load up a hill in too high a gear then this is the same sound that you hear. Some modern day vehicles will have a knock sensor built into the ignition system that listens out for detonation and adjusts the timing map accordingly.


Excess Carbon build-up and Pitting from Shock waves

Not only will the extreme pressure put unnecessary strain on the rising piston and other components, but the extra heat generated too close to the top of the piston crown along with the shock waves can erode the aluminium head and piston crown. It's quite common for an engine to run with some light detonation but too much over a period of time is not good and can eventually cause engine failure.

Detonation can be caused, for example, by:

• Lean fuel mixture
• Fuel octane too low
• Improper ignition timing
• Lugging the engine
• Excessive milling of heads or block, which will increase compression ratio.

Pre-Ignition



Pre-Ignition is like detonation but less related to timing. Something else is causing the charge to ignite. This is often caused by either too low an octane fuel which has an increased tendency to auto ignite or a hot spot in the combustion chamber. This can be in the form of excess carbon build up on the piston or valves or even the plug itself if hot enough to spontaneously ignite the fuel/air mixture present in the cylinder.


Excess Carbon build-up on Piston Crown

Pre-Ignition is a silent killer as you may not necessarily hear it as a 'knock', 'ping' or 'rattle' but may notice a roughness in running. What makes pre-Ignition bad is that it ignites the mixture before the spark plug has fired, usually After Bottom Dead Centre (ABDC) as the piston continues to rise fighting the increasing pressure of the burning mixture. This then reduces power and generates excess heat that the piston and combustion chamber then absorbs and then melts and/or burns a hole in the piston crown and/or melts valves. Not a good situation and can happen very quickly without much warning.

Pre-Ignition may be caused, for example, by:

• Carbon deposits
• Spark plugs too hot a heat range
• Spark plugs not firmly seated
• Detonation or the condition leading to it
• Sharp edges in the combustion chamber
• Valves operating at higher than normal temperature because of excessive guide clearance or improper seal with valve seats.
• Overheating


Severe Engine Damage caused by Pre-Ignition

Don't let what I have said about Detonation and Pre-Ignition scare you as you would have to do something quite extreme for it to happen but it is something to be aware of. Honda built these engines with longevity and emissions in mind so therefore there is some room for error and tolerances are not that precise which creates a safety margin.

For more info on Detonation and Pre-Ignition in more depth see the following article:

Engine Basics: Detonation and Pre-Ignition

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[VTRDark]

IGNITION SYSTEM

The VTR100F ignition system is a computer controlled digital transistorised with electronic advance system and to be a little less specific Transistorised Controlled Ignition (TCI) system. So what's that mean? I hear you ask. Let's break this down to the main individual components and what exactly they do.


Ignition System Wiring Diagram

Ignition Pulse Generator
This is basically a crankshaft position sensor and is where the piston position according to revs is taken from and for those of you that remember could be compared to a more conventional system (Kettering design) where mechanical points where used inside a distributor. The ignition Pulse Generator consists of two components a magnetic pulse pickup sensor, similar to a Hall effect sensor except for it's not powered, which is mounted on the inside of the clutch casing and a rotating Ignition Rotor plate which is sometimes known as an Ignition advancer or retarder and is mounted directly off the crankshaft.



The Ignition Rotor plate is like a cog or spurred gear wheel with teeth, and as it spins these teeth pass the magnetic Pickup Sensor which breaks the signal each time one passes, this in effect is like a switch switching on and off and breaks or interrupts the magnetic field which in turn alternates from a high to low or on off, though technically it's an analog signal and never really switches off while it's running. This then sends a generated low voltage AC signal pulse to the brains of the operation, the Ignition Control Module (ICM) where it calculates the necessary amount of advance required according to the revs, speed of piston travel. On a side note; this is also where ICM gets it's signal from for the rev counter.



The standard timing for the VTR1000F is fixed at a starting point of 15° Before Top Dead Centre (BTDC) at idle via the Ignition Rotor Plate. Aftermarket Ignition advancers and retarders are available so for example if you was to install a plus 4 Ignition advancer then the timing would start at 19° BTDC and if you installed a minus 4 Ignition retarder then the timing would start at 11° BTDC.



Throttle Position Sensor (TPS)
The density of fuel/air mixture (charge) in the cylinder needs to be taken into consideration with how much advance is required. The spark plug needs to fire earlier when less dense at closed throttle (idle speed) or part open throttle (steady state cruise) operation. At wide open throttle (WOT) the fuel/air mixture is most dense and combustion is very rapid so no additional advance is required.



The TPS monitors your throttle position via the Carburettor throttle plate (butterfly flap) which is directly related to throttle position. The TPS then sends a signal back to the brains of the operation, the Ignition Control Module (ICM) where it calculates the necessary amount of advance required according to throttle position.

Engine Coolant Temperature Sensor (ECT)
Temperature also has an effect on the density of the fuel/air mixture. The hotter things are the less dense things get and the colder things are the more dense things get. Temperature also has an effect on the speed of the burn. More heat means that the fuel/air mixture (charge) is gong to burn faster whereas if colder it burns slower. The Engine Coolant Temperature sensor is mounted on the Thermostat housing and also sends a reading back to the brains of the operation, the Ignition Control Module (ICM).

Ignition Control Module (ICM)
This is the brains of the operation, the computer, ECU if you like, that inputs the readings from above, makes it's calculations and adjusts the Ignition Advance curve accordingly. The ICM not only contains the base ignition curve but also controls other things like the speed limiter.


Diagram of the Base Advance Curve

Once the Ignition Control Module (ICM) has worked out it's calculations and adjusted the advance curve it then sends a signal to the Converter Unit which controls the firing output to the Coils which then fires off the Spark plugs. Unfortunately we have no way of accessing the data on the Ignition Control Module without highly specialised equipment and it is a sealed unit.

Converter Unit
The Converter Unit, which is sometimes known as an Igniter or Amplifier, is basically a transistorised switching device for controlling the firing pulse to the Coils. It seems the Converter Unit on the VTR is unlike a conventional system that would output 12V DC and takes the low voltage AC signal from the Ignition Pulse Generator via the Ignition Control Module (ICM) and amplifies the signal to a converted peak voltage of 100V minimum. This is known as the primary switching current or low tension (LT) circuit which is then sent to the Coils primary winding. Note on later models I believe the converter unit also contains the HISS security system.

Ignition Coils
The Ignition Coils are the heart of the ignition system and produce the high current voltages required to make the current jump across the gap on the spark plug. An Ignition Coil consists of two copper windings, a smaller primary and a larger secondary sometimes known as low tension (LT) and high tension (HT) that wrap around an iron core. There is also a high voltage terminal where the High Tension (HT) lead connects and then on to the Spark Plug.



When the primary low tension voltage from the Converter Unit is switched on and flows through the Coils outer primary low tension windings the iron core becomes a strong electromagnet. This then creates a magnetic field that encloses the inner secondary high tension windings. When the Converter Unit switches off the signal to the coils primary windings the magnetic field then collapses across the secondary windings. As the magnetic field collapses a high electrical voltage is induced into the secondary high tension windings which can be anything up to 50,000 volts. This then passes from the coil to the Spark Plug and creates a spark that ignites the charge.



Spark Plugs
The Spark Plug is last in the chain-of-command and after it fires there is no turning back. It consists of a porcelain insulator in which there is an insulated centre electrode supported my a metal outer casing with a grounded strap.


Diagram of Spark Plug Cutaway

The Spark Plug uses the Ignition Coil high voltage to ignite the vaporised fuel/air mixture. It requires anything between 5000 - 15,000 Volts to make the current jump the gap at the electrode. This is lower than the potential output of the Coil owing to many variables including losses along the way. When the current is released from the Coil it searches for a place to ground out much the same way as lightening from the sky is seeking ground. Hopefully this released current finds the gap between the centre electrode and ground strap on the plug.



Spark Plugs have and run within a specific heat range. This determines how hot the plug will run and it's ability to transfer heat away into the cooling system that runs around the cylinder walls. A hot Spark Plug prevents heat transfer into the cooling system and will also elbow off any deposits that build up. This provides a self-cleaning action. A cold Spark Plug operates at a cooler temperature and helps prevent overheating and pre-ignition. The only time you should change a Spark Plugs heat range is when abnormal engine or operating conditions exist.



If the plug runs too cool, sooty carbon deposits build up on the insulator around the centre electrode. This deposit could soon build up enough to short out the plug, then high voltage surges would leak across the carbon instead of producing a spark across the plug gap. Using a hotter plug will elbow the carbon deposits off or prevent it from forming in the first place. Spark Plugs can be used to help determine the running condition within the cylinder by the colour and condition of the insulator and electrodes, though this is getting harder to read with some of todays modern day plug technology.

For more information on Spark Plugs please read the following:
http://www.sparkplugs.co.uk/pages/manuf ... -plugs.htm


There's a lot more technical detail as to how the Ignition system works, Iv'e not even mentioned 'dwell', or 'turbulence' but wanted to keep things as simple as possible without going into too much depth. The purposes of this write up is to give you a better understanding of what's going on that helps with troubleshooting/diagnosing problems and knowing where to start looking. Iv'e purposely not gone into tests that can be done to individual components as most of this can be found in workshop manuals.

Next week Cam Timing

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[StuartWags]

Thats good

Can you do multishot injection as well

[StuartWags]

Thats good

Can you do multishot injection as well

just kidding

[sirch345]

WOW you have been a busy boy Carl
Nicely done with the added photo's. I like the spark plug Gif
The 100V on the LT side of the coil is something I hadn't realised our bikes have.

Keep up the good work,

Chris.

[lloydie]

That will give me something to read when I'm in the bog !! :-)

[gl_s_r]

That will give me something to read when I'm in the bog !! :-)

Can't wipe your elbow with it after though... not like the old days when it was all on paper.

[lloydie]

I can print it off :-)

[VTRDark]

Well if your going to use it as bog roll make sure you get the timing correct otherwise sparks will fly when the other half catches you

Nicely done with the added photo's. I like the spark plug Gif

That was pilfered The 100V was a shock to me, not what I was expecting.

(:-})

[MK_WF]

Nice writeup.

I'd like to add the information that Ignitech offers a plug&play replacement ignition controller for the VTR1000F.
The trick is that they offer adaptor harnesses to match the bikes stock connectors:
http://www.vtr1000.de/forum/attachment. ... 1440848766

The price is pretty competitive: around 180 Eur incl. shipping.

Above you note an ignition advance between 15 at idle and 42 degrees at 9.500.
As far as I know Jan Matous from Ignitech has been sent a Honda unit and reverse engineered the ignition map.
This is what he found and what's delivered with the unit I purchased:
http://www.vtr1000.de/forum/attachment. ... 1440848766

It only contains values from 5 to 39 deg.
The bike is running fine but I feel a slight midrange loss compared to before.
Using 5 deg in the near idle range is very beneficial for smooth cruising in build-up area.

Is there anyone having experience with optimized ignition maps for the VTR and may shed some more light on what would be feasible values ?
Or even better: Is there someone who can share Ignitech .ign or Megasquirt .msq files?

[VTRDark]

@MK_WF thanks for that post. Some great info there and very relevant to the thread.

(:-})

[andrewmagas]

hi it seams i have early timing due to the ignition pulse sprocket no tin place

can anyone point me with some nice picture of how to align it in place
manual sais
Install the primary drive gear assembly and ignition
pulse generator rotor by aligning the wide grooves
with the wide tooth.

[VTRDark]

pulse sprocket no tin place

Not in place Got any pics

The primary drive gear has a quietening gear with springs holding them together and is a nightmare to piece back together if separated. You want to hold these together with some cable ties/zip ties to hold it all together as one piece.

As for the Ignition timing rotor itself it can only go on one way because of the way the inner splines are cut.

[andrewmagas]

after the accident i had my clutch cover damaged and when i opened the cover i found that sprocket and i thought it is also damaged as it doesn' t look like factory made with teeth missing
so i removed it and only after on the web i found it is all correct so nothing was brocken there
it was a nightmare to place it back
and i think i did somethiing wrong
so will get some pictures and hope you guys can tell me what's wrong about it