Part Five: Ignition Timing

[Mastermind]

I think you just described the future, that is if Randy quits squabbling about wordage and go out and find us an electronical genius. Like everything the trick would be making such a thing A) small enough to fit in a power saw and B) tough enough to withstand the vibration.
Surely if the Military can build a shell that can be fired out of a 155mm cannon that has electronic guidance inside, and take that kind of shock. So it would seem something could be worked out. Can we get a budget for this? There really isn't much to the module inside of a coil, or look at the NOVA II modules, pretty small. Surely this could be worked out, after all a rev limiting and single stage advance coils already exists, proving that the signal can be modified.

I delegate that authority over to you.

Find the right electronical genius and get this show on the road.

 

[Stump Shot]

@Mastermind

When you type a word out that you know is right but is underlined in red, just click on it with your mouse to bring up the menu and click on "add to dictionary" now it becomes a word, it will no longer be underlined in red and Webster's is notified of the new usage.

 

[Mastermind]

On the coils with a timing advance curve built in what is the amount of timing it can advance automatically?


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It can't advance really.......it has a retard mode that pulls the timing back closer to TDC for starting. Then at a predetermined RPM it allows the timing to go back to the"normal" setting.

 

[Stump Shot]

I delegate that authority over to you.

Find the right electronical genius and get this show on the road.

I do know one guy, his name is "Sparky" Lol where would you like me to have him send the bill?

 

[Mastermind]

@Mastermind

When you type a word out that you know is right but is underlined in red, just click on it with your mouse to bring up the menu and click on "add to dictionary" now it becomes a word, it will no longer be underlined in red and Webster's is notified of the new usage.

Done.

 

[Mastermind]

I do know one guy, his name is "Sparky" Lol where would you like me to have him send the bill?

Send the bill to @Gentleman

 

[Stump Shot]

It can't advance really.......it has a retard mode that pulls the timing back closer to TDC for starting. Then at a predetermined RPM it allows the timing to go back to the"normal" setting.

"Normal" that's a word you don't get to see thrown around here often.

 

[Stump Shot]

Send the bill to @Gentleman

Do you have a purchase order number to go with that?

 

[Stump Shot]

Do you have a purchase order number to go with that?

Insert sound of Crickets chirping.

 

[mdavlee]

I've advanced some 46 and 66 3/4 of the key. They weren't hard to start there. I'll be playing with some of the 1124 soon and they may not get as much advance on them

 

[moparnut88]

It can't advance really.......it has a retard mode that pulls the timing back closer to TDC for starting. Then at a predetermined RPM it allows the timing to go back to the"normal" setting.

Ok that makes more sense now. I wonder on average what the timing retard is then b4 it goes back to the normal timing? 10* 15* or is every coil a little different. I could see where a 15* retard would be nice for big cc high compression saws during starting.


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[XP_Slinger]

I'd be interested to find a method of seeing what the actual timing advance numbers are for these coils. Can't hook up a timin light to them; so how can it be accomplished?

 

[Chainsaw Jim]

I think you just described the future, that is if Randy quits squabbling about wordage and go out and find us an electronical genius. Like everything the trick would be making such a thing A) small enough to fit in a power saw and B) tough enough to withstand the vibration.
Surely if the Military can build a shell that can be fired out of a 155mm cannon that has electronic guidance inside, and take that kind of shock. So it would seem something could be worked out. Can we get a budget for this? There really isn't much to the module inside of a coil, or look at the NOVA II modules, pretty small. Surely this could be worked out, after all a rev limiting and single stage advance coils already exists, proving that the signal can be modified.

I think it could be quite simple. Have a wired remote electronic ignition system integrated into a control panel with two leads. One lead is a "pick up" for sensing crankshaft position and another connected to the plug. The control panel would have to be simultaneously running a dyno program.
So basically this would be an additional feature on a computerized dyno machine.

 

[Glock37]

On stihl 041 s and other older saws that have a breaker plate a timing is shown hooked up to adjust and set timing
Connect timing light to a 12 volt source and attach the pick up to spark lead
Start saw remove recoil and you can see timing at any giving mark set stock then file key using same stationary mark check timing running
Its a reduced description of how to but i hope you get the idea




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[Terry Syd]

Does anyone know how to do a 'cut and paste' from a PDF file? I've got a PDF file on Stihl ignitions that has a good graph of the timing requirements for a saw. There is also some good graphs in Blair's book, especially on flame propagation.

 

[Terry Syd]

I can get the text from Blair, but the graphs are very helpful. Essentially, there is about a 10 degree lag from the spark until the flame propagation really takes off. The best power for the engine occurs when the engine is timed so that around 10 degrees ATDC, 50% of the mixture has been burnt. From Blair -

The analysis of the cylinder pressure trace for the heat release rate is shown in Fig. 4.4, and that for the mass fraction burned is shown in Fig. 4.5. It is quite clear that there is an ignition delay period of 10° before the heat release becomes manifest in the combustion chamber. The heat release rate peaks at 10° atdc, 20° after the heat release commences properly at 10° btdc. In Sec. 4.1.1, where this particular example was discussed in terms of flame travel time, it was adjudged that the flame had traveled throughout the chamber in 33° crank angle. It can be seen from Fig. 4.4 that this coincides with the time from ignition to the peak of the heat release rate, and that position also coincides with the point in Fig. 4.5 where 50% of the mass fraction was burned. The position for the 50% burn point is about 10° atdc.

 

[Backtroller]

This would be cool to play with if it could be modified to work

 

[moparnut88]

View attachment 68849 This would be cool to play with if it could modified to work

We could rig that up but where would you put it all at? And I got to thinking. How many volts do the coils on the saws put out? If one could rig up the mad to work then we could go with a really good coil and adjustable!


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[Terry Syd]

There have been very good variable ignition timing modules on bikes since the late 1980s. I'm surprised that the saw manufacturers haven't developed their own as they could be incorporated into the coil and wouldn't add any weight to the saw.

I remember looking at the spark curve of a KTM module where the timing was all over the place as it followed the required timing for use on a piped engine. When the engine was just below where the pipe came in and out of sync with the pipe, the timing nearly doubled, then as it came on the pipe the timing slowly retarded as charging efficiency increased, then as it moved past peak torque the timing increased until it hit max revs and dropped off quickly.

A saw engine isn't as extreme in the way the cylinder is charged, but there is a fair bit of broad range power that could be realized by moving away from a fixed ignition timing and having a timing that followed the requirements of the engine.

 

[junkman]

I got this over 20 years ago for tuning my 440 engine,it can advance and retard timing somehow when running ,looks like they used to have a 2 cycle adapter option ,wonder if would work on a saw ?