Part Five: Ignition Timing

[Hedgerow]

Repped.

It better not be that red stuff you gave me last time..

We’re looking for green over here.

 

[Spladle160]

Does ignition advance make a saw run hotter? If so, why?

Presumably, the further you advance the ignition the longer the hot gases are in the chamber before getting to exhaust leaving more time for heat transfer to the cylinder and piston.

Potentially you build more total pressure with an earlier spark and combustion therefore creating additional friction and heat.

Potentially with the greater pressure and longer burn time you will more completely burn your fuel leaving less to blow out the exhaust and carry heat with it.

But... Julians got the data showing that none of it is to any great degree in the applications and at the levels we're looking at.

 

[VinceGU05]

haven't gone to extremes on the keys/advance. and i've only done this on the 661. Plus this is with the flir. Not the thermocouple. All that said doesn't seem like much? I think the most interesting thing from these results is how the max RPM changes. and of course the times

so are those sizes whats left of the key or what you milled off the key?

 

[Larry B]

Does ignition advance make a saw run hotter? If so, why?

Back in the day i built 5hp Briggs for WKA stock, stock appearing and charity races. When it came to timing advance we would advance timing till we saw head temp go up then back off till normal head temp. If you went a couple degrees more top RPM would drop and head temp shot up. You never heard any pinging or anything abnormal. The target RPM for a stock briggs was 6500. Racer would change gearing to get max speed at 6500. Thing was you could change gearing and still get same max MPH but at different RPM. Stock briggs with timing advance will pull to over 6500 but that is as far as you want to push the stock con rod. I know the Briggs is a 4 stroke and we are talking about 2 strokes running twice the RPM but i wonder if the same would hold true.

 

[VinceGU05]

so are those sizes whats left of the key or what you milled off the key?

checked with the Boss. its whats left of the key.

 

[president]

Like all the other stuff we've talked about, there just isn't any one answer. I don't advance most Echo saws.......or Dolmars. Not too many Huskys either. Almost all the Stihls I do get advanced.

my 024s, wakes up nicely the 044 is great and my old 066
seems to spool up much faster. I also run a 1309 coil from an 046
which is supposed to be a hotrod coil

 

[president]

Really doesn't matter how fast itnis if I never get to put it in wood...

Is there any chance that it being an arctic has anything to do with it? Different coil or anything?

I know there is resistance in rotation of the flywheel with the
generator for the heating elements.weather they are switched on or off

 

[president]

I can tell you that the nova module puts out a hotter spark
than the old trigger unit on an 075

 

[Maintenance Chief]

Earlier in the thread it was discussed about making a control unit for advanced timing , and the little chip that we replace points with is just that . Although the parameters are set in the chip we have essentially deleted the trigger for ignition and replaced it with a digital control.
If we ever do get an adjustable timing controller it would probably use a points coil, which has no input built in.
Just think we'll all be scrambling to find that old 028 wb coil that we boxed ten years ago!" Hhhhmmm? I thought I put it in this cigar box inside this tote labeled Stihl junk?"

 

[Ketchup]

Can an ignition advance burn more fuel? Can it be used to fix an untuneable rich condition?

 

[MustangMike]

I imagine anything not in sync with the engine can be inefficient and waste fuel.

 

[Ketchup]

I imagine anything not in sync with the engine can be inefficient and waste fuel.

Let’s say you port a saw with an extra low intake. Would a timing advance work well with that extra duration?

 

[MustangMike]

No clue!

But in general, more saw porting = more RPM, which necessitates more timing advance.

 

[mrxlh]

You can always use a piston stop and mark the case or flywheel in both directions... then half way between them is TDC.

That would be true TDC, with clearance removed, which doesn’t account for dwell. If you use Steve’s method and watch the dwell (indicator not moving) and zero there, then oppose rotation and come back to that zero, that is true dynamic TDC. With all ignition happening BTDC, it makes Steve’s method more accurate.

 

[mrxlh]

PI taping the flywheel and dividing by 360 will give you the division marks to accurately mark your flywheel (blue layout fluid works great here) for testing. Guessing the average flywheel is ~4” dia, that makes the timing marks .0348” apart.

 

[Ketchup]

That would be true TDC, with clearance removed, which doesn’t account for dwell. If you use Steve’s method and watch the dwell (indicator not moving) and zero there, then oppose rotation and come back to that zero, that is true dynamic TDC. With all ignition happening BTDC, it makes Steve’s method more accurate.

By “dwell” you mean the period where the piston isn’t moving up or down? That seems like several degrees. Do you divide that by two to find TDC? Who’s Steve?

 

[ferris]

So when my no decomp ported 064 is easy to start, I can probably advance it more to get some more power?

 

[Ketchup]

So when my no decomp ported 064 is easy to start, I can probably advance it more to get some more power?

If it’s not advanced already it’s a safe bet.

 

[Newdave]

All you need to do is look at the piston through the spark plug hole or exhaust port to watch it peak out. Center up the dwell if it's measurable.

Endoscope camera and your cell phone should work.. less than $20

 

[ferris]

If it’s not advanced already it’s a safe bet.

It is advanced about half the key.