ignition timing on modded saws

[trappermike]

You usually won't hear detonation in a 2-stroke,but if the ignition is too advanced you may find the piston crown melted,or signs of extreme heat and/or aluminum residue on the spark plug.

 

[064AV]

Thanks to my ADD-like attention to spatial orientation, I must correct my last post. Although my goal is to advance my timing, it was (much like me) retarded by my flywheel swap. In which case, I do have room to move my coil to adjust my timing as opposed to key modification.:bang:

 

[trappermike]

Most chainsaw motors are far from extreme high-output designs like some motorcycles and others,having fairly primitive cylinder ports,carb size,no pipe etc. In most cases that I've worked on(Except race applications) they are not of such high output that ignition retard is needed,most motors will be happy with a little advance,or if built to a higher level the stock timing has not proven detrimental in most cases.
Yes high output designs today often have an ignition curve with the timing retarding as rpms increase to higher levels but these motors are on a much higher design level. And it's also common for some engines to have an advance curve-the timing is retarded at low revs for easy starting and then advances as revs build.
Only some tweaking and testing is going to prove what works best on your particular motor,and you will want to keep a close eye on what your spark plug looks like(Color and signs of excessive heat) to look for warning signs,also peeking in the spark plug hole or looking thru the muffler at the piston crown to look for signs of excessive heat and see flow patterns in residue on the crown is another favorite way cyclists and snowmobilers monitor tuning.
Higher output generally requires colder spark plug heat ranges,and in higher output engines extended tip spark plugs are avoided and can actually cause piston damage in some cases. Citing Bosch spark plugs as an example,I like to use the WS5F plug in modded work saws and WS5E(Non-extended tip) in higher output saws. For race saws unfortunately there is not much available for racing plugs in 3/8" reach common to saws,so 1/2" plugs can be used with an aluminum spacer under them,then you have a wide choice of plugs available-platinum,iridium,etc.

As for timing,since saws generally don't have any timing marks to run a light on them I will make my own timing marks on the motor,first to discover the actual timing of that motor and to give me a reference point to work from.
-I will mount a degree wheel on the crankshaft and simply as a starting point make my own timing marks with a felt pen or paint pencil at 25 degrees BTDC(A general starting point,and a figure common to some decent output motors),try to make a mark on a flywheel fin and one on the crankcase for instance. Try to find a place where you can see your marks with the starter cover on.
-Then you can run the motor with a timing light and see where the timing actually falls,make a new mark indicating that point,and then check with your degree wheel to discover where your engine is actually firing at BTDC. Now if you want to alter your timing you know exactly where you are.

All the mods you do to your motor- porting,compression,carb,pipe,fuel,etc.,will dictate the actual ignition timing your engine will require or tolerate in the end. And like most people here say,more advance generally will pick up power if the timing is not far enough stock. I've rarely seen a stock chainsaw damaged by ignition over advance...
Sometimes the stock timing is not advanced enough for optimum output because the manufacturer has it retarded for easy starting.

 

[stihl038x2]

Here's how I advance the timing. I put the degree wheel on, find TDC w/the flywheel on, mark TDC with a fineline marker on the F/W & correspondingly on the side of the jug. I advance the crank the amount I want then mark that location in line with the TDC mark from the F/W. I pull the flywheel (with the degree wheel still on), turn the motor back to TDC (degree wheel), reinstall F/W rotating it to my advance mark. I put a tiny dab of super fine polishing paste (toothpaste will work), to lock on the F/wheel. You can double check that things haven't moved by cross referencing the degree wheel to your marker lines.

Steve

 

[lone wolf]

Here's how I advance the timing. I put the degree wheel on, find TDC w/the flywheel on, mark TDC with a fineline marker on the F/W & correspondingly on the side of the jug. I advance the crank the amount I want then mark that location in line with the TDC mark from the F/W. I pull the flywheel (with the degree wheel still on), turn the motor back to TDC (degree wheel), reinstall F/W rotating it to my advance mark. I put a tiny dab of super fine polishing paste (toothpaste will work), to lock on the F/wheel. You can double check that things haven't moved by cross referencing the degree wheel to your marker lines.

Steve

Do you use a dial indicator for TDC

 

[wigglesworth]

A part of what led me to the issue of timing was noticing that unlike my 064 or old 066, a half-*ss pull on my 046 will result with a violent removal of the starter handle from my hand. So I am in the process of replacing the 064 alloy flywheel with an 046 poly flywheel. As near as I can tell, this advances the timing by at least one half the width of the woodruff to maybe the full width. This is more than I can correct by moving the coil, so I'm working on modifying/relocating the key. I've got the flywheel on, and the saw is running; however I'm concerned with detonation and top end damage under load. I've heard detonation in a V8, what will it sound like in a chainsaw? I'm running premium fuel so I should have the ability to run more advance without detonation.

U saying you used an 046 poly flywheel on an 064? Thats a new one on me....

 

[Meadow Beaver]

Interesting opcorn:

 

[one.man.band]

timing light: could you folks that use one for saws, tell me what brand you use? i have never had good luck with 'dial back' timing lights. my regular light, even when used for motorcycle applications is very difficult to read at higher rpm. looks like one solid flash. being that the timing is fixed for most saws, at what rpm do you get the good reading? +/- 2700 rpm idle speed?


the bikes i have seen on the dyno benefited more from a retard than advance at high rpm's. that gave the highest #'s. on the road however, an advance in timing was needed to account for rider and bike weight for best performance. a run under steady throttle, up a long steep grade ended up being the determining factor where to set final timing. (a very slight ping). pinging during acceleration is not as important, and only lasts a few seconds at most. would the same idea transfer to saws in regard to load on motor when buried in a log? curious.

 

[Jacob J.]

A part of what led me to the issue of timing was noticing that unlike my 064 or old 066, a half-*ss pull on my 046 will result with a violent removal of the starter handle from my hand. So I am in the process of replacing the 064 alloy flywheel with an 046 poly flywheel. As near as I can tell, this advances the timing by at least one half the width of the woodruff to maybe the full width. This is more than I can correct by moving the coil, so I'm working on modifying/relocating the key. I've got the flywheel on, and the saw is running; however I'm concerned with detonation and top end damage under load. I've heard detonation in a V8, what will it sound like in a chainsaw? I'm running premium fuel so I should have the ability to run more advance without detonation.

U saying you used an 046 poly flywheel on an 064? Thats a new one on me....

I'd have to see this to believe it. I did mock up an 046 flywheel on an 064 crank once to see if it could be made to work, and it's a possibility. However, there were issues with the starter pulley on the 064 starter and the starter cup being smaller on the 046 flywheel.

 

[trappermike]

As for timing lights I think that whatever one works for you is the right one,if your own doesn't work well try a couple of buddy's lights to see if they work better. Probably a Snap-on light will work well if you can afford one. I find that the timing light's pickup sensor that attaches to the plug wire is the key,some work better than others. The timing light I use now wasn't expensive,a cheapy actually, but works fine,others had trouble "picking up" the spark signal.

On another note,I once tried using "Surface Gap" spark plugs,but I found that since saws don't have actual CDI ignition they didn't have the power to fire them,the saw would idle ok but would misfire badly as soon as I revved it up. But I find that the "Fine wire" type race plugs,Platinum,palladium etc. by NGK,Bosch etc. work well. I would be interested to test the "Triple Fire" type plugs if I could find one with the correct reach and heat range,but I'm not sure saw ignitions have enough power to fire them well. Has anyone tried them?

 

[064AV]

U saying you used an 046 poly flywheel on an 064? Thats a new one on me....

I'm working on it. The taper on the 064 crank is the same as the 046 (460?) Poly flywheel I've got. The key location doesn't match, and there is a lip on the case side of the flywheel that I had to remove in order to clear the 064 case. The saw ran, but I need to correct the timing

 

[Jacob J.]

I'm working on it. The taper on the 064 crank is the same as the 046 (460?) Poly flywheel I've got. The key location doesn't match, and there is a lip on the case side of the flywheel that I had to remove in order to clear the 064 case. The saw ran, but I need to correct the timing

What about the starter issue? The starter cup on the 046 flywheel is too small for the rope rotor and starter pawls on the 064 starter. Did you modify the 046 rope rotor and then put it into the 064 starter housing? There's a lot of monkeying around needed to get a working starter with that set-up.

Like I said, I mocked it up but the starter issues kept me from following through.

 

[064AV]

What about the starter issue? The starter cup on the 046 flywheel is too small for the rope rotor and starter pawls on the 064 starter. Did you modify the 046 rope rotor and then put it into the 064 starter housing? There's a lot of monkeying around needed to get a working starter with that set-up.

Like I said, I mocked it up but the starter issues kept me from following through.

I opened my mouth...I guess it's time for my first thread...bare with me, I've gotta figure out how and get pics of the procedure...

 

[one.man.band]

As for timing lights I think that whatever one works for you is the right one,if your own doesn't work well try a couple of buddy's lights to see if they work better. Probably a Snap-on light will work well if you can afford one. I find that the timing light's pickup sensor that attaches to the plug wire is the key,some work better than others. The timing light I use now wasn't expensive,a cheapy actually, but works fine,others had trouble "picking up" the spark signal.

On another note,I once tried using "Surface Gap" spark plugs,but I found that since saws don't have actual CDI ignition they didn't have the power to fire them,the saw would idle ok but would misfire badly as soon as I revved it up. But I find that the "Fine wire" type race plugs,Platinum,palladium etc. by NGK,Bosch etc. work well. I would be interested to test the "Triple Fire" type plugs if I could find one with the correct reach and heat range,but I'm not sure saw ignitions have enough power to fire them well. Has anyone tried them?

my regular light is a old craftsman, (professional inductive timing light #161.2134). metal case. to give y'all an idea of actually how old...it was made in the USA. works well for other applications.

since i have never attempted to time motors this small. realize that it will require 4 hands... or 2 hands and some kind of test stand to hold the saw. the clamp on the light which clamps around the spark plug wire is rather large. won't be able to move at about much (or at all), on the saw's short plug wire.

don't have any idea how many mJ a saw's ignition put's out. would think that finding a plug that fire's with the lowest voltage would help, but how to find that out is the question... other than getting a handful of plugs to try. typical CDI's lose spark power as the RPM's increase. magneto's do not. the spark from my saw is blue and resembles a point's style spark. the magneto spark from my bike fairbanks-morris is a huge yellow ball, even when spun on the bench by hand. no comparison between the two at all. not familiar with karata magneto ignitions which have an external coil.

 

[boron1034]

YPVS = Yamaha Power Valve System

Having a background as a Powersports Tech (Motorcycles, ATV, Snowmobile, etc) I just wanted to point out that the RZ350 engines use a powervalve setup. This will add a whole new dimension to the ignition timing as far as the tuned pipes affect on power vs. rpm. The powervalves will dramatically affect cylinder scavenging and power at lower/mid rpms by having adjustable exhaust port height/area. I think that you will find that two strokes with powervalves may have different timing curves than those without. This may not be the best Timing Curve to use as an example. Although with a saw you are really more concerned with power in a smaller RPM range at high Revs. I do agree that the factory ignition advance is almost definetly not going to be optimal with a tuned pipe on a saw. This is my first post just joined maybe I should have started just with "Hi":smile2:

You are right. Combustion chamber style and rpm are goverining factors in ignition advance. There is at least one more important factor: cylinder filling (i.e. volumetric efficiency).

Either in 4-stroke or 2-stroke engines required ignition advance is reduced when cylinder filling is increased.

In 4-stroke engines this is evident by looking at turbocharged engine's ignition advance tables when the engine is on turbocharger boost. Ignition advance gets reduced by about 15 degrees when turbocharges comes into play.

In 2-strokes we have the same "turbocharger" effect through tuned pipe.

Stock saws have only simple exhaust muffler box which has zero effect in elevated cylinder filling. I believe manufacturers have engineered ignition advance to max out power delivery with this combo.

Slap on tuned pipe on such saw, and I believe our stock ignition timing is holding back our saw. More power can be had by retarding the ignition event.
What stock timing does, is to ignite combustible mixture far too soon, and pressure peak exists too soon, where crankshaft is not yet in it's most ideal position (at about 17 degrees past TDC).

Please have a look at enclosed Yamaha 2-stroke motorcycle engine ignition advance curves. By my wild guess, the tuned pipe seems to come on at about 11 000rpm and finishing at about 14 000rpm. Have a look at ignition advance requirements what the tuned pipe does to the engine.
Ignition advance requirements are way different at lower rpm's when the engine is not "on the pipe".

There are many different ignition curves. I believe that this is a comparison between different available Yamaha ignition boxes, suited for different combos of tuned pipes and differently ported cylinders.

I believe many piped saws would benefit from retarding the ignition sensor by say 5 degrees (or perhaps even more).

 

[trappermike]

I'll try to describe the differences in some electronic ignitions for interest sake. We can think of an ignition as electronic if it uses an electronic system to trigger and fire the coil instead of the old points and condenser. On saws we are dealing with magneto electronic systems. There are several different types of electronic ignitions(And manufacturers own brand names)-Electronic(Generally all types),Digital,Transistorised,and CDI-Capacitor Discharge Ignition. Sometimes any type of electronic ignition are mistakenly referred to as CDI,CDI is usually a larger bulkier more complicated system with very high power output where basically the magneto charges a capacitor which can release up to 400 volts(Instead of 6-12 volts) into the primary windings of the coil resulting in a very powerful spark. A good example of a CDI system is the Mercury "Thunderbolt" ignition,the factory spark tester has a 1 inch(!)gap,which it will easily fire with a fat blue spark! In the automotive aftermarket one can buy a powerful CDI box such as the MSD brand which is a CDI type and popular with racers.
I don't know of any saws that use CDI type as it's just too big and bulky. Most seem to be a basic magneto/coil type with an electronic trigger.
It's too bad saw ignitions are a moulded 1-piece unit as it doesn't allow us to add any aftermarket high output accessories like electronic boxes and coils...
The race type spark plugs(Platinum etc.) take less voltage to fire so they allow more voltage across the plug gap,one of the few tricks left to us to improve a saw's ignition power...

 

[duramax99]

trapper mike Just curious but what ngk plug do you like to use? ive found bpm7y's but havnt had luck finding anything better yet.

 

[trappermike]

Your choice of BpM7Y plug sounds good,I think it's ok for stock or mildly modded saw. "7" is a good heat range for that,I would try an "8" heat range for hotter saws. The "P" denotes an extended tip which is good for general use,For modified or hard running saws I don't use the "P" type,it's a little risky to run an extended tip near the piston in a hotter motor.So for extended tip you have BPM7 or BPM8 types,and BM7 and BM8 types for non-extended tip.
I'm waiting for an NGK catalog,but I haven't found a platinum or Iridium type plug from NGK for the short 3/8" reach plugs yet, but the 1/2" reach plugs can be used with a 1/8" spacer or 1 or 2 extra washers under them,they are longer porcelain but in many cases will fit in the stock location. If you can make these fit for you then you really now have performance NGK plugs to work for you,the racing types are B8HV and B7HV,they are not very expensive. These are high quality plugs made for performance motors and work very well.
In Bosch plugs I use WS5F-extended,or WS5E standard tip.
I'm going to search the new Bosch and NGK catalogs for the performance type plugs in 3/8" reach again to see if anything new is available...

 

[duramax99]

Thanks a ton, i ordered some bm7's. I see your from B.C as well im in the interior.

 

[Stihlmech]

hello all, im new to the forum but definately not to modding saws. i have an 038 that i have highly modded and have the time to test things. on my saw, i have advanced the timing 5/16" on the outside diameter of the flywheel. it gave me another 1500 rpm in the cut. i have played around with it a little and that was the best i got. all i did was remove the key, and advance it. it is not needed, just make sure that the crank and the flywheel do not have any grease or anything else on it when you install it back on.