Converting the Stihl 031AV to electronic ignition

[desr580]

Hi guys sorry if this sounds stupid but I have stihl 031av and it still has points in it I have checked coil with a multi metre and it's fine when I compare it to the manual can anyone tell me what I need to do away with points thanks

 

[RayJohns]

I just completed this conversion on my Dad's Stihl 031AV, which originally had breaker points. Let me see if I can give a decent rundown on what's required, in case anyone in the future comes along needing info:

So, first things first..

If I'm not mistaken, the 031AV was produced in two versions - one which used breaker points and another which used some sort of electronic ignition plate or something - both are shown in the service manual, as well as the parts diagram. My Dad's saw (purchased in 1980) had the breaker points w/ capacitor (aka condenser), so that's what I'll cover here. It also had the flywheel with one magnet on it, marked N and S (for North and South).

This project all started when my 90 year old father called me up and said he was having some trouble starting his chainsaw. Okay, no problem I thought; I told him to bring it over and I'd help him fire it up. It had been sitting for nearly 5 years, so I figured it probably just needed a little adjustment and/or cleaning. Ha.. wrong.

So he brings the saw over and we attempt to fire it up. Pull after pull and nothing. I reset the fuel mixture screws back to the stock setting, put a fresh sparkplug in, etc, etc. - nothing much helped. We were only able to get it to fire up once or twice for a brief moment and then it cut back out. What the heck? I had never had so much trouble getting a saw to run. The more time I spent, the more I started to realize something just wasn't right here...

So I ask my father, "Hey Dad, have you done anything to this saw?"

Dad: "You know.. now that you mention it, I think I did take it all apart once and do something to it, but I can't remember what I did"

Me: Sinking feeling as I started to recall dropping by his house one time and seeing him with his chainsaw all apart on the work bench. I started to vaguely remember that, sure enough, he had taken the saw all apart once for some unknown reason. The more I started to think about it, the more it all started to come back to me: yes, the saw had stopped working and I remember he had said it didn't look good and he might have to take it "really far apart" to fix it. He told me he was worried he might be in over his head, but didn't wanna pay to have the local dealer repair it. He told me he remembered drawing some pictures of the parts of the saw on some cardboard and that he had poked holes where all the screws were located as he took everything apart. Yeah.. now it was starting to all add up.

My Dad is pretty handy with some stuff, but as Clint Eastwood likes to say: 'A man's got to know his limitations'.

I figured my Dad had probably gotten in over his head on this one and that maybe the result was a saw that never really ran quite right after that. So I told my Dad to head on back home and I'd see what I could figure out when I had a minute. What started out as "just a quick look at his saw", quickly turned into a two week expedition into converting the 031AV from breaker points to electronic ignition. Before I knew it, his saw was in parts all over my garage floor.

HE WASN'T EVEN OUT OF SIGHT AND I HAD THE SAW APART!



After taking his saw apart, I discovered what he had attempted to repair: the high tension coil wire had come out of the coil and he had put it back on with bailing wire and some duct tape. It didn't seem like a half bad repair, actually, but I suspected there was probably more wrong some place. I decided that most likely the breaker points were burnt and/or out of adjustment. Since I wasn't really in the mood to fiddle around with setting breaker points, I decided, "how hard could it be to convert his saw over to electronic ignition?"

I called my Dad and jogged his memory...

Me: "So I discovered the coil wire on your saw had come loose and you repaired it with some bailing wire and Duct tape..."

Dad: "Oh.. okay, yeah, that sounds right; I remember that now...". He continued, "the saw ran fine after that, so I don't think that's the problem"

Me: "Yeah, no, it looked okay to me also - your Duct tape job was holding the coil wire on just fine; I think something else might be wrong also, so I'm going to just convert your saw over to electronic ignition like the newer ones. I think this will make it run a lot better and start much easier for you."

A+ FOR EFFECTIVE USE OF DUCT TAPE:



Dad: "Oh, that's great! Yeah, I nearly wore myself out trying to start it last week. I had to come in the house and sit down after pulling the cord so many times, when I couldn't get it to start".

So that was that: I was on the hook to convert this thing to electronic ignition.

I have to say, it's been quite a while since I had heard such excitement in my father's voice. I'm not even sure the birth of my two children caused him to sound so joyful. I told him to give me a couple of weeks and I'd touch base with him and let him know how it was going.

Dad: "Okay, that sounds great - I'll wait to hear from you".

So, the first thing I did was search on google and actually ended up arriving at this very thread right here (as well as a few others on the forum). After a bit of reading, I was more confused than when I started. I wasn't sure if it would be best to use a generic Oregon module or maybe try to find the flywheel and ignition plate from another 031AV that came with electronic ignition or what.. maybe try to adapt some parts from a Stihl 032 or something??

In the end, I decided maybe it was best to back up and educate myself on electronic ignitions in general - which is what I did. After some reading, I decided that most likely Stihl was using some sort of Hall Effect sensor, which sensed the magnets in the flywheel going by and this in turn triggered the spark plug. That assumption ultimately turned out to be incorrect, but initially I figured that was probably the method Stihl was using. I also read (on this forum) that just slapping on an electronic ignition (generic or otherwise) onto the 031AV could cause the exhaust to glow red during operation - gulp, that didn't sound too good. I wasn't sure why that might happen, but I could just picture my Dad burning his house down and the fire department tracing all this back to me and my "upgrade" on his saw. Haha. Dad always took pretty good care of us kids, so I figured I better make sure I got this job done right.

continued below...

 

[RayJohns]

After further reading on-line, I turned to the Stihl factory service manual for the 031AV saw, which I had previously downloaded for my Dad I guess. I found it on my computer and read through the section on timing the electronic ignition. It looked pretty straightforward, so I decided I would just order some parts and see what arrived. Not my normal M.O., but I thought I could probably figure things out along the way, after seeing some of these parts in person. I decided that - worst case - I could just build my own electronic ignition module using IC's and a breadboard and then work backwards from there. I was still thinking the Stihl's electronic ignition trigger worked off the Hall Effect, although - as mentioned - in the end, this proved to be incorrect.

While researching electronic ignitions, I noticed a lot of people talking about the Oregon electronic ignition triggers (which looked to be sort of a generic item, that was maybe intended to work with a wider variety of ignition systems). I even found one guy on YouTube who had taken the electronic ignition out of a chainsaw and modified it to get his antique 1940's motorcycle running. If this guy could accomplish that, I could fix my Dad's saw!



Okay, so what I finally decided to buy was the Stihl Ignition Trigger Switch - part #1118 400 1001 - which I purchased off ebay.



I also ordered up a new coil, but in the end, I didn't end up using it. Now I should interject here that this modification required a fair amount of work to pull off, not to mention some tools and a bit of background knowledge with 2 stroke motors, etc. I'm not saying the average backyard mechanic can't do this upgrade (you certainly can), but just be aware that you may need more than just a screw driver. In fact, you're probably going to need a flywheel puller (M22 x 1.5) as well as a timing light - just to name a few things. Oh, and a dial indicator also will probably be needed.

Okay, so the flywheel sure didn't wanna come off the saw. My lathe was out of commission, so instead of making a puller, I ended up just ordering a flywheel puller kit. I bought mine off amazon here:

http://www.amazon.com/gp/product/B004MB13D6/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

Great kit and very high quality. The 22mm x 1.5mm puller allowed me to pop the flywheel off the crank in short order. I did away with the points and capacitor and cleaned up the saw while waiting for the trigger switch to arrive in the mail.

BEFORE:



AND AFTER:



When the Stihl ignition trigger switch arrived, I wired things up to see how it all functioned. The trigger switch grounds to the saw's housing and then has one lead that attaches with a small screw. This lead goes from the coil to the trigger and then onto the ignition on/off switch (which is used to turn the saw on/off). So basically the on/off switch on the back of your saw grounds out the ignition trigger switch circuit. When the switch is in the down (off) position, the coil is effectively grounding out and bypassing the spark plug. When the switch is in the up (on) position, the energy from the coil is allowed to discharge via the spark plug.

The generic ignition switch modules (such as those available on Amazon or from Oregon) have both a positive and negative grounding lead, while the Stihl part #1118 400 1001 has just one. I'll include some photos of the wiring, but it's pretty straight forward. You will need to find yourself an M3 screw to attach the lead and that's basically it for the wiring harness.





Okay, so why can't you just bolt everything up and have it work? Well, there is a problem... and this is probably why people discover their exhaust glows red when they just bolting an ignition trigger switch onto the 031AV saw.

Continued below...

 

[RayJohns]

Turns out, the stock timing of the 031AV saw isn't exactly compatible with when/where the Stihl #1118 400 1001 trigger fires the spark plug. Remember I mentioned (above) that I figured the electronic ignition trigger switch worked off the Hall Effect (where it senses the proximity of the magnets on the flywheel going past it)? Turns out, that's not how it works, after all. In fact, when you wire Stihl's ignition trigger switch up to the 031AV saw, it doesn't pay any attention to where the magnets on the flywheel are. Matter of fact, you can have the trigger switch clear across the room (given a long enough wire) and it will still happily fire the coil for you.

So I emailed the engineer I know at Stihl and I asked him about this. He said my assertion was correct - that the trigger switch worked off the coil's voltage, not the magnets in the flywheel, per se.

So what's the problem then? It fires the coil right?

Well, yes, but there's another problem. While the trigger switch will fire the coil just fine, it fires it at the wrong time. Due to the location of the magnet on the flywheel, "firing voltage" in the coil is reached when the piston is not in the proper location in the cylinder. I didn't make exact notes regarding the specific piston location, but as I remember, it's probably firing too soon - and I'm guessing this is what is causing people's exhausts to glow red also. In other words, the spark is probably going off before the piston has moved far enough to close off the exhaust port in the cylinder.

Remember, this is a 2-stroke motor, not a four stroke. That means there is no mechanical valve to seal off the exhaust port. Only the position of the piston itself opens or closes access between the exhaust system and the combustion chamber of the motor - so if you have a spark that is occurring while the exhaust port is still partially exposed, then what you have done is effectively incorporated the exhaust chamber into the combustion chamber. Due to the somewhat rudimentary nature of a 2-stroke motor, this probably won't keep your saw from firing; however, it will negatively affect its performance, not to mention heating up the exhaust manifold.

So, when is the saw supposed to fire then? Well, according to the service manual, the spark plug is supposed to fire when the piston is 2.7mm BTDC (before top dead center). Normally, on a race motor or something of that sort, engine timing is expressed in degrees of rotation of the crankshaft prior to the piston reaching top dead center (TDC) on the compression stroke in the cylinder. In simple terms, the spark plug needs a tiny head start when it comes to exploding the compressed air/fuel mixture inside the chamber, so that the optimal explosion occurs in such a way as to thrust the piston down in the chamber.

On your chainsaw, if you remove the spark plug and stick a dial indicator into the spark plug hole (or a Popsicle stick for that matter), you can readily determine when the piston has reached exactly TDC. With a popsicle stick, the stick just moves up and down; with a dial indicator, a needle sweeps back and forth. On my particular dial indicator, it's read in thousands of an inch, so I had to convert the desired 2.7mm to inches (which works out to about .106" before TDC). So there you have it: we want the spark plug to fire when the piston is .106 inches from reaching the top of its stroke in the cylinder.

TIMING THE SAW:



On my Dad's saw, if you move the piston to exactly TDC, you'll notice there is a little line on the flywheel, which matches up to a center-punched hole on the saw's flywheel housing. It's very tiny, but it's there - a factory TDC mark. There's also a timing mark cut on the edge of the housing's mating surface, but this reference is for the mechanical breaker points, not any sort of electronic ignition trigger switch.

Okay, so at this point, if you just wire up the Stihl electronic ignition trigger switch, you'll find the saw fires at the wrong time. To compensate for this, you basically have to re-time the saw yourself. To do this, you use a dial indicator and rotate the piston to exactly .106" before TDC - then make a reference mark adjacent to the timing mark which is already on the flywheel. This is where we want the spark plug to fire (i.e. 2.7mm before the piston is at top dead center). Now, at this stage, if you put a timing light on the saw (and crank it over manually using a drill to turn the flywheel retaining nut), you'll see that the ignition fires at the wrong time. It doesn't fire when the piston is 2.7mm before TDC; instead it fires about 30 degrees too early.

HERE YOU CAN SEE MY HOME-MADE TIMING MARKS:



So how do you correct all this?

Well, under normal circumstances, you'd simply adjust the distributor. But, of course, the Sthil doesn't have one. So the only means of adjustment the timing - so that the coil fires when the piston is 2.7mm before TDC - is to physically rotate the flywheel relative to the crankshaft & piston. This serves to adjust the timing of when the magnet on the flywheel goes past the magneto / coil - thus altering when the spark plug fires.

Now, I should point out here: I did read that some 031AV flywheels have different configurations on the magnets. Mine had one magnet, marked with an "N" and "S" for North and South. If your flywheel has something different, then be careful, as this could throw things off, I would imagine.

FLYWHEEL WITH "N" & "S" MARKS BY MAGNET:



Okay, so all that is needed is to turn the flywheel a bit, so the saw fires at the correct time. Now the problem with this, as you might have already guessed, is that the nose of the crankshaft has a woodruff key installed in it, which indexes into a keyway on the flywheel. This means the flywheel can only be installed one way. Luckily, however, the flywheel also has a taper, which holds things rather securely in place. This is the same sort of taper used with a chuck on a drill press (and in my humble opinion), it's more than adequate to hold the flywheel in place on the crank [when retained by a nut]. Of course, you'll need to remove the woodruff key - which is easier said than done. In my case, I found that using a little power center punch worked pretty well. Initially, I punched a few times on the face/end of the key, until it started to lift up in the channel. After that, I hammered it a little, to move it further, until I was able to use locking pliers to remove it completely.

With the indexing key out of the mix, you can place the flywheel on the nose of the crankshaft however you want; the taper holds everything fine, especially with the nut in place. At this point, I simply made a few timing marks and verified that the spark plug was firing when the piston was 2.7mm before top dead center, using a timing light that I had handy. Once all this is done, simply tighten down the nut on the flywheel and away you go (don't forget to gap the flywheel edge about .010" away from the coil - see the service manual for specifics).

Well, almost done...

You'll need some way to hold the ignition trigger switch onto the coil. There is a part # from Stihl for this - part # 1113 405 1901 - but I was unable to find it. Instead, I used an old stainless steel knife blade, which I found in the garage, and fashioned a mounting bracket from that. I then riveted the ignition trigger switch onto it and finally wired everything together into the wiring harness.

MY D.I.Y. BRACKET MOUNTED TO THE COIL:



Worked like a charm!

So that's basically the deal. You can convert the 031AV using Stihl's own electronic ignition trigger switch module, but you will have to re-time the saw so that everything fires at the correct time; and this requires moving the flywheel on the crankshaft maybe 30 or so degrees (roughly). It's not difficult, once you understand everything that is required and why, but it does involve the use of a dial indicator and timing light, as well as adjustment of the flywheel relative to the crankshaft & piston.

Hopefully my run down here provides some helpful information. I'll see if I can upload a few pictures I took along the way, as well as a video showing test firing of the final result.

HERE'S A VIDEO TEST FIRING THE SAW (I FORGOT TO PUT THE CHOKE ON INITIALLY, OOPS!)

 

[jener8tionx]

I know this is an old post, but great information. I would just like to point out that the 031 is supposed to fire at 2.5mm BTC on a breaker-less ignition. 2.7mm is for the 032.

 

[PogoInTheWoods]

May be old, but the best post I've found so far on the subject. However, it seems as though there is some confusion about whether the 30 degree adjustment of the flywheel to obtain the correct timing is by advancing it or retarding it. Everything I've read indicates an advance (counterclockwise) adjustment is required, though the previous post suggests the stock timing is already 30 degrees (or so) too far advanced and requires appropriate correction which would mean rotating it clockwise to retard it. Am I missing something, or is the author just confused about the direction of the flywheel's rotation?

 

[trappermike]

Number #1,is an 031 worth all the time and money and frustration. #2 it was hard to fit an aftermarket ignition and still get the fuel tank on,space was minimum. #3 half the time no mods worked, the 031 would just misfire horribly no matter what you did to it... If you succeed great for you!
The real problem was called "Edge gap',not referring to the gap between coil and flywheel magnet,but the exact position of the flywheel magnet compared to the coil,if it was too early or too late a real weak spark causing misfiring resulted. In points models I used to try varying the point gap to either narrow-.012" or wide .018",this would sometimes cause edge gap to be correct and they would run ok,didn't always work but best shot you have.
On some electronic modules like the Atom,you could reverse the wires as suggested and they would run.