Stihl 661 conversion from M-tronic to non M-tronic (unlimited)

[blacksmith]

First off I would like to thank @Redfin for this info he's the one that came up with this mod that he did for another fella on this site.

I have a 661 that was giving me lots of issues, it spent a lot of time at the shop under warranty. Many new solenoids, wiring, carb and a complete new M-tronics system all together twice over. Still wasn't working right.
I just wanted to be done with the autotune crap. Don't get me wrong when it ran it ran really good but was not reliable.

So with the help of John through texts and talking I stumbled my way through this mod and I couldn't be happier now with my 661!

All that I ask is that if everyone can please hold any posts until after I post all of the info s it is continuous. I'll put a post at the end letting everyone know when I post the last bit of info.

Thank you in advance for being patient, there is a lot for me to post!

 

[blacksmith]

These are a list of tool that you'll need. Volt/ohm meter and a 1/4" socket set.


5 in 1 screwdriver, scwrench and a 4 " grinder with a flap disk.

Dremel tool mine is a craftsman. The hand piece attachment makes it a lot easier.

Carbide cutter.

Wire strippers, needle nose pliers and wire crimpers.

 

[blacksmith]

A feeler gauge with a thickness of .008.

 

[blacksmith]

Material needed is. 1122 (066/660) coil and flywheel, Walbro WJ-69 carb, an 18" piece of ignition wire, dielecrtic grease for the coil wire, 12" piece of #20 AWG wire, small blade sta-con red insulated connector and a small red insulated butt connector

 

[blacksmith]

First things first remove the flywheel, coil, carb and all M-tronic wiring and wiring harness. Separate the wiring harness. Unplug the wiring harness from the coil. Cut the black wire off as close to the plug that was plugged into the coil. The terminal on the end of the black wire needs to be reused for the stop switch circuit.



Butt splice the lenght of black #20 AWG wire using the red insulated butt splice to the black wire that you just cut from the plug harness as stated above.

It will lool like this. Although my butt splice is closer than I wanted it because I screwed up but it still worked out.


The green wire with the yellow stripe that was in the wiring harness will be reused as it was before. This is the one that is attached to the case with a screw at one end (by the coil) and the other end is the other side of the off switch. Route the wire in the carb box as shown in the picture below. And bring them out in the coil area.



Now install the WJ-69 carb.



All mods to the carb area are done.

☆Just a side note if you push the lever too far for the choke it can flip past the choke rod on the carb! If your easy with it there will be no problems. You may need to mod the lever or carb choke rod.

 

[blacksmith]

Next using the grinder with the 4" flap disk remover all the plastic from the back of the flywheel. Use caution not to get the flywheel too hot because heat can cause the laminations to separate. Just take your time.

When you are done the back side of the flywheel will lool like this.



Now first test the coil to make sure that it is good before you mod it! I learned because I had a new OEM coil that I modded and it no way shape or form could have messed anything up. Well lets just say I stuggled as to why I wasn't getting any spark and was scratching my head. I ordered a $20 coil and checked it before I modded it. The readings were way different. So my conclusion is that my OEM was bad internally and could not be returned because I modded it. Sorry for the rant lesson learned.

You are going to take two different readings. One from the spade terminal on the coil to the coil mounting frame itself.




And one from the spade connector on the coil to the end of the spark plug wire.

 

[blacksmith]

Next is probably the hardest part, modifying the coil.

Using the dremel tool with the carbide bit. Start slowly shaving the outer part of the coil case off to allow for a better fit. This coil as you can see is a lot thicker than the M-tronic one. Be very careful not to go too deep and get into the windings of the coil because it can ruin it.




Now use the grinder with the 4" flap disk to shape the back side of the mounting hole so it will properly fit in the case. In the picture below just above the mounting hole to the left will need a pocket ground out with the dremel tool and the carbide bit, this is going to be your new mounting hole. Well kind of.


Another shot of pocket to be ground out for the new mounting hole.

 

[blacksmith]

FYI the coil in the post above is the $20 coil. It has a slightly different shape, you don't have to get too aggressive with shaving the outside and it fits in the case a little bit better.

Now it's time to shave the case with the dereml tool using the carbide bit. Be careful not to take too much out where you pop through the other side. As you can see in these two pictures I punched a very small hole but it wouldn't effect anything. Again just take your time.

 

[blacksmith]

Now the next step is installing the coil and flywheel. Once your coil fits properly in your saw case now fit the flywheel to the crank.

You may or may not need to put shims under your coil. I did not but other guy's needed to. The shim may be two washers under each end or an oversized nut that will slide over the 4mm screw.

You can get longer 4mm bolts at Lowe's.



I put two washers on each bolt.



Check the coil to case fit you may still need to tweak the coil to get it to fit.






As you can see the coil that is in my saw now is a $20 aftermarket, it actually fits a little better (it's a little thinner) and I didn't need to put any shims under it. I did however tap out the coil mounting holes to 5mm.

 

[blacksmith]

So here's the last piece of the puzzle. Mounting the flywheel.

This is the picture of the flywheel/ coil position while the piston is top dead center!







After your flywheel is set and tightened down. Loosen the coil and set the gap. Now you're done and ready to rock.



One last note that I want to say is that the key does not line up! I did not cut a new key way in my flywheel so there is no key in mine. I've run it hard and have had no problem yet.

 

[blacksmith]

Well everything is posted up, feel free to ask any questions on something that I may not have explained well enough!

Thank you for your patience and John @Redfin thanks for all of your help!

 

[blacksmith]

Sorry guy's I just got word that none of my pictures showed up. It's probably because they wer pasted from a PM and not uploaded. Soooooo Iam gonna work on getting the pictures up. That sucks because I can see the pictures if Iam logged in but I can't see the if Iam not!

 

[blacksmith]

Let me know if I am on the right track. I attached 6 pictures between the first two posts are the pictures full size or are they small? These pictures are taking forever to load and I have 28 to post!

When I am logged in they are full size but wen I log out and look at them as a non member they are small.

 

[huskihl]

Let me know if I am on the right track. I attached 6 pictures between the first two posts are the pictures full size or are they small? These pictures are taking forever to load and I have 28 to post!

When I am logged in they are full size but wen I log out and look at them as a non member they are small.

The ones you reposted are perfect

 

[blacksmith]

The ones you reposted are perfect

Cool thanks for the update. More on the way if it cooperates I may have to finish it up tomorrow.

 

[KS Plainsman]

I'll second it. I can see all the tool pictures, down to the feeler gauge.

 

[blacksmith]

I'll second it. I can see all the tool pictures, down to the feeler gauge.

Working on it, I have to delete the pictures that I can see and repost them all. Glad to see that it's working now!

 

[KS Plainsman]

Working on it, I have to delete the pictures that I can see and repost them all. Glad to see that it's working now!

I appreciate your effort Sir! Thank you!

 

[blacksmith]

I appreciate your effort Sir! Thank you!

Not a problem, if this thread helps to relieve some one of there problem child 661 and turns it into a tunable animal then that's all that matters!

 

[blacksmith]

Well it looks to be that I've successfully uploaded, keep me posted if there's any issues or questions!