Stihl 056 bosch ignition

[blind hog]

Recently solved my Stihl 056 Bosch ignition problem. After visiting this and other websites looking for answers to the "it runs for about 20 minutes and then dies" problem, I discovered many people having the same issue. My saw finally quit firing at all. I'm sure someone has already posted this solution but i haven't seen it. It's fairly obvious that the bottom (detachable) portion of the ignition unit is the coil. Cut the jumper wire from the coil to the (epoxy filled) electronics, solder this lead to a 1118-400-1001 trigger unit lead (26.00 from stihl dealer), ground the module, and the ignition will fire, assuming that the coil itself is not the issue but rather the electronics. Strangely enough the saw still would not fire. Blaming the lack of combustion on ignition timing, I pulled the key out of the crankshaft and began rotating the flywheel a few degrees in either direction. Retarding the flywheel (clockwise) about half a keyway created the desired response. I undoubtedly need to fine tune the ignition timing, but the saw runs perfectly. I then removed the top (detachable) bosch trigger unit and bandsawed off the (epoxy filled) electronics in order to mount the new trigger unit properly.

 

[blind hog]

Correction, advanced flywheel (counterclockwise) half a key.

 

[hotshot]

Great idea, do you have any pictures?

That's a great idea, did you take any photos along the way?

You can now mark the top dead center position on the case & flywheel, print a degree wheel from one the many old timing posts on the site, then mark the case again at 26 BTDC. Hook an automotive timing light up to a 12 VDC battery & use the induction pick up from the plug wire then run the saw and see how close to design the timing is.

The voltage "trigger" to the new chip must be delayed in sensing the coil's change of induced voltage to determining when to fire, since you had to advance the flywheel? The original trigger unit is at the top of the Bosch module like you had stated, about 180° out from the coil on this model.

 

[Trigger-Time]

I do think you can get one set to close to TDC.
It may run it's best set that way but may burn a hole
in top of piston in time.

Doesn't the plate the coil mounts on adjust for timming
without needed to move flywheel.


TT

 

[maico490]

056 ignition systems were one of the few things I thought I knew something about but what you've done makes me think I still know nothing. Please can you get some pics up ( else it didn't happen ) so we can all see what the fix is. I'm guessing that because of the mutiple magnets in the Bosch flywheel the ignition could be firing several times per revolution. This wouldn't neccessarily be a problem as modern ignition units will support very high revs and most small 4-strokes fire every rev as they get their trigger from the crank. Also agree with Trigger-Time about there being quite a bit of adjustment on the backplate.

 

[blind hog]

I'm glad you mentioned 26 btdc, the preferred ignition timing was my next question! The reason I rotated the flywheel instead of adjusting the backplate was because I didn't know how much adjustment would be needed. I started by making big changes. after finding where the saw would run I did try adjusting the ignition plate. I adjusted to nearly full advance but the saw would not fire there. It is certainly possible that I just didn't go far enough. Yes I did take pictures, but I am computer challenged so I will have the wife help me put them on after dinner. I did run the saw today for about two hours; it ran great.

 

[sefh3]

I want to see pics of this. Read my signature line and it will help you with the pictures.

 

[blind hog]

Picture

Here's a picture.

 

[blind hog]

I guess I should have taken more pictures, but it seemed like a futile attempt until I got spark. I only have two pictures and they're both pretty much identical. As you can see it is VERY simple. I ordered a new module for it today, the module you see in the picture is in very rough shape. Since it works so well I don't mind spending 26.00 on it. If anyone would like I can take more pictures at that time. Let there be no doubt, this DOES WORK. Try it.

 

[mountainlake]

Good going, I have a friend with the same problem. Steve

 

[hotshot]

Great Idea!

Don't know why it would not make spark at any position, that part of your great experiment does'nt make sense. The magnets in the FW don't know where the coil is rotationally, just that it passes by to charge it. The trigger you installed then collapses it to fire the secondary side.

There is less than +/- 3° adjustment, or 6° total on that Bosch CD baseplate.

Sure would like to see it degreed while running, do you have an automotive timing light or need information on how to do it? I can tell you how to do it from the PTO side with the clutch carrier marked as reference, as doing it from the FW side is not "OSHA" approved (yanking the starter off while it's running) and keeping your fingers away from the spinning fins. Just takes a few seconds to shoot the marks while it's running about 6,00 RPM.

Probably have thrown a half dozen of those dam things in the trash....now I may be sorry. Same thing for the SEMs.

 

[Trigger-Time]

Here's a picture.

Thanks for the Picture, this is my weak point when it comes
to chainsaw repair. I have 056 Super I put points in and a 056
thats waiting on a SEM FW and coil I picked up. But I think
I may try your repair on the Bosh setup and save the SEM
in case I ever find 056mag II

This fix could make for some happy 056 owners


Thanks,
TT

 

[blind hog]

Yes hotshot, I do have a timing light. Thanks for the suggestions, but I think I,ll do the timing from the suiside. I'll remove the starter and fanwheel first and start it with a good cordless drill (after marking the flywheel). I did hook a digitron tach to it today. To my disbelief it displayed an idle rpm of about 2000 and high end of about 9400. I then hooked the tach to my 051 and showed about the same readings. This leads me to believe that it's just firing once every two cycles! Like maico490 said, looking at the flywheel you would think it would fire several times (I expected 4 times every two cycles). I'll do more research. Oh yeh I took pictures of the tachometer event if anybody wants to see them.

 

[hotshot]

Sounds fine

Once per cycle sounds fine, as there's only one North magnet in the #0204 098 002 Bosch CDI flywheel, the other three are South. I'd like to know the approximate flywheel keyway to shaft key orientation when I come across the next dead Bosch.

 

[NeoTree]

The 056 should turn 11,000 RPMs
056 Super - 11,500 RPMs
056 Mag II - 12,000 RPMs if memory serves me right
Average Idle speed should be 1,800 w/clutch engaging at 2,500
advance is adjustable from 26.2 to 27.5 degrees BTDC

My weakspot is ignition knowledge as well, so this will only work on the non-SEM equipped saws? I'm just waiting for the day my mag2's to stop. I absolutely love them big suckers. Running a ported one ain't bad either:hmm3grin2orange:

ps. Awesome info blind hog, you deserve mucho rep

 

[sachsmo]

Rekon this would work on an old Sachs Dolmar with the Bosch ignition?

 

[maico490]

I've been away for a day or two so haven't kept up with this thread. All I can say is hats off to you blind hog. Even Lakeside said that modules won't work on a Bosch flywheel because of the 4 poles. From your rpm readings the module must be ignoring the 3 souths and only firing when the north pole passes which I suppose must have been what the Bosch electronics were doing originally. Maybe the aftermarket modules like the Nova and Atom don't differentiate between the poles.
I nearly threw out my Bosch flywheel and module the other day but it will be awaiting another 056 now.

 

[blind hog]

I'd have to say that ignition is my week-point as well. I understand how the coil operates or at least the theory, but that module is full of fairy dust as far as I can tell. Most of the ignitions I have dealt with are either points or magnetic trigger. The way I fix the points ignitions is to install one of these modules. Its normally pretty simple, if the magneto is bad you just replace it. That wasn't an option here. I really didn't think this would work because of the flywheel design, but I thought it might lead me towards something that would work. Seems odd that it would ignore the south magnets and recognize only the north, but I'm not disappointed. I'm not familiar with the Sem ignition, the bosch ignition is modular so it was easy to isolate the coil. That Sachs coil certainly looks identical. As far as the flywheel indexing is concerned I'm going to slap a degree wheel on the pto side and find out just how many degrees I have advanced the flywheel. Right now I think the ignition timing is a hair slow. The saw never offers to tear your hand off like it occasionally use to. also the head temp stays pretty cool (maybe I should leave it alone) as I also had an under plug censor on it.

 

[Justsaws]

Mega-Fire modules will work. I would recommend that the module be mount up near the rear handle instead of under the flywheel as they can be a tad temperamental with heat.

I have yet to find a Bosch coil that they will not work with.

It is a good solution to the ignition issues with the 1115 Stihls.

Lots of Bosch flywheels for the Mags.

The SEM modules can be done just more of PITA.

 

[blind hog]

Good idea justsaws. I'll run a lead out with the plug-wire. Also makes it more serviceable.