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Sachs Dolmar Ignition Woes


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  #1  
Old 03-14-2016, 10:49:13 PM
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Default Sachs Dolmar Ignition Woes

I have this big honkin early 1980's saw that suffers from no longer available itis.

A Dolmar 153 (actually a Poulan 6000) which is a 100cc unit that with the 36 inch bar wili easily go through anything for a while. After it heats up it won't re start as the ignition is wonky. This is a trait of these Bosch solid state units as they age.

Does anyone have an ignition unit? Or the savvy to dive into this potted assembly? This ignition is also supposedly on: Husqvarna 480, 285, 2100. Stihl 045 & 056 and some 041 models. Dolmar 119, 120 and other Dolmars.
The coil is new as it's a current production coil.

Pic for familiarity.
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  #2  
Old 03-14-2016, 11:56:00 PM
bigGURN bigGURN is offline
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Default Re: Sachs Dolmar ignition woes

Awhile back, I ran into this problem with my own Dolmar 133, I have since fixed piles of saws with this ignition, this was a pretty common occurrence with the Bosch 2 piece ignition. For most of the saws with this igntion the historical fix is to locate and install an appropriate SEM type GA ignition/coil and flywheel. While this works, it cost quite a bit of money. Further, much like a functioning Bosch ignition, they can be hard to locate.

With this information I decided that because my ignition was already broken, I could not make it any worse

The Bosch ignition is made up of the coil and the over complicated electronic "trigger" that triggers the coil to release a spark. On the Bosch unit the trigger is made up of the module and a pick up for the module. This means that the flywheel actually has four poles to make the whole system work. One north pole and three south pole magnets. This creates a magnetic field that first excites the coil then the trigger module so that it can then trigger the coil (which was previously excited)... Very complicated. In the picture below, the portions outlined are the trigger module and the pickup for that module:


I decided that since the trigger module & pickup must be the issue that I should start by removing them from the saw (coils themselves rarely go bad). Therefore, I removed the coil from the backer plate and then removed the backer plate with the attached pickup & module from the saw. I cut the wire to the pickup and removed it. With that done, it was time for surgery... I used the hacksaw to cut the trigger module off (I should have used the bandsaw), leaving me with two "extra" pieces (the black wire went to the kill switch):




I then used the grinder and a paddle disk to clean and square up my hacksaw job, then I installed the backer plate back into the saw and re-installed the coil:

Last edited by bigGURN; 03-15-2016 at 12:08:32 AM.
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Old 03-15-2016, 12:03:53 AM
bigGURN bigGURN is offline
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Default Re: Sachs Dolmar ignition woes

With that done, it was time to address the issue of the trigger module & pickup... I determined (before I started) this could be simplified by replacing the entire assembly with a Nova II ignition module (normally used to replace the points and condensor in an older ignition system). The module requires no pickup and is much more compact. Further, one can be purchased for under $15 USD, making it a much more affordable option over the SEM GA option. To wire the NOVA II module, I soldered the (+) lead to the input lead from the coil and then the negative lead goes to ground (its convenient to just run the wire to the mounting screw for the module). The nice thing is the module can easily be mounted to the backer plate, keeping everything contained under the flywheel.


From here I reassembled the whole thing and found I had spark! But a weak spark then it occurred to me that the spark also seemed out of time. This made sense since the original system first charged the coil then used the pickup to excite the module to trigger the coil to release the spark... the solution with the Nova II mod... advance the timing all the way. With this done, I had bright white spark and the saw started on the 2nd pull!

I then pulled the saw back down and added a wire for the kill switch. I did this by making a pig tail harness that plugged into the (+) side of the Nova II module with one lead plugging into the coil lead and the other routed up to the factory kill switch. This grounds the coil when in the off position. After this was done, I reassembled the saw and after sitting a few hours the saw started on the first pull.

I have also found that Stihl produces their own module that is a one wire module (it is self grounding) they are quite a bit more money (~$30 USD) they would simplify the process by removing the ground wire. The Stihl part number is 1118 400 1001.

One final note, I have had an issue in the past with modules getting too hot and then not working, this has usually been on a saw or piece of equipment where I replaced the points. If this happens, the module needs to be relocated to a cooler location. In this case one could plan to relocate the module up into the chassis near the kill switch as this would be the coolest part of the saw "under cover." This will be easy enough as one could just solder the kill wire to the coil and splice the kill wire up near the kill switch. However, in the past when the heat issue has arisen it was because the module was close to the cylinder (the hottest part of an engine). Thus far I have yet to have an issue with the module under the flywheel.

As mentioned above, I have gone on to do this modification on several other saws, just last week I modified a Stihl, I removed the trigger, but left the electronics in place as they did not interfere with my mounting. Same wiring as previously, but this time no timing advance, the saw was happy to run wit the timing in the stock position, something I have found that varies between saws.

The stihl:



The Dolmar 133:


My Poulan s6000


The stihl running:


Good luck, I hope this gets you running again!

Last edited by bigGURN; 03-15-2016 at 12:15:57 AM.
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Old 03-15-2016, 08:32:39 AM
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Default Re: Sachs Dolmar ignition woes

Thanks so much for your reply. I was surfing for answers until 2am last night and came across your posts elsewhere on the web. The Nova looks like a cheap solution. But, I worry about timing as I don't see how it is energized.
Don't want to stick it or ventilate the piston.

I did run across this in my surfings.
http://www.ebay.de/itm/Zuendung-erse...-/321366822778

** Per the ad: This ignition is only compatible as a replacement of fully electronic Bosch or Ducati ignitions. It is not compatible as a replacement for SEM ignitions and it is not compatible as a replacement of Bosch ignitions with contact breaker. Our ignition differs visually from your original ignition. However, it works flawlessly.

If you need a replacement for a Bosch ignition with contact breaker you can order the article with ebay number: 321366822778



I can't find the timing specs on the 153 but the same saw with a 85cc engine, the 133 is 2.1 to 2.5mm btdc. What I can do on mine is mark TDC via the dial indicator method and also 2.3mm btdc. Running it I also can see where the timing is set from the factory and if there's an advance (or retard) curve built into it.

Your thoughts?

thx again.


ps:
There are new SEM replacement units available. I didn't make note of them as I have the Bosch.
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Old 03-15-2016, 09:17:22 AM
bigGURN bigGURN is offline
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Default Re: Sachs Dolmar ignition woes

Of note, the 133 and the 153/163 are completely different engines. I have both and can attest that they are different monsters. But the timing for most of the saws I have come across with the Bosch unit is usually in the 2.1-2.5mm btdc range.

Under the shrink wrap of that ebay unit is a a module and a wire connector, the module looks just like a Nova. After I did my mod, one of the European collectors bought a saw and it had one installed, when they cut off the shrink wrap, they revealed it looked the same as what I had done, just mounted to a different plate, for six to eight times the cost.

On my S6000 and the Stihl, both ended up with the ignition in the stock timing. For whatever reason, the Dolmar 133 wanted to be very advanced to run right. I have had a few husqvarna's that had to be slightly advanced, but never anything like that first Dolmar. The dolmar 133 is still being used as a firewood saw, getting quite a few hours every year, with no issue, my suspicion is the key on the Dolmar was probably partially sheered (I didn't ever check to see) and that because it was sheered, that was what required the extreme advance on it.

The Nova unit is energized just like a condenser in a points ignition, from the magnetic pulse off the coil, the current travels to the transistor inside the module that once it reaches peak, discharges the higher accumulated current back to the coil and out to the spark plug. The factory unit worked under the same principle, the charge came from the coil, but it required a magnetic field for the trigger to initiate the release of the energy, this modification simply removes the trigger requirement.

To use the SEM unit, you also have to have the flywheel, if you go the used route, the cost usually averages $125. For a new SEM unit and a used Flywheel, closer to $200, new SEM and new Flywheel, is around $300 from the dealer. I've done those conversions before on Husqvarna 2100s, it works great, but often the cost is more than the saw is worth.

Last edited by bigGURN; 03-15-2016 at 09:35:10 AM.
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Old 03-15-2016, 10:50:12 AM
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Default Re: Sachs Dolmar ignition woes

Super thanks. I'll go online and find a nova unit. I'll time it at 2. something and see how it goes and post up.

edit: Ordered two for $25.
Looking at your pics, it seems the + is grounded with the - going to the coil. Correct? Or does the + go to the stop switch.

Last edited by I like oldstuff; 03-15-2016 at 11:11:49 AM.
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Old 03-22-2016, 08:58:56 PM
bigGURN bigGURN is offline
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Default Re: Sachs Dolmar ignition woes

The - goes to ground and the + to the coil with a pigtail y that goes up to the kill switch so that the switch grounds the coil and the + side in the off position. .
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Old 03-22-2016, 11:09:46 PM
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Default Re: Sachs Dolmar ignition woes

The Nova units came yesterday.
But,, I'm going to do this repair first which should retain the advance curve.

http://www.arboristsite.com/communit...nition.256095/
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Old 03-22-2016, 11:13:28 PM
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Default Re: Sachs Dolmar ignition woes

Good luck, let me know how it goes
Some seem to have luck with his method and others not so much, so I'd like to see how it works for you.
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Old 03-23-2016, 07:45:05 AM
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Default Re: Sachs Dolmar ignition woes

I'll give it a shot next week when the various capacitors come in. I'll remote mount it temporarily outside the saw to look at heat generation etc. If it's a bust (who knows what is actually faulty in the ignition system) I'll do your Nova mod.

I'm glad to have two methods to resurrect this thing as there's a three foot maple at a friends house that has to come down.
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