Sachs Dolmar 120 runs 4 minutes, quits, won't restart

[kspakland]

I was given a Sachs Dolmar 120 chainsaw recently, and it runs really strong, for about 4 minutes. Then it quits, and will not restart. It's getting fuel, and everything is clean and it has a good spark plug. I am suspecting the ignition is crapping out when it gets warmed up. Does anybody have any ideas what I should look for, and how do I do a test on the ignition (resistance readings, etc) ? Ripping a 20" piece of juniper lengthwise and the engine doesn't even bog down and the chips really fly. When it's cold, I blip the choke 3 times and the saw fires up on the first pull. I think it's worth fixing, but I am not familiar with the Sachs, this is my first one.

 

[JasonBmac]

Grab an old but "good" plug. Break off the ground electrode so that the centre electrode is surrounded by the threaded portion. THis makes testing spark much more certain. Stick it in your pocket. Go saw.

When the saw quits, IMMEDIATELY get this test plug on the lead, and test for spark. If it's a heat related failure, you probably don't have long to test before it'll spark again... So know how to get in and know where to ground the plug body before you get goin'. Test for spark in a shady place.... Sunlight makes a difficult test.

If spark's OK... It gets tricker.

Can you describe how the saw goes about quitting? Does it begin missing? Is it like someone hits a switch? Does it lean bog or rich blubber/smoke? Therein lie clues.

J

 

[Kenskip1]

If it is getting fuel and has spark then I would suspect low compression. Lets put this into perspective. When the engine is cool things contract. When things get hot they expand. This sounds what is happening to your saw.As the saw heats up the clearances expand thus loosing compression. If you have a compression tester handy this could tell the story. Sounds to me like a worn set of rings. Buy the way, welcome to the site.Ken

 

[kspakland]

I also noticed, when I set the saw on its right side for a while, there is a gas leak coming from someplace near the carburetor, so I am going to have to check that out also. When the saw quit, it was idling, I was between cuts and setting up another log, and it just quit. The saw wasn't bogging due to over/under carburetion, and was running flawlessly. I will do a spark and compression test when it's running again. I suspect the compression is good, as the saw has plenty of power and it's almost impossible to bog it down when cuttting and it's making some serious chips. Thanks for the warm welcome to the site, I am looking forward to being an active part of the community. Kev

 

[barton174]

I just had an interesting similar problem with my JRed 490... I installed a new fuel tank vent line, and it ended up that it was kinked down inside the saw (it goes down inside, then drains out the bottom of the saw, where the halves split.)... It would run great for a cut or 2, then would start to bog down, and then would flood and die... Let it cool down, and it would run great for a little bit again, then flood and die... Open up the cap when it was hot, then get it started after a plug drying, then it would start to get lean...

Fuel in the tank was getting heated up and pressurizing, which pushed extra fuel into the carb... When opened hot and restarted, fuel was getting used and fuel tank had a vacuum on it, and would lean out...

Mike

 

[kspakland]

Even after letting the saw sit and cool quite a while, several hours, it still won't start. It's getting plenty of gas and has a boatload of compression. I checked for spark and have none. What is the testing procedure to check out the ignition system to find the faulty component ?

 

[discounthunter]

Even after letting the saw sit and cool quite a while, several hours, it still won't start. It's getting plenty of gas and has a boatload of compression. I checked for spark and have none. What is the testing procedure to check out the ignition system to find the faulty component ?

start small. get a new plug,or get two just to be sure. this saw is used,was it cleaned. clean out around the coil check for run on the coil and flywheel.hope this helps. sd 120 is a great saw.

btw the leak when on its side it the tank vent. hose is probably dry rotten and or fallen of.try fixing this too before replacing ignition parts.

 

[kspakland]

Well, I managed to kill off the saw the rest of the way .... I had a 3 point puller attached to the three screw holes in the flywheel, and instead of the flywheel coming off, the tip of the crankshaft broke, and bent part way over, can't even thread the nut on it now. So, it appears I now have a parts saw for sale unless somebody has a crankshaft and an easy idea how to remove the flywheel .......

 

[Gumnuts]

Bummer......
.....will check on whether i got a spare crank / will know by next friday.OR are you able to post pic of the crank stub thats left ?......ways and means around that......!!!

 

[kspakland]

Took 4 tries, but I got a pic ........

 

[roncoinc]

Took 4 tries, but I got a pic ........

Major bummer man..
i love my 120..
next time leave the nut on flush with the top,then pull and tap with a hammer..
as nice a saw as it is,aint worth THAT much work..
god luck..

 

[kspakland]

Meanwhile, how do I remove the goofy flywheel? Use my torch and heat it up around the center where the crank sticks through it ? I'm open for any and all ideas, I think this saw is worth saving. It showed me its potential today for the 4 minutes it ran, I couldn't get it to bog or slow down buried in 20 inches of wood and making serious chips ...

 

[crane]

Sorry about the saw.

+1 with putting the nut on flush for the next time.
Careful with the heat......too much and you'll watch it puddle on your bench.
I wouldn't entertain the idea of trying to salvage that crank. That looks like a "few" threads are missing.

 

[Jacob J.]

I have an extra crank that's good that you can have. It's in a case that's junk but the crank itself is good.

 

[motomedik]

I have a 120 that has no spark unless I bypass the plug, grounding the cap and pulling it off the head to get a spark- then it seams to run fine, and they do run nice. Mine's kinda the opposite of your problem. It does seem that the ignition is the weak link in these saws.
If it's like mine, when you get under the flywheel, there are two parts; a coil and a module. I have a spare set and swapped 'em onto my saw, mixed it up a bit and got it sparking as mentioned above. Wish mine ran reliably, love it when it runs:chainsawguy:

 

[Oldtimer]

When it dies, take off the gas cap, and try to start it again.
Like the poster above said, it's prolly a venting issue.
When I first bought my splitter, it would start instantly and run great for about 30 seconds...then die. It was the gas cap. I drilled a 3/32 hole in the cap, and it's run fine since..I think the previous owner sold it because it kept dying..

 

[weimedog]

Bump...any ideas for Moto's Dolmar? Do ignitions from other brand saws swap over?

 

[kspakland]

I would have to doubt that ignitions from other saws would work, as it seems each manufacturer wants to sell their own parts (and as many of them as they can, it seems). But, it would sure be nice if there was more interchangeability in the world of power equipment. He may get lucky with his and find a system from a different model Dolmar, or perhaps a Stihl, both being German made, that would work.
On a happy note, I believe I have my 120 problems figured out. Ordered a set of rings for it, as the P&C look real good and P&C kits are not available. I shut the saw down after running and immediately pulled the spark plug, it was soaked in gas, dripping wet, so that points to carburetor. I ordered a kit for it today and should be rebuilding the carb over the weekend. I plan to tear the saw down and not just run it as it is, and do a complete cleaning and de-carbon the port. My thinking is a clean saw is a happy saw and a happy saw runs better. Or did my brain take a trip and not come back?