Author Topic: Chainsaw ignition timing  (Read 418 times)

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Offline Giles

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Chainsaw ignition timing
« on: October 11, 2016, 09:52:15 pm »
Didn't really know where to post this bet here goes-----
A friend that also works on chainsaws, asked me an interesting question. He asked me what was the position of the flywheel, in relation to the ignition module at the moment of ignition?
Like---the flywheel has two magnets and the module has two pickups. At what point of rotation does the module produce a spark?

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Offline RoyM

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Re: Chainsaw ignition timing
« Reply #1 on: October 11, 2016, 10:31:20 pm »
Just as the magnet moves away from the coil. The magnetic field around the coil collapses inducing a high voltage in the secondary winding.
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Offline Giles

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Re: Chainsaw ignition timing
« Reply #2 on: October 14, 2016, 09:57:59 am »
My friend, that asked this question, brought the Echo CS330t in question. Compression is 145# and carb is clean.
When pulling over, it will not even attempt to start, even with starting fluid. Blue spark from sparkplug with moderate pull over.
Seals and boot are good.
Out of curiosity, we hooked up an automotive timing light to determine spark. Rotated flywheel forward with cordless drill.
Spark occurred  nearly 1/4 revolution after flywheel magnets passed coil! Changed coils and both  coils presented same results.
From the markings we made on flywheel, spark is occurring after top dead center with piston rotating down app. 1/4" ?
Ignition way late.
I think both coils are bad? ?

Offline RoyM

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Re: Chainsaw ignition timing
« Reply #3 on: October 14, 2016, 10:20:50 pm »
Flywheel key is sheared
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Offline Giles

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Re: Chainsaw ignition timing
« Reply #4 on: October 14, 2016, 10:40:26 pm »
Spark occurred  nearly 1/4 revolution after flywheel magnets passed coil!

Has nothing to do with Flywheel Key.

Offline Al Smith

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Re: Chainsaw ignition timing
« Reply #5 on: October 16, 2016, 04:10:15 pm »
Not to sound like a smart alec but did you turn it the right direction .The spark should be 26-30 degrees before top dead center .Usually if you try to turn the flywheel with a drill motor it's turning the wrong direction for the right hand threaded nut and you unscrew the flywheel .I sent the flywheel of an old gear drive in orbit around my garage doing that and just missed my wifes Cadillac .I'd have never heard the end of that .
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Offline Giles

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Re: Chainsaw ignition timing
« Reply #6 on: October 16, 2016, 05:10:03 pm »
Al--When sparkplug is removed and the flywheel nut is torqued, I have never had one unscrew. I use a variable speed cordless drill motor and I start slow and then increase speed. When finished, I remove socket from nut while turning to prevent shock.
Also a good idea to make sure piston rings are lubricated if spun very long.

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Re: Chainsaw ignition timing
« Reply #7 on: October 16, 2016, 09:55:20 pm »
The spark should always occur after top dead center.    How much ATDC is determined by the manufacturer.   
They do not like to much advance because it can be hard to turn over.   

I have never seen a timing problem on a saw like you are talking about especially with two different coils.   If it were me I would start over and double check everything else you have done.

One of my test I like to do is to squirt some mix into the carb and then pull it over with no choke and wide open throttle.   after about 5 pulls if it does not fire at all then pull the plug and see if it is wet or if it is dry.  I do not use starter fluids on 2 cycle engines because there is no oil and the rings do need a small amount of oil to help seal for compression.

If the plug is wet then double check the spark.   Also double check the compression.   Blow the plug dry with compressed air and blow out the cylinder through the spark plug hole.   Pull the rope a couple of times and then blow it out some more.   Put the plug back in and pull it over again with wide open throttle no choke and see if it fires.   If it does not then check the plug again.

If the plug is dry then double check the crank case pressure because the fuel is not moving from the crankcase into the combustion chamber.   I would also double check the compression in this case also.
If you have fuel, compression, and spark it should fire.   
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Offline Giles

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Re: Chainsaw ignition timing
« Reply #8 on: October 16, 2016, 10:31:48 pm »
"I have never seen a timing problem on a saw like you are talking about especially with two different coils."

Neither have I --and I have worked on small engines for over 50 years.
I agree with all you say about checking, but this is wasted time when the spark apparently occurs with piston down 1/4 to 3/8"

If you have fuel, compression and spark it should fire.

But if ignition is not at the right time???

Any time I check for a solution to a problem, I always double check and sometimes triple check. Sometimes simple things cause big problems.
Have you ever heard of a person using an automotive timing light on a chainsaw?  Might be that I am putting too much confidence in timing light.
Thanks for your input.

Offline 660magnum

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Re: Chainsaw ignition timing
« Reply #9 on: October 16, 2016, 10:43:11 pm »
Automotive timing lights have given odd readings on chainsaws before.
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