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Howdy all.
Been looking for insight on above issue for a long time & on numerous sites....to no avail. There is a hidden problem somewhere here I'm missing.
Seen some scholars respond here so thought to make one more attempt to request some input to figure out what I am missing.
This is a doozie for sure & there isn't much left!

To give some background, I have just closed my industrial petroleum maintenance & compliance testing company. Retiring after 26 years. (Thank God!)
So yes, I'm a t/shooter & very mechanically incline, in the electronic's field also.
Since I have time now, thought to repair some weed eaters & blowers friends have given me over the years. Some I repaired & gave back. Others were dumped off & they bought new ones.
I like to tinker in the garage in my spare time to keep my mind sharp. Thus, I'm their dumping place.

To the point & 1st project...my own 06' FS55RC with easy2start. By calculations about 200-300 hr's of use at/for home in the 16 yr's I've had it. Gradually over the years it got harder to start & keep running.
Compression is at 130 lbs. The following have been replaced so far; fuel & air filters, fuel line, carb, spark plug, coil & flywheel.

*Spark seemed weak so replaced coil,... no joy.
*New complete fuel system. Bulb filled up quickly & looked like it was ready to fire up,... no joy.
*Had spark but wondered about timing. Sure enough flywheel key got sheared off. Installed new flywheel with green loctite to prevent future movement & let it dry for a week. Used business card to set coil air gap, making sure both induction points didn't move,... no joy.
*Removed muffler & removed spark arrestor screen even though it was clean,...no joy. Cylinder walls & piston looked as good as one would expect with little use. No scoring, hardly any wear.
*Today installed new starter rope & spring (wore it out in this process) & tried that, no joy.

Took starter off & got smarter..used 1/2 elect drill to turn motor over (clockwise spin) to check spark, still looked good. Several times tried spraying starter fluid in carb, then in cylinder & spin motor with drill...nothing. Spark plug seemed dry to me. Tried same with 50:1 Stihl oil&gas, nothing again and even noticed vapor being expelled out exhaust without a hint of attempting to fire up. Plug again seemed dry to me. Put a sample of both fuels on bench & tried a lighter. Both lit with ease & burned for about 20 sec's. Previously sprayed head with starter fluid & placed spark plug on it, it lit & burned off.
Just to check compression again as one might ask....130 lbs. Added oil, rotated motor in tilted circular motion to cover walls/rings then spun with elect motor to coat the rings & walls. Attached gauge after that and now have 170 Lbs.

So there you go. By all right's it should have at least fired. Still...nothing, not even a hint of ignition. I'm completely dumbfounded now.
From my many years of t/shooting...in general,...one thing is clear....all the improvements I've made have had no effect whatsoever.
Thus, there is another unknown issue that hasn't been addressed.
Just now learning about crankcase pressure. Perhaps?...but it should have fired after spraying in carb or cylinder.....correct?

Noticed, spark plug seemed dry throughout these test's. Yet it had the ability to ignite starter fluid once outside the cylinder. (WTH?)
Checking TDC, highest piston point...was between both magnets on the flywheel, on the coil side of steel induction frame.

Wanted to sell this & others for added income. At this point I'm about even for what I can sell it for, maybe $125.
Hate to throw it in garbage after spending that amount to get it running again, if you know what I mean.
Hoping one of you scholars can step in to help recover my expense so at least I'll break even & learn from my mistakes.

Sorry for long post but being as specific and factual as possible,....as this is not your normal everyday issue in the many, many "won't start" post's I've read.
My thanks in advance.
Mart

The one thing you have not checking are the crankshaft seals. At that age they are probably dried out and not sealing the crankcase. This would result in the air/fuel mixture being pushed out of the crankcase around the seals and not into the cylinder. This is the only thing I can see which you have not considered.

Thanks Rivets, just learning about that now.
Is there some test to determine their integrity? Haven't gotten that far yet.

Just like any oil seal, you can tell how dry they are by poking them with a screwdriver. Rubber should be flexible. At that age and the amount of $$$ you’ve stuck into the unit I’d probably just replace both of them

Also check flywheel key for shearing.

Flywheel key shearing was addressed & found at fault. Flywheel replaced.

did you replace the spark plug? Compression changes the voltage needed to fire so a carbon track that might jump under compression might be fine outside the cylinder. Personally at this point I would pull the plug, squirt a half teaspoon of fuel into the cylinder thru the plug hole and try again.

Yup, been there, done that as mentioned in original post.
With all due respect in helping....way past that point in t/shooting. A far reaching & more deeper issue is at hand.
So you might understand, read about 8-14 hr's of post's on this subject from multiple sites.
I'm far beyond the "normal" everyday t/shooting.
Something else is at hand that hasn't been covered.
But thx for input.

Actually it has probably sheared again as it is a taper and putting anything, including loctite on a taper prevents it locking tight
The other biggie is the transfer ports
As rivets has already mentioned the crankcase is pressuriised by the descending piston and when the hole in the side of the piston aligns with the hole in the cylinder wall the charge in the crankcase is forced into the combustion chamber .
These often get damaged
Now historically we do not want to know what you have done
When we need is for you to do what we ask now and give us the results of the NEW test
SO a couple of things , in no particular order
1) as already requested do a new fuel down the plug hole test
2) remove the flywheel , check the timing key and clean both side surgically clean
Bring the piston to TDC and mark the side of the flywheel where it enters the coil legs with a white paint pen .
4) strobe the flywheel with the plug laying on the side of the block and look at where the index line you just made is
It should be about 30 deg away from the coil leg when the strobe flashes .
This is a rough test to verify that the flywheel is the correct one for your engine
5) Pull the carb off the engine but leave the fuel lines attached
Turn it sideways & blow air through it to simulate normal running
High volume low pressure is best
If the carb is working properly you should get a strong flow of atomised fuel coming out of the engine end
Do this with a tank chockers full then 2/3 empty .
6) if you have a propane torch, adjust to a fine flame and play it across the plug hole.
You should see the air:fuel ignite as it comes out of the cylinder when you crank it with your drill .
An old diesel engine glow plug works well for this
7) And of course the old hot plug is also worth a try
Heat one up with an oxy torch using a very lean flame to burn off the residue that you can not see that may have deposited on the plug when the engine did not fire.
As you probably already know modern fuels ( which are not petrol ) can be very conductive at combustion pressures .
Install the plug wile too hot to hold in bare hands & see if that will fire .

And so we know exactly where we stand
I ask people to do tests that all of the techs here will understand the reasoning behind
If you do them & respond then I ( or others ) will take things further based on these results alone ( what was done in the past is meaningless ) .
If you can't be bothered to either do them or respond with the results then I can't be bothered devoting any more time to your problem .

The order is not important , however it best suits you is fine
Doing all of them is important

Lots of new parts sourced from evilpay / ammozone are actually rejected defective parts bought as scrap metal then sold to cheapskates on line .

Nicely done Bert. Appriciated. Exactly what I was hoping to find here.
I printed your instructions for the work bench & will go thru them one by one.
I too had suspicions about the replacement flywheel but found myself trying to convince my myself that couldn't be the problem.

This has become a personal challenge & a driving force to figure out what is happening.
I will be back to report findings once all are completed.
My thanks for all the input.

Are you sure you used the correct ignition coil and carburetor?

I ran across the following in a service bulletin for the FS55.

Using the wrong ignition coil would be enough to throw the ignition timing off.

This is the coil I got;
ENGINERUN Ignition Module Coil Compatible with Stihl FS46 FC55 FS45, HL45 HS45 String Trimmer Parts OEM 4140 400 1308
and flywheel;
NEW OEM STIHL FLYWHEEL FC55 FS38 FS45 FS46 FS55 FS55R HL45 KM55 KM55R MM55 MM55C
and carb;
HUZTL FS45 FS55 FS55R Carburetor for STHIL FS38 FS46 HL45 FS45C FS46C FS55C FS55RC KM55 String Trimmer Weed Eater C1Q-S97

I would have to get with my dealer to see if the 4140 400 1308 is the replacement for either the following coils.



Also the service bulletin listed a 4140 400 1303 to use with the new version of the crankshaft. (may have been superseded)

Plus the 4140 120 0612 or 4140 120 0619 (superseded to 4140 120 0619 (Zama C1Q-S186B) as of 10/15)) does not work with the 4140 400 1303 coil or its supersede. You must use 4140 120 0603 (Zama C1Q-S66). Again I would need to get with my Stihl dealer to see if any supersedes are done lately.

Just for grins went to check TDC more carefully & compare old flywheel to new. Old one clearly has thinner magnets. At TDC the coil is on 2nd magnet as it rotates clockwise.

There is nothing that you will come across that some one else has not also had to deal with .
The bad parts problem is getting chronic & I wince every time a customer brings in an impossible repair with a pile of cheap parts fitted.
Every time the "new" parts were faulty or just plain wrong for that machine .
When it comes to flywheels on hand held engines there are literally hundreds that will fit as the taper seem to be almost universal and there is only about 1/2 dozen different crankshaft diameters
By far are the worst are the "tune up kits" that come with a carb, purge valve, plug, coil both filters , fuel lines & gaskets .
Always at least 1 wrong or defective part in the kit .

Insufficiently torquing the flywheel, it will just shear again.

I have never had any luck with any of the Ebay/amazon kits for stihl pdoducts. Every part is usually crap.

Martepm said:

Just for grins went to check TDC more carefully & compare old flywheel to new. Old one clearly has thinner magnets. At TDC the coil is on 2nd magnet as it rotates clockwise.

Click to expand...

The flywheel spins counter clockwise ( double check with your starter )
All engines fire before TDC
A magneto developes peak power as the leading magnet is just starting to pass the furthest leg of the coil.
Coils get positioned in different places according to the space available so in many cases the models will have identical looking flywheels but the key is in a different spot which is why I mark the flywheel and check it against TDC.

A lot of home mechanics get caught out because they do not understand the principles of magneto power generation.
The faster a coil passes a magnet the higher the voltage it produces
These engines are designed to be at peal coil power at full speed which is 7,000 to 12,000 rpmSo if you are getting a big fat spark at those speeds then you get a pathetic tiny spark at the 500 rpm pull start speed and the one at 1500 to 3000 rpm ( idle speed ) is not much better which is one reason why they burble at low speeds, because the engine is missing .

Home mechanics who are used to seeing big fat sparks that battery discharge ignitions ( called Kettering type ) give at idle see ( or don't see ) the tiny fril sparks these engines give off at cranking / idle speeds and assume they have a spark problem, when none exists .
So they then start swapping ignition parts and end up with a mess because as Star has just shown, the manufacturers regularly change parts during a production run and not all parts will work with the others .

There have been a few different flywheels made for that series, but I always replace one with the same one/same part number to be safe.
The great thing with that model is that the same powerhead is on the fs38, so I just slapped an fs38 powerhead on the fa55 straight shaft, and it runs great. I even swapped the fs38 engine on my old fs90 shaft, and that runs great too.
It even handles the tri-blade and the chainsaw attachment just fine.

But the flywheels that I sell on e-bay are two of the three, and they all seem to work the same, and the coils are all the same.
For the hell of it, I made a youtube of removing the clutch/flywheel on these, It is a fs56 in the video, but it has the same clutch, drum as the fs38/45/55.

Fish said:

Insufficiently torquing the flywheel, it will just shear again.

Click to expand...

The clutch carrier is torqued to 12.5 ft/lbs.

Thanks guy's.
The flywheel does indeed turn clockwise. That was checked after spinning motor with drill & noticing fuel mist from exhaust after pouring fuel in cylinder & replacing spark plug. "How can that much fuel expel & not fire-up? Am I spinning in the correct direction?" That's when I checked starter direction. With that in mind, went back to verify magnet position at TDC. What I see is 1st magnet passing "under coil" (clockwise) on compression & 2nd magnet passing under coil at TDC. (TDC is pictured above, pic# 0757) Without being a mathematician in physic's, that tells me the key is in the correct position and magnet timing is correct.
The new flywheel is Stihl's replacement # for previous one. Old one had separate steel sleeve on shaft for clutch to compress flywheel onto shaft. New one has sleeve molded into flywheel. And yes Fish, torqued clutch with as much umph as it took to remove it, maybe more.

Fish, nice trick in video to remove flywheel. However, I used a gear puller. . (tension it up & smack the puller's stud...pop's right off)

After hearing of all the aftermarket parts problems....feeling kinda depressed & looks like I may have wasted a lot of time & $'s. Thinking maybe I should just chuck the thing in the garbage & cut my loss's. However, though my ambitions are diminished, I will continue & perform the test's Bert provided & see where that takes me.
Will advise.

StarTech said:

The clutch carrier is torqued to 12.5 ft/lbs.

Click to expand...

Yeah, I know there's more than 12 lb on it.
Thx

I will make a suggestion for a test. You need primary compression, (crankcase) secondary compression (cylinder) spark at proper time and a vaporized air fuel mixture.

Remove carb and sparkplug. Turn unit over with plug hole pointing down and pull starter rope about a dozen times to clear any fuel from crankcase and cylinder. Install new sparkplug. Spray a VERY SMALL AMOUNT of starting fluid, not gas and not carb cleaner, into the intake and try to start unit. If it fires you have at least enough primary and secondary compression to run the engine and spark at the proper time. If it doesn't fire you either have bad crank seals, scored or worn cylinder and rings or spark at wrong time.

Thx.
That was all done/coverd in 1st post. Not a hint of any attempt to start.

Where are the magnets at TDC?

This is TDC as precisely as I can make it..
Thx.

Martepm said:

Thanks guy's.
The flywheel does indeed turn clockwise. That was checked after spinning motor with drill & noticing fuel mist from exhaust after pouring fuel in cylinder & replacing spark plug. "How can that much fuel expel & not fire-up? Am I spinning in the correct direction?" That's when I checked starter direction. With that in mind, went back to verify magnet position at TDC. What I see is 1st magnet passing "under coil" (clockwise) on compression & 2nd magnet passing under coil at TDC. (TDC is pictured above, pic# 0757) Without being a mathematician in physic's, that tells me the key is in the correct position and magnet timing is correct.
The new flywheel is Stihl's replacement # for previous one. Old one had separate steel sleeve on shaft for clutch to compress flywheel onto shaft. New one has sleeve molded into flywheel. And yes Fish, torqued clutch with as much umph as it took to remove it, maybe more.

Fish, nice trick in video to remove flywheel. However, I used a gear puller. . (tension it up & smack the puller's stud...pop's right off)

After hearing of all the aftermarket parts problems....feeling kinda depressed & looks like I may have wasted a lot of time & $'s. Thinking maybe I should just chuck the thing in the garbage & cut my loss's. However, though my ambitions are diminished, I will continue & perform the test's Bert provided & see where that takes me.
Will advise.

Click to expand...

This is relative to which you are looking the flywheel. From the drive clutch side it turns CCW; from the recoil starter side it is CW.

Also being 2 cycle you can't if spinning the right just looking at the exhaust mist. When 2 cycle is properly in some equipment the engine can run either way; especially in golf carts.

Gentleman, to eliminate further questions about rotation, I submit this pic. Starter rope pulls from left side & motor turns clockwise.
I feel some of you haven't read my 1st post thoroughly.
Would it be possible to eliminate this rotation issue & move on?
Thx again for all the input.

Fish, thanks for pic's. Without specialized micrometers & such tools, measuring down to .01" on outside flywheel dia movement seems to be not that important. Am I wrong on this point? Is it that critical? Again, I submit TDC as close as I can get it without high tech measuring tool.
It may be 1/8 or 1/16th off flywheel O.D. for TDC.
Am I correct in this thinking? Can't believe that small of a measurement would not make a motor run.
JMHO.

It doesn't take being off by much.

Are those aftermarket parts?
I have never seen an e-z start fs38/45/55 around here.

Thanks for the photos Fish
And I think that nails it
Martepm's magnets are at lease 5 deg out of time if his engine was actually at TDC when he took the photo.
Timing on these engines is critical because of the very short stroke

Mart,
To get TDC very accurately you do not need any measuring tools
You need a bolt with the same thread as the spark plug , a sharpie type fine point marking pen and a dressmakers measuring tape , although the latter can be replaced with a piece of string .
Method
1) bring the piston up near TDC then screw the bolt in till it touches the piston
Mark the flywheel with the sharpie against some index point on the engine that is thin and can not move .
Rotate the engine backwards till the piston hits the bolt again and make another mark
TDC will be 1/2 way between these 2 marks which is what the measuring tape is for .
Alternate method
Screw the bolt in till it touches the piston and make your mark as before
Rotate backwards and make your mark
Rotate foreward a little and move the bolt 1 flat further in then repeat
Keep on doing this thill the piston stops at the same point backwards & forwards
If using this method it works best to stick a piece of masking tape on the flywheel so the lines are clearer
And some different colours helps as when you get near TDC there will be a lot of lines very close together .

FWIW
THE spark is timed by a chip inside the coil that measures the voltage being generated in the coil and when it gets to a specific vale the circuit triggers the spark .
This method of timing the spark. called a Hall Effect Trigger automatically advances the spark as the engine speed increases because the rising rate of a coil is proportional to the speed that the magnets are moving past the legs .
As mentioned previously the spark at cranking speeds is marginal at best so if it comes slightly out of time then no bang .
Way back in post # 9 I asked for tests & laid out how I treat threads here so for me it is bye-bye till what I asked for has been done & the results posted .

"Martepm's magnets are at lease 5 deg out of time if his engine was actually at TDC when he took the photo."

Yes Bert, had a "marked nail" in cylinder while moving piston up/down & took the pic when movement was centered between both movements. Precisely done I will add with eyesight, no guessing involved.
Thx. Will follow up tomorrow on your procedure & advise.....

bertsmobile1 said:

FWIW
THE spark is timed by a chip inside the coil that measures the voltage being generated in the coil and when it gets to a specific vale the circuit triggers the spark .
This method of timing the spark. called a Hall Effect Trigger automatically advances the spark as the engine speed increases because the rising rate of a coil is proportional to the speed that the magnets are moving past the legs .
As mentioned previously the spark at cranking speeds is marginal at best so if it comes slightly out of time then no bang .
Way back in post # 9 I asked for tests & laid out how I treat threads here so for me it is bye-bye till what I asked for has been done & the results posted .

Click to expand...

Yes Bert, I understand your position. I think like you do. (Don't waste my time with brain-dead idiots!)
I still have your printed-out post with instructions here on my desk.

Not to discount your info & helpfulness, but have had & still have duties around here as a rural home owner.
In this case & lately, gathering refuge, recycling & yard waste into the truck to take to the dump. Usually once a month.

FYI, I am not a repair shop for these things, just a simple home owner on retirement trying to fix & sell some equipment.
I hope you'll allow me some time to dive back into this issue.

I have responded to others when questions arose to be continuative on the problem. I still have to get things done as you requested/instructed.

This project has captivated my mind. I want to resolve and learn from it & perhaps make a few $'s from it if I can.
Thx for your patience.

Manual.

Thx fish, looking at flywheel area chapter now.
Time to thaw dinner. Will pick-up in morning.

It doesn't discuss the flywheel much, but the manual will become useful.

Thx.