FS55RC, extensive t/shooting & repairs done. Dang it...still won't start. Long read, apologies.

[StarTech]

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.

 

[Martepm]

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

 

[StarTech]

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 (may have been superseded)

Plus the 4140 120 0612 or 4140 120 0619 (superseded to 4140 120 0619 (Zama C1Q-S186B) as of 10/15)) does not work with the 4140 400 1303 coil or its supersede.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.

 

[Martepm]

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.

 

[bertsmobile1]

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 .

 

[Fish]

Insufficiently torquing the flywheel, it will just shear again.

 

[Hammermechanicman]

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

 

[bertsmobile1]

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.

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 .

 

[Fish]

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.

 

[Fish]

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.