Early Stihl 090 Flywheel / Coil Clearance Issue

[skippymud]

Hello All

FW = Flywheel
There are no visible markings on the saw. No S/N etc

I have a (what appears to be an early-ish) 090 that I acquired during mid-repair of its ignition system. The previous owner tried to convert it to Electronic Ignition. That didn't work. I am in the process of converting it back to Points & Condenser style. Bought the new ignition system complete from Lil Red Barn

Issue is that the Flywheel Magnets make contact with the Coil Legs. This issue was also present when the Electronic Ignition was installed prior. In order to find out exactly where the FW was making contact with the Coil, I removed the coil and "painted" the ends with a Sharpie Marker, then re-mounted it with the FW and gave it a few spins. Where the Sharpie got rubbed away is where the FW magnets make contact with the Coil Legs

A Further Mention:
I also bought an aftermarket FW from Lil Red Barn some time ago in hopes that it would fit just right, and it did with no contact between FW and Coil Legs, but the top-side of the FW does not allow correct mounting of the Starter Cup so I couldn't use that FW. Eventually I removed the 4 magnets from the new FW and installed them on the original FW. Same issue - FW and Coil Legs touch and rub abruptly

The OD of the original and new FW are exactly the same. The wall thickness of both are exactly the same

I am at wit's end on this issue

 

[Bob Hedgecutter]

Not a platform I have a lot of time with, but if I go look- I will have the service manuals for.
First thought would be worn crank bearings allowing the crank to ever so slightly run out of true.
Second would be the fit of aftermarket parts and tolerances compared to OEM.
Third would be a size variation between electronic ignition parts and points ignition parts.

 

[skippymud]

Howdy there Bob

I have the service manual but that was no help to my specific issue. Both Crank needle bearings are tight. I am having exactly the same issue with both the OEM (Bosch) and Aftermarket FWs. Size variation - yes for sure. I will have to put this one aside for while and think on it

Ken

 

[Bob Hedgecutter]

Obvious " out" would be to slot the pick up bolt holes slightly if there is clearance enough for it to slip back towards the crank.
Would involve some math to calculate the clearance.
I know there was a crankshaft change during the production run, from a bolt on end cap tp the con rod lower to a sealed unit- possibly was a similar parts step in flywheels somewhere along the lines.
Visibly no different on the exterior, but differing internally- I would have to go through a lot of old paperwork to check, could possibly be 070 parts thrown into the mix?
You perhaps need to find someone that owns several and knows about any and all variations- around here you get a lot of plastic consumer saws- not many big old 130cc plus type monsters.