by Skywatcher » Tue Apr 13, 2021 9:36 am
Hi Again
Figured I'd give an update on this machine. The mechanic working on this machine (Larry) pulled the flywheel and found that although the key wasn't sheared, it was just slightly stressed. Therefore, he installed a new key, set the flywheel onto the crankshaft with Loctite bearing mount and torqued the bolt to 110 ft-lb. This got the engine running perfectly.
Ran the engine and drove the unit around for 30+ minutes without a glitch, so was sure he finally had the thing beat. Shut the engine off and had a coffee, went back out to the unit to drive it back to the customer's house and it wouldn't start--no spark, another dead coil. By this time he was getting thoroughly frustrated with the unit.
He got in touch with another old mechanic who suggested a few things and possibilities. The diode that I had installed in the ground wire may not have been dumping the voltage from the trigger coil and transistor quickly enough. He also sited an analogy which 38 alluded to. When you're driving down the highway and the vehicle in front of you is pulling a trailer, when a signal light is turned on, all the lights on the trailer flash together, this indicates a bad ground. This is possibly happening with the Stiga as it ran flawlessly for 20+ years, then suddenly started eating coils.
Larry came by my shop yesterday and told me what he ended up doing. He took the entire wiring harness to pieces, including the multi-point ground beneath the right side control console and removed the diode from the stop wire. Stripped the paint off from under the mounting points of the common ground and discarded the flimsy sheet metal screws. Drilled the mounting holes out to ¼", applied silicone grease to the metal and bolted the grounding connector block to the frame with ¼" bolts and nuts. Every terminal and connector of the harness was cleaned and reassembled or reconnected with silicone grease on any metal to metal contact to help prevent oxidation.
When everything was put back together with a used coil taken from an old Sears lawn tractor (we cross referenced the part number to make sure), the machine works perfectly and restarts every time. This ended up being the type of problem that you can't say "Here's where the problem was", but you can only guess that in everything you did, you solved the problem somewhere along the way. Larry figures he's spent 8 hours of his shop time plus several hundred dollars in coils and other parts repairing a machine that broke down when he was voluntarily servicing it for the widow who lives across the street. How does one justify that much lost time and expense? All the best,
Sky
A person who sees Quality and feels it as he works is a person who cares.
A person who cares about what he sees and does is a person who's bound to have some characteristics of Quality.
Robert M. Pirsig. (Zen and the Art of Motorcycle Maintenance)