B&S Ignition Timing

[KE4AVB]

Maybe that is why I reverse them when I build a new kill harness. I even seen them come with one diode one way and the other the other way. I had a couple new harnesses to give me problems until I started making my own. IF you are grounding the circuit it doesn't make sense to have the diodes blocking the grounding. You want the current to flow to ground to rob (sink) the NPN transistor's base voltage.

Anyway take a break today and go out and enjoy the sunshine and nice weather.

[Arkie]

When his magnetos (several) are going bad and the kill wire is completely isolated I would suspect possibility of external heat or not rule out such just yet especially if he is seeing a red hot exhaust.
With the kill wire completely isolated from other sources and a NEW correct part number non-China clone mag going bad would be suspect of possibility of slow heat build-up.


I've seen a hole burned in the top of auto pistons and also seen the AUTO engines run excessively hot from being out of time.

He indicates it takes awhile for the mags to fail and electronics (like in these type magnetos) do not like heat.

Kinda hard to believe that the lamination legs on a magneto would get excessively hot with good airflow but if the block was getting excessively hot ????????

and yep, weather is really nice out rtoday, been Turkey hunting this AM and now working on some of them lovely Nikki 2 barrel carbs.

[Skywatcher]

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

[SUKI]

Sky, Here I just chalk it to learning experience to be applied later. Here today and yesterday I was rebuilding three Scag spindles. Kinda learn just to buy a set 8TEN spindles which I ordered this morning and be done with it. First spindle had wore the lower bearing cup completely out, no edge to even get a driver on so it a replacement hub. Second spindle the spindle nut was hard to get off but manage to save it. Just got threw with the third spindle, lost the spindle shaft this time almost didn't the not off. Luckily I kept an old spindle last year which I manage savage the parts from. I all I got about four actually working hours in the three spindle rebuilds.

The problem with the spindle nuts is the threading on the shafts is exposed to everything under the deck when mowing. Even with the 1300 ft-lb impact it was hard to get off as it was like things were cross threaded. Holding the shaft was a problem too. Destroyed two 1/4 keys. Hopefully I won't see another Scag deck this year. I am worn out....by this one.-