B&S Ignition Timing

[Skywatcher]

Greetings All

This one has a fellow mechanic and myself both stumped. Briggs engine on a Stiga articulated mower died last summer, dead coil. Replaced with Stens # 440-433 which lasted 5 minutes and died. Ordered and installed a Briggs # 492341 coil which lasted about 10 hours, so figured there was something back feeding into the coil and killing it. Ordered another new coil which was subbed up to Briggs # 591495.

Took the flywheel off and checked everything under the flywheel and around the engine. Installed a diode into stop wire to eliminate any back feeding from the tractor's electrical system. Reassembled the unit which ran for about 5 hours, then the flywheel key sheared and the timing went right out the window. Replaced flywheel key and torqued bolt to spec. Unit ran for about 10 hours and died, no spark, another dead coil. Ordered new coil, back ordered for 3 months, by which time the machine had been put into winter storage.

Finally got back to the unit this week after bringing it out of winter storage. Installed the new coil, engine now runs but won't rev up and exhaust pipe glows red hot. The only time I've ever seen this before was on a Tecumseh riding mower engine where the crankshaft had slipped in the flywheel retarding the ignition about 20º. Here's where my mind starts running. Last year, I had a B&S Vanguard V-twin come in with one dead coil. A single coil was not available, so a pair of coils had to be ordered which came with a stepped flywheel key to advance the flywheel on the crankshaft. Has there been a service bulletin from Briggs regarding these new coils and possibly a stepped flywheel key to correct the timing. Thanks in advance,

Sky

Engine Information
Make: Briggs & Stratton
Model: 282H07
Type: 0113-E1
Code: 0407287C (might be ZC)

[KE4AVB]

The only service bulletin I found is the one about flywheel shearing keys. APSI 82. That the one where we are to install a steel key and increase the torque to 110 ft-lbs. There were a couple other bulletins unrelated to the problem, Engine flooding crankcase and the change over to RTV on the rocker cover. (Totally unrelated on the flooding as I finally got the service bulletin to download, it was for the 210000 series)

ON the coil make sure it is not rubbing on the flywheel even it is properly gaped at the magnet. I just run into one here where I had to double my normal gaping to clear the flywheel. And I have seen coils to fail because they were rubbing the flywheel.

You might have a lean burn problem caused by the carburetor causing the exhaust over heat.

BTW did those Vanguard coils comes with MS sheet that you might still have around. If so and you can send me a copy of it , I get posted in the Briggs files for future reference.

[38racing]

As a test or experiment you could do what I did with the snowblower engines. I used a timing light to mark spark location and determined tdc with a piston stop and homemade degree wheel and hence found timing (26 btdc). Still a question is whether you lose another coil. Beyond the diode you would have to run with a dedicated kill wire which only led to a ground source for you to kill when necessary.

[Arkie]

You probably know some of this but just some suggestions or thoughts:
With a diode in the kill wire will not prevent the coil from being burned out if for some reason a stray voltage were applied to the kill wire. (the installed diode will not prevent any back feeding of a positive battery voltage from the switch or wire loom) The coil will still draw current thru the diode.
Diodes on the Briggs Intek twins magneto kill wires were used to isolate the two magnetos from each other. (if a hard 12v voltage were to get on the kill wire it will usually melt a coil and also burn out the 1 amp, 1000 PIV diodes. (because the diodes are forward biased)

I would do as 38 racing suggested run a temporary kill wire that can be grounded to the frame to kill or install on a temp mounted Normally open spring loaded toggle switch to kill.
This will isolate the engine Magneto kill wire from the ignition switch and other wiring as a test.

I would think that the RED exhaust is timing and lean condition.
Rather than just watch for a red exhaust I would think about using a IR thermometer and check the temp of the cylinder cooling fins during warm-up. I do not know what the high temp should be for your 4 cycle, but would get concerned if I seen the head/cylinder area going to 350F fast or trying to go above. Excessive heat can cause a piston skirt swelling into the cylinder wall and not a good thing.
I've seen 2 cycles start and idle but not rev up when timing was off due to wrong magneto, (like you mentioned) I would suspect that maybe the NEW type mag is not for that engine.
Also make sure that the crankshaft and flywheel taper are cleaned good with no lube on the taper. A key is normally only for timing so as the flywheel fits onto the crank with correct timing and not to hold the flywheel securely after it's been properly torqued. The machined taper and torque is the intended friction fit to prevent flywheel slippage.

[KE4AVB]

You probably know some of this but just some suggestions or thoughts:
With a diode in the kill wire will not prevent the coil from being burned out if for some reason a stray voltage were applied to the kill wire. (the installed diode will not prevent any back feeding of a positive battery voltage from the switch or wire loom) The coil will still draw current thru the diode.
Diodes on the Briggs Intek twins magneto kill wires were used to isolate the two magnetos from each other. (if a hard 12v voltage were to get on the kill wire it will usually melt a coil and also burn out the 1 amp, 1000 PIV diodes. (because the diodes are forward biased)
I

I think you are a little confused here. IF the anode is connected to the coil and the cathode is the side being grounded via switch no feedback voltage or current should flow other than micro levels. Actually the spec reverse current is only 1 uA on the following diode. You should be able apply up to a +1kV with no ill effects though I don't push these diodes much more 50% of their ratings. Just an engineering thing call safety ratings.


1N4249GP
Vr - Reverse Voltage: 1000 V
If - Forward Current: 1 A
Type: Standard Recovery Rectifiers
Configuration: Single
Vf - Forward Voltage: 1.2 V
Max Surge Current: 25 A
Ir - Reverse Current: 1 uA

Even the 3A 1000piv diodes I use here have only a 10uA reverse current.

1N5408-G
Vr - Reverse Voltage: 1000 V
If - Forward Current: 3 A
Type: Standard Recovery Rectifiers
Configuration: Single
Vf - Forward Voltage: 1 V
Max Surge Current: 200 A
Ir - Reverse Current: 10 uA

[Skywatcher]

Hi Again

The diode I installed is way bigger than necessary, but it was the only diode I had at the time. The diode came from an Oregon # 33-420 replacement charge diode wire to fit a Tecumseh engine, so I believe is rated for 15 amps. The other mechanic with whom I'm working on this issue used to be my service manager when I worked at the John Deere dealership. He went to the same tech school as I did (Southern Alberta Institute of Technology), just a few years earlier, and had the same 4th year instructor for electrical and electronics. We both know what the other is talking about when it comes to this sort of problem. All the best,

Sky

[KE4AVB]

Sky looking at the service manual there is no diode charging system above 3 amps for Tecumseh. Next level which is around 5 amps and up uses a rectifier/regulator setup.

[Skywatcher]

Hi Again KE4

Guess that would make it a 3 amp diode then. I just know that it was larger than the diodes my brother used to use back in the 1970's when he was building his electronic circuitry, but smaller than the ones you'd find in a Niehoff 100 amp alternator. All the best,

Sky

[KE4AVB]

Yes different diodes have different case designs. I got a power supply I built that have a pair 6 amps that the cases are nearly the diameter of the US dime and they get rather hot as they got a lot internal resistance. But I have use the power supply to power my 250 watt PEP SSB RF amplifier that pulls up to 30 amps when I reach the 250 PEP power level and I have never blown them. Even the regulator 2N3055 that I used as a regulator transistor is only rated for 15 amps.

What I need to look up the diodes is the part number from the diodes themselves then I would know exactly what you have in front of you.

[Arkie]

In my post referring to Briggs twin OHV diodes used as isolation, the Cathode is connected to the mag and the anode of each diode connects to the kill switch wire and the diode will be forward biased if a positive voltage is applied to the kill wire the primary of the magnetos are low resistance and a high current would be drawn through the magneto primary. (the diodes on a Briggs twin Intek OHV would not be reverse biased)
You can refer to Ignition section 2 pg 5 of the OHV Briggs Intek service manual to see such.

My main point was to think about doing as 38racing suggested and isolate the kill wire from the ignition switch and the wire loom because using a diode may not prevent a mag burnout depending on how the diode were installed if a intermittent voltage is getting onto the kill wire.

What is the latest direction or thoughts as to why the mags are burning out and the exhaust is red hot?