N231BN

Rich, They certainly do, the cooling fin design is slightly different on a 985 as well. The biggest tell on that picture is the push rod tubes. On a 985 they attach to the nose case where on a 1340 they attach to the power section. Sorry for going all geek mode...

It's harder to tell the difference without the nose case but it sure looks like a R-1340 sump. Beautiful table.

Good points, when he said increasing the voltage to 14.4 extinguished the light I assumed it was a low voltage indication.

All 231's had electric tachs. The first couple of years they still used the alternator to drive the hobbs before they switched to the newer style tach.

Check the wires from the ammeter shunt to the JPI, it is an indication issue.

Here is the schematic for your airplane, I don't have time to look through it right now but I don't think it is on there as it was still a factory option at that time. My '79 uses the "AUX" terminal on the alternator to power the hobbs. If yours is the same there should be a fuse holder in a wire coming from the alternator in the engine compartment. M20K-F3.pdf

The annunciator has it's own adjustment and has nothing to do with the regulator. M20J.pdf

Surefly is in the process of certifying an adapter to use with the Horizon tach. A magneto's P-leads signal is AC, the polarity reverses every time it fires. The signal output of the Surefly is DC positive.

FWIW, I just installed a Surefly on my 231 so I'm not trying to tear them down. I only have one flight on it so far but I was able to run further LOP than before at 15.5k. Fixed timing of course.

There is a lot of valuable information regarding electronic ignition systems and variable timing curves in this thread: https://vansairforce.com/community/showthread.php?t=169923 Keep in mind these guys are using experimental ignition systems that allow them to customize their timing curves but the physics are the same. The takeaway from that thread is the Surefly timing curve is too aggressive for optimal operation. Lycoming was wise to offer "their" units with fixed timing only.

I mentioned earlier in the thread I had repaired a 201 that had a similar failure. I guess it got lost in the chatter about Vaseline... Anyway, the part was original to the airplane. I'm sure I blasted it with plastic beads to get a better look at the failure.

Here is the broken part. It is a "T" extrusion and it looks like the extrusion die left some lines in the part that possibly created a stress riser contributing to the failure. I believe I bought a replacement from LASAR.

Twenty amps will run a lot of modern equipment. These alternators are capable of 40 amps, the regulator blinks a light at you if you exceed 20 amps. I would think it would be an additional bonus to the 231 to add some alternator capability at idle. Give B&C sales a call as well, they can let you know if they have a copy of a 337 for a 231. I installed one on a 182RG(Lycoming) using a field approval from a 182P(Continental) and it was a piece of cake(other than COVID delays at the FAA).

The B&C is a good unit and is fairly easy to get a field approval for. B&C is very good to work with as well. https://bandc.com/product/bc410-standby-alternator-system-for-piper-pa32-cherokee-six-lance-and-saratoga-stc-pma/#controller-regulator

He needs it to drive his King autopilot.