IF yours is the same problem that I experienced, ( may not be) I will clarify my other response since it will not let me edit the post ,in order to narrow it down, and/or save you the trouble of going through the same thing.

Last Dec as soon as it started getting cold, the 86 240 began making a grinding noise on start up when the key was released, that sounded like the starter not disengaging. Always started, but made noise. The colder it got, the worse it got. Since I had a junk yard starter ready to go in the shed, I went ahead and swapped out starters. No difference, still made the same noise.

I next took the original starter, completely disassembled it, cleaned,re- greased with synthetic grease, re-assembled and bench tested. Tests just fine. Placed in 0 degree freezer overnight ( wife no like) and bench test. Tests fine. Install on car, and it makes noise. Give up and go buy a re-built starter for $100. Install. Still makes noise. Getting damn good at whipping a starter on a 240, about 20 minutes start to finish. Since three different starters did not make any difference, logic should dictate that it must be something else.

I replaced the ignition switch. No difference. Then new wiring between the ign switch and solenoid. Nope. New battery cables and high CCA battery. Nope, still makes the odd noise. Even swapped out the oil for a 5w30 synthetic, which I normally do not use. No difference.

Time to think outside the box, maybe something else on the motor is making the grinding noise, and it just sounds like the starter from inside the car. Used the remote starter hook up/connection on the firewall to engage the starter so I could listen from the engine compartment as it is started. It is the starter making the noise for sure. Well, maybe one of the front belt driven units ( ac comp, ps pump, alternator or water pump )or bearings is bad, and preventing the motor from exceeding the 300 rpm or so necessary to overrun the bendix so it can dis-engage, so I remove all belts the night before and start car in the morning when it is 17 degreesF. No noise. Starts fine. Power steering pump pulley feels like it is spinning in mud it is so hard to turn. Install ps belt, and it makes the noise. Flushed out the old fluid, and all is fine.

It has done it a few times again this year, only because the rack had started leaking and I added some of the Lucas stop leak. It did stop the leak, but thickened the fluid. I went out a few weeks ago and flushed the Lucas out. No noise now, but the leak returned big time. New ps rack for Christmas.
The whole episode may also be an early warning of failure on a 20 year old ps pump. Don't know, but I thinks I will grab one next trip to the junk yard.