Failed Starter Adapter
I am hoping someone could shed some light on a problem I am having with my (new to me) plane, and it centers around the starter adapter. It is a 1963 Cessna 172D w/3700 hrs TT, 851 SMOH on a Continental O-300-D.
I purchased the plane June 15, 2020. On March 5, 2020 the starter did not engage the engine. The owners sent the starter, and at the request of Aerotech of Louisville, KY, the starter adapter. Aerotech rebuilt the starter adapter and starter. The plane then flew for 32 hours with no problems.
After 6.5 hours of flight time of me owning it, the starter would not engage the engine. I contacted the previous owners to get the back history on why the starter/adapter was rebuilt in Mar 2020, then contacted the mechanic who did the work, and ultimately contacted Aerotech. I sent the starter adapter back to them, and it was so badly messed up that it was not repairable and could not be used to rebuild even. When they saw that, they wanted me to send them the starter, which I did.
They were VERY quick at getting back with me. It was only a day or two before they sent back to me a newly rebuilt starter adapter and my starter that I sent to them. They did not find any problem with the starter. They did not rebuild it.
Not knowing what caused the failure in the first place, we tested the ignition switch. We cycled it a total of 50 times with our volt meter on the ground and the positive wire that attaches to the start position on the solenoid. Each time, 12v was on the line and when we let go of the starter switch, it went to 0. I was sure to not physically move the starter switch back to the both (I've never done that) but to always rely on the switch spring to return itself to the BOTH position. So, we ruled out the starter switch.
Yesterday, the starter adapter and starter were put back on the plane. We did several tests along the way, including manually winding up the starter adapter until the prop began to spin, and releasing as well as feeling what the propeller felt like before the adapter was installed and after the adapter/starter were installed. All was fine.
We then started the aircraft and it was beautiful. We let it run for about 3 minutes, shut it down, and carefully spun the propeller again by hand to compare to our previous spins. All was fine. We started it up again for 3 minutes and repeated. When we spun the propeller by hand this time, the was a definite and loud squeak coming from the engine.
Upon further investigation, we noticed by touch that the Starter Adapter was MUCH, MUCH hotter than the crank case. We could leave our fingers on the case for a few seconds, no more than a brief touch on the starter adapter. We did not have a temp prob to check the actual difference between the two or the exact temp of the starter adapter.
During the run-up, the oil pressure was 50 PSI near instantly, the oil temp moved about a needles width, the ammeter was pretty consistent on 7 AMPS, and the suction was a normal 5.
We then took the starter back off, when we did so, we saw some smoke coming around the bearing. When we took the starter adapter off, we saw more smoke come when pulling it away from the engine.
With the starter adapter now out of the engine, we spun the main gear and there is the squeak. It was very rough and took some force to spin. The main shaft also has black/blue discoloration to it, closest to the clutch.
We are at a loss now. This is starter adapter #2 down. I will be calling Aerotech on Monday, but being #2, it's very concerning. I can understand one fluke of a build, but two?
Is there anything else that we should test/try? Does anyone have any ideas what could cause this? I can't imagine it's the engine, we ruled out the starter switch, the vacuum pump is just a straight passthrough, I don't see how it could affect this. The only thing that I can think of is #1 the starter is the same (although it seems to work just fine, and Aerotech couldn't find anything wrong with it), the switch is the same (we ruled it out), and the engine is the same (don't think that could cause this problem).
Oh, in regards to the engine, it is a smooth running engine! There was not kickback, backfiring, or anything abnormal. Started both times with no more than a single compression stroke, or two.
Please, any thoughts?