flexplate & starter: issues, broken housing

[Canoe]

The 258 was rebuilt in the fall of 2012.
The old flexplate had three wear spots on it, indicating where the starter gear would engage. So it was replaced.
With it newly installed, sometimes when starting it would "stall" once for around one second, then continue and start.
As it was intermittent, it didn't appear to be an issue, likely a weakening battery to be addressed later.

Once home, the intermittent stall continued. Over time, it got worse (greater pause).
Got worse as the cold set in. Starter gear had issues engaging, and same intermittent "stall" problem.

Wired in a friends truck, as though boosting the battery. Same issue.
Swapped in my spare starter. Fired right up, yet still with the intermittent "stall".

After a week with the spare starter, great starting except for the stall:

• starter stalled
• paused 1.5 seconds
• grinding gear sound for a second
• sounds of starter freely spinning

Pulled the starter and found the half-dome housing on the end broken off, and a tooth missing from the flexplate.

Looking back, I suspect a binding issue with the flexplate, located just after one of the gear engagement points: if a particular point was where it was engaging from, something a short distance further on the flexplate would stall it; but if engaging from either of the other two points, it had enough momentum that it would turn right past that point if the engine hadn't started by then. 

It appears the stress of the binding with the starter drawing current and producing torque broke the housing. As to the original binding, what could cause such binding at a specific spot? A misformed tooth? Bent tooth? Bent flex-plate? etc.?

I intent to pull the plugs and turn it by hand to inspect all teeth and the trueness of the flexplate, but after this mishap, I'm not sure that would be a valid indication of the original binding/stalling.

Dare I throw another starter in there to see if it goes? I figure the worst that can happen is I trash the flexplate more (it needs replacing anyway) and possibly the starter.

[Canoe]

[carnuck]

   Replace the starter. Doublecheck engine timing (too far advanced will cause kickback on startup. Cure is to retard 5-10 degrees and try again)
   If the ignition box is headed south, the motor may misfire (both my previous Eagle wagon and '83 Cherokee did that. Sheared the nose off 3 starters till I figured it out)
   A bent pushrod or collapsed exhaust lifter can cause this as well. The cylinder fills with air/fuel mix and backfires when the cylinder opens.

This is barring a bent flexplate, which you would hear plainly.

[txjeeptx]

Ouch. Picture worth a thousand four letter words. Bad news about that new flexplate is that it probably needs to be replaced with another since it got chewed.

When they installed the transmission, did they(or you) lose the aligning dowels between the engine and bellhousing? Or do you suspect a bent flexplate from trying to "pull" the trans up to the engine without the tabs of the torque converter aligning with the front pump, which binds them apart, and often someone has the wise idea to try to "pull them together" with the transmission bolts, usually winding up with a broken front pump in the trans or a bent flexplate. Back to the aligning pins, they are hollow and two trans to engine bolts pass thru them. Without them, the trans and engine can operate along two different centerlines, which can result in a bent flexplate.

[Canoe]

  Replace the starter. Doublecheck engine timing (too far advanced will cause kickback on startup. Cure is to retard 5-10 degrees and try again)
   If the ignition box is headed south, the motor may misfire (both my previous Eagle wagon and '83 Cherokee did that. Sheared the nose off 3 starters till I figured it out)
   A bent pushrod or collapsed exhaust lifter can cause this as well. The cylinder fills with air/fuel mix and backfires when the cylinder opens.

This is barring a bent flexplate, which you would hear plainly.

Timing was at 7 degrees.
Engine ran fine when installed. Doesn't run quite as well now, but the carb isn't running right and was a known issue.
No misfires. No kickback. I lost a starter on my '81 to kickback when I was playing with the timing.

Just that one spot where the starter was held up if the engine started turning from one of the three starter-gear engagement spots. When I turn the key, if I don't encounter that spot right away, it will turn over fine. If I hadn't pumped the gas pedal three times prior to turning the key, then the engine wouldn't start right away. If I don't encounter that spot right way, then the starter would happily keep turning the engine over and over, even though it had obviously gone by that spot a number of time. If I do encounter that spot upon turning the key, then once it got past that, it turned over normally. It's as though once turning over at "speed" it has enough momentum to get past that one odd spot without stalling the starter.

No noise, except for the starter turning the engine held, straining, until it got past whatever was restraining it, then it quickly started.

You've got me leaning towards a mis-formed, bent or otherwise damaged tooth as the original issue.

[Canoe]

When they installed the transmission, did they(or you) lose the aligning dowels between the engine and bellhousing? Or do you suspect a bent flexplate from trying to "pull" the trans up to the engine without the tabs of the torque converter aligning with the front pump, which binds them apart, and often someone has the wise idea to try to "pull them together" with the transmission bolts, usually winding up with a broken front pump in the trans or a bent flexplate. Back to the aligning pins, they are hollow and two trans to engine bolts pass thru them. Without them, the trans and engine can operate along two different centerlines, which can result in a bent flexplate.

The mechanic was considerably more knowledgeable than me, but from what I do know and the parts I witnessed, he was taking great care with the engine assembly and everything else I saw him working on, be it my vehicle or others. Hard to imagine him not aligning things correctly, but, unfortunately, I wasn't there when the engine was put back in. I don't know if those dowels were in place.

I've noticed no other issues or symptoms except for this pause in turning over. What other symptoms could there be from such a misalignment?