I'm not really sure what caused this, but I'm glad it happened here in my driveway and not at a cruise-in. I have never had a problem with a Powermaster, but I have always wondered why the gear drive starter manufacturers always thought they could get away without running a nose cone for support. Luckily I had a new stock style starter here to replace it with quickly while I tear this one apart to see if it's worth rebuilding. I don't even know if you can get replacement parts for these? Has anyone else here had the same problem with a known cause? My only guess is one too many pumps on the gas pedal during the cold start up.
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Wow!!!! That doesn't look good at all!!!!

 

Why? Don't mean to be critical, I just don't see why you believe pumping the gas pedal could cause the starter housing to crack.

Looks like it was a POS to me, or as though it was installed WAY out of alignment, and the forces on the gear just finally did it in.

I cracked the noses off 2 starters once after having one drop out of a 6.2 diesel block because the PO had stripped the threads and epoxied it in - the holes I spent a full day on my back drilling into the block (good times!) were not perfectly aligned and she'd crack after a couple of starts.
A careful alignment according the the CSM fixed it.

- Eric

 

Or it could be as simple as bad steel tempering in production which cooled too fast and didn't allow enough martensite to develop.

Remember, alot of production is overseas now......and alot of Steel mills here have closed.

OR it could be a few accidental key turns while the motor was running.....

 

Ouch...
I notice the pinion teeth are a bit chewed up. Was it shimmed correctly when it was first installed? If it was not, I figured there should have been a strange noise as a warning sign...

 

There had been no alignment issues with this starter.

It broke as the engine started and immediately stalled.

The thought of too much fuel in the engine was this block has been decked along with the heads, so there is a little less quench area than stock. These starters can spin an engine quickly. If there was a small puddle of fuel on one of the pistons maybe?? I'm just trying to think of a better reason than "it just broke".

 

And I do appreciate the input guys.

Could be a junk casting for sure.