This Cannot be Happening! Opinions, please!

[snowrx]

I wonder if the sintered metal could be MIG welded, as in fill the hole with weld to remove the weak spot? My guess is no, but maybe the replacements are made of real metal that could be welded.  Getting it off might be tough later, but not as tough as a cams adrift rebuild.

[Chillidoggy]

A new sprocket is £76. It’s not worth repairing one, unless you’re really stuck. 

[Robert Weber]

$144 US Dollars from JAE. Also replaced the flat washer while I was in there. 

All in all, though I'm not happy that this happened and added to all the work already done, I'm thrilled that I caught this early-on and avoided a catastrophic failure, not to mention the learning that servicing the timing and accessory belts can be done with the engine in place.  Not so sure that I'd try a water pump replacement in-situ, but lifting the engine/transaxle (with the correct equipment) is also a very doable task. 

[snowrx]

Wasn't thinking of a repair, rather reinforcement of existing good part to remove the stress riser effect of the threaded hole by filling it up with weld metal.

[ramjet]

Looking at the first picture, I would suggest that someone has used a puller utilising those holes and has overtightened the puller bolt into the bottom of the hole causing the crack. Under normal use i can't imagine why that pulley would crack along there? No rust on the inside bore to indicate whether the pulley would have been swelling. Does not look age related looking at the rest of the pulley.

Lucky find before it threw a hissy fit. Much like me finding a bad break in the power steering pump casing on my S4. If that had gone, it would have all got sucked into the remaining belts and pulleys and would have been pretty ordinary.

[MrDangerUS]

I bought a billet steel cryo tempered pulley (eBay). Problem solved, I hope!

Always pay attention to the spacer washer at the back. Make sure it is fully seated in the recess of the pulley, no gaps, no "waves".

Often, the pulley cracks when washer is not properly seated and you apply torque to the bolt.

Here is the picture how it suppose NOT to look. There must be NO GAP between pulley and the washer. "Dry fit" first!
 

Chamfering the inner edge of the washer opening helps getting proper engagement during torquing the bolt

 

Edited September 29, 2018 by MrDangerUS