You can carefully file a little off the cap to tighten up the clearance a bit.
Use the widest file you can find.
Clamp the cap securely while filing, and try to file the same amount evenly across the flat face of the cap.
Make sure to clean the cap well and reinstall.
If you can turn the crank freely after the cap is tightened on, you are NOT too tight.
Continue until you can feel a slight drag when the cap is tightened on, then add just enough shims for the crankshaft to turn free.
I thought your front plate might be bent.
Thought that was the most likely cause of the broken cap.
Check your rear mounts.
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