Balance shaft sprocket - bad wear

[02BLUR]

What would cause this?

See how big the key slot is? It should be about 1/2 the size. So when the car runs, the sprocket slams back and forth and makes a distinct "clicking" sound, almost like a Ducati.

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[ZachM31]

have you checked the torque on the cranksprocket bolt? if thats fine, make sure the balance shaft belt is properly tensioned, (that is if you have balance shafts) i really can't think of anything else that would cause that groove to get worn out that bad...

 

[02BLUR]

I think I figured it out! I just bought this car a week ago. The records show in October of 2003, $850 dollars of head work, then again in November of 2003, another $850 dollars and this time they did the Timing Belt. I'm 99% sure they had the balance shafts 180 degrees out, so it must have been vibrating pretty bad, but the owner ignored it and just drove it for about 1 year. That caused the gear to slam on the shaft and wear the hell out of it. They must have heard the clanking (that got louder and louder) and also ignored it until about a year ago, when it was so bad, they just parked it and didn't know what to do...The vibration must have gone down a bit with the extra play in the gear, but it made so much noise, they were afraid to drive it...