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Originally Posted by rjdnyy224
Really informative post 
Just so I'm clear: what caused all this is the timing chain guides, those broken orange pieces in your first post, just broke, right? Why exactly did they break? Because the chain skipped? |
BMW has described the issue as a faulty polycarbonate that the guide was made of. This could have been two things from what I've seen: Either the guide couldn't withstand the heat and caused the chain to skip OR the lack of lubrication on the constant startup from Auto Stop/Start caused it to wear down much quicker, causing it eventually to skip and shatter the guide. The orange pieces are the guides and are like that because that chain went haywire and bashed them to bits.
It's definitely a low % chance of failure based on numbers of failures but I think the unpredictability is what causes it to be so worrisome. Even when we look at detecting it before failure, it's practically 50/50. Some have noticed that loud whine and some have noticed no changes. That may have to do with how/where it wears down. If it's a more consistent wear, maybe you get that loud whine as a result but if it's more anomalous, you just get unlucky when that small area causes the chain to go haywire.
It also mostly seems to be that those with unmodified (and possibly modified, who knows) may not have something to worry about as BMW seems to be mostly cooperative with people. That seems to vary from fronting a large part of the bill to fronting the whole thing. I think the more occurrences we have, the easier it may get for future failures.