Exploding fan pulleys?
I’d lay the blame on the accountants at Citroen, since they were probably the driving force behind the change from the type of pulley which was pressed in several parts, which were then spot welded together before being brazed to the hub.
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So far, in almost 30 years involvement with A series cars, I’ve never known one of that type to fail, (unless you count the one on a 4x4 which was driven through a pond at the International meeting in Yorkshire some years back. Even then, it stayed in one piece, albeit ending up a rather strange shape.)
The type which replaced that design is the one which is prone to fatigue failure, with the cracks always appearing in exactly the same location, where the reinforcement provided by a flange projecting from the hub was omitted.
Worse than that, the method of forming the main part of the pulley is by spinning, rather than pressing. The larger part is then clenched together to retain the smaller section, but there’s no spot welding used to fasten these two parts together and make the assembly more rigid.
Weakening of the parent metal in the heat affected zones resulting from welding the two thin sections to the hub is the last step on the road to failure...
Cross section of typical remains here.
http://farm3.static.flickr.com/2525/4224245301_19c970c9a6_o.jpg Citroen’s introduction of rubber mounted pulleys on the ‘last run’ cars suggests that maybe they’d realised there was a bit of a problem in that area.
In my experience, it’s this poor design which is the root cause of these failures, rather than the chosen method of removal of the pulley from the crankshaft.
Broken or missing fan blades don’t help much either, of course.
Repeated and sustained high rpm will play a large part in finding its weakness, since the load on the pulley increases as the cube of its rpm.
Taking the engine to 6,500 rpm means there’s over 40% more load on the pulley compared to if it’s kept at 5,750, so be warned and make regular checks for signs of the cracks appearing if that’s your preferred driving style.
Hands up anyone who’s had a fan pulley break and be honest about how you usually drive, especially if it's happened more than once...
ken.
