Alternator Mount Fatigue Failure

Car has now done about 6,400 miles and after the run back from the WSCC Dorset Area spent meeting at the beginning of the month as I put the car in to the garage I noticed a high frequency tapping/rattle but couldn't see anything in particular wrong and it cleared when rev'd above idle.  The following day I took the car into work and after taking the long way home I tried again to locate the source.  Using a screw driver as a stethoscope I tracked it down to the alternator.  I removed the belt and the bearing seemed fine but there was some play down the length of the alternator so I decided to replace it.

I took a couple of photographs of the alternator trying to track down the part number but while trying to source a replacement I came across a light weight Denso 60A replacement for a reasonable price so bought it.  The Denso only weighs 3.0 kgs against the current 5+ kgs however, will need a new mount, rewiring with a 3 way connector and some additional connections plus a new 15mm shaft pulley or 17mm to 15mm adaptor for the pulley.  My intent was to put up with the rattle until I can make the new brackets and then fit the Denso alternator hopefully before Le Mans Classic at the beginning of July.

Once the Denso alternator was delivered and with the weather not looking too good for the next week I removed the old alternator to work out whether I'd be modify the mount or making a new one from scratch.  As I loosened the front lower bolt the whole alternator started to move and I discovered that the rear lower mount had broken - with hindsight you can actually see the broken mount in the original photo this is obviously what was making the rattle so no need to replace the alternator.  Once I had the mount removed it was clear that the failure was fatigue with multiple "lands" within the crack and a stress raiser in the weld.

I contacted Mark at Westfield to see if there was any history of this type of failure and he asked me to post the mount to him.  Once he'd received it he also noticed an issue with the hole within the broken mount lug and thought that it could be a combination of (1) manufacturing defect, (2) incorrect alternator mounting - failed mount too loose, (3) belt being too tight.  Whatever the cause, Mark agreed to replace it under warranty and the replacement arrived in the post the next day. By this time I'd worked out that the Westfield mount couldn't be modified to mount the Denso alternator, a new pulley was going to cost more than I paid for the alternator and Le Mans  Classic was now only just over 2 weeks away.  Eventually I tracked down an adapter to allow the current alternator pulley to be fitted to the Denso alternator and for only £5 however, after numerous attempts I couldn't remove either of the old pulleys.  After posting on the WSCC forum I've now got some ideas of how to go forward but need an impact wrench for most of them.  luckily I was looking for an excuse to by a cordless impact wrench and they had just emailed me a VAT free voucher for this weekend so I ordered a ClarkeCIR220 with a 2nd battery.  With all the issues I decided that I'd refit the old alternator for Le Mans Classic as I'd want time to give the new one a good shakedown before heading over to France and there now wasn't sufficient time and the weather forecast was sun and more sun for the next week or so.

Once the alternator was fitted Tricia and I went out for a Father's Day blat to West Bay for fish and chips then back to Yeovil on the coast road via Abbottsbury, Dorchester, Cerne Abbas and Sherborne - 67 miles in all with no issues and the rattle has disappeared.