the.cern
Permanent resident
Posts: 1494
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« on: 08 August, 2011, 10:28:07 PM » |
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My lovely Appia has been suffering with what I understand is a well known Appia problem, the wobbly dynamo syndrome. This problem is caused by failure of one or both of the alloy dynamo pivot castings. One is part of the timing chain casing and the other section is part of the crankcase. When one of these fails the dynamo is no longer fully supported and demonstrates this with a rather alarming shimmy.
On my car the crankcase casting had failed leaving the dynamo supported only by the chaincase casting resulting in a pivot length of say 15mm instead of the full 35mm (these dimensions are estimated) resulting in a degree of twist in the horizontal plane. My great concern was that this would overload the short length of casting on the chaincase which in turn would fail leaving the dynamo unsupported and flailing around, being unrestrained except by tensioning arm.
Well, I got to it before that scenario was realised, but it was not plain sailing !!!!!!!!
The first attempt at a bracket was fabricated from a piece of 3mm plate, to be attached to two of the bolts connecting the crankcase to the block and bent to provide a support to the pivot bolt immediately at the rear of the fractured casting. All seemed well, I was surprised at the relatively rapidly progress I seemed to be making, and the bracket did its job perfectly, the dynamo was secure and properly supported. Then, as always when things seem to be going too well, the error in design and execution displayed itself (with a sneer !!). The supposedly super, problem solving bracket prevented the dynamo pivoting sufficiently to allow the fan belt to be fitted!!!! In other words, the polite version, it was not fit for purpose !!!!!!! The comment made at the time could not possibly be displayed here.
Having made a total **** up, a second version was attempted to address the problem and .......... quite unbelievably it worked, well it has worked for about ten miles, so I'm quite hopeful.
The photos below show the bracket, as stated above, it is secured by two bolts on the crankcase/block interface, then bent downwards, then away from the crankcase to pick up the pivot bolt. The main difficulty I found was in ascertaining the precise location for the hole for the pivot bolt, but time and patience (both running out rapidly) got it done.
I'm not sure that this is the best/easiest way to deal with this problem and it would be interesting to know what other routes have been successfully pursued. Anyway, it looks as though it will do the job so its good enough for me.
In the meantime the bottom of the B20 is slowly but surely being stripped of underseal, but that's another story.
Andy
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