Monday, October 8, 2012

Amazing that it ran: Repairing the ignition advance mechanism

We'll get back to the body and paint soon enough but today we want to talk about the ignition advance mechanism that is housed in the distributor.

First is an explanation of what the mechanism does and why it is necessary. The key piece of information is that fuel burns at exactly the same speed regardless of the engine speed. As such as the engine turns faster and faster the ignition spark needs to be thrown earlier and earlier so that optimum combustion takes place when the piston is at the top of its stroke. Modern cars achieve this with electronics and the Dino achieves this with a mechanical mechanism that is made up of weights and springs.

As the engine speed increases, the weights in the mechanism housing are thrown outwards by centrifugal force. The rate at which they are thrown out is adjusted by varying the tension of springs that counteract the force. It is a critical assembly that requires a lot of precision to keep the engine running well. In our car it was a wonder that the car ran at all as the dimensions were horribly off and we found terrible wear. This was certainly the most neglected mechanical assembly on the whole car and it took a whole lot of new parts, welding, and machining to get it assembled factory perfect once again. The next step is to test the advance curve on a distributor machine and we'll be ready to go.

The lesson out of all of this is to occasionally lube and test the advance mechanism on your classic car. If it is not operating properly it can cause a lack of performance at best and at worse severe engine damage.

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