Ignition Coils - Mick's Tips 413

By: Mick McCrudden

Date: 26.05.2018

No spark, no go. Mick explains why ignition coils need to be loved

Tens of thousands of volts - all from a tiny cylinder...

If you search a little, you’ll find the inspiration for ignition coils goes back well over a century. In fact, there’s an 1898 patent for an ‘electrical igniter for gas engines’ granted to one Nikola Tesla. Does that name sound familiar? It should.

For those of us with older cars, the type we’re most used to is the old oil-filled cylindrical unit. They generate about 25-30,000 volts to fire the spark plugs.

They don’t like getting hot. So if you absent-mindedly left the ignition on while you were working on a car, you could find oil bubbling out of the top of the coil. Not happy. Here’s a little tip: if you’re putting together an engine bay, don’t be tempted to install the coil upside-down, because if the sealing isn’t spot on, it can end in tears.

To get around the heat issue, we got transformer type coils – the ones that tend to look more boxy with a load of heat-dissipating fins on the surface. These are more robust, though they’re not fond of vibration. You need to rubber mount them, but they are a good replacement.

As well as seeing those changes, we’ve also seen voltages rise on a lot of cars, as high as 45,000 or more. Now the catch for the home mechanic is these systems often stipulate more expensive platinum plugs at around $20 each instead of the usual $5 conventional plugs. Don’t be tempted to get stingy if you’re servicing the car as it won’t run properly without the right plugs.

Next along came the distributor type coils, typically in cars like mid-to-late model Commodores and Falcons. For a six-cylinder engine you’d usually find three of them on board with a transformer underneath. Again, vibration is what tends to get them.

Most recently we’ve seen the most controversial of the lot, the modern transformer coil or direct-fire ignition, where you have the coil integrated with the spark plug cap. It’s a great idea in theory, but in practice they turned out to be fragile and expensive to replace as a set. Part of the problem was they were buried deep in the engine bay, usually under a cover, and the trapped heat cooked them.

The prices have come down a lot but if one goes you should change them all.

There have been plenty of redesigns over the years, but the old oil-filled coil still does a pretty good job. And here’s a funny thing, the predecessor to much of this, the magneto, is still the preferred system for the world’s top drag cars…

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