T30 MAKEOVER
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GETTING TO KNOW THE A-BOMB

The engine in Ayacucho is a 30-hp, flathead, gasoline-powered, four-cylinder motor called an Atomic 4, which some have referred to as the A-Bomb. Most people, upon first seeing an Atomic 4, think it must have been designed for a farm tractor or something like it from the forties or fifties. It was in fact designed from the get-go as a marine engine and there were about forty thousand of them made from the late forties to the end of the seventies. About half of them are still in service today and they are an interesting piece of work – very simple and quite reliable with a modest amount of maintenance.

For reasons I can’t understand the PO decided to buy a new boat soon after he spent nearly four grand to get the Atomic 4 on the Tartan rebuilt. It was in need after ingesting a lot of seawater and having practically no power due to the fact that the cam on the crankshaft that pumps the mechanical fuel pump arm was worn nearly round. Before owning the boat I had never paid much attention to the motor, even though I had sailed on the Tartan with the PO for years. It worked and it was his toy. I do remember at one point that the motor looked so rusty that a good swift kick in the side might turn it into a pile of rubble. Incredibly, it looked like new after the rebuild.

After replacing the fuel tank we launched Ayacucho and headed for Maine. As is usually the case on these junkets we motored in calm air all day without a shred of trouble and anchored behind Richmond Island on Cape Elizabeth for the night. The following morning we tried to start the A4 but it just would not fire up – and we had plenty of gas. After trying everything I knew I was getting nowhere, and the batteries were getting low.

Onboard was a manual on the A4 from Moyer Marine. The manual was pretty comprehensive and delved into diagnostics, thankfully. It suggested a simple compression test where you remove the plugs and one by one hold your thumb tightly over each sparkplug hole while someone cranks the engine with the starter. If there is compression there will be a little fart as air pushes past your thumb. If no fart there is no compression. If there is no compression in two adjacent cylinders you have a blown head gasket. If no compression is in say, cylinders 1 and 3 or 2 and 4, you have a stuck valve. We had a stuck valve. But the manual didn’t tell you where to go from there.

So, for the next couple of hours I got to know the engine by removing engine parts and opening up the side of the engine block by way of a removable plate. There were the valve stems and springs. Without getting into the minutia of the fix I finally worked the stuck valve free with a sharpened screwdriver. Everything was back together by two in the afternoon and the very last gasp of the batteries managed to start the engine.

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