Back To Basics

Dodge 12 Valve

Published in the December 2010 Issue December 2010 Build, Cummins

12V CumminsLet's face it. Deep inside all of us, there's a little something that calls to us. It's a practical and simple yearning to simplify and get back to basics. It's this same inner gravity that makes us want to spend time in the wilderness, hunt animals, whittle a stick and use our hands to build things. The same force also makes us want to own a 12-valve Cummins.

The 12-valve Cummins, officially the Cummins 6BT, is the engine at the bottom of the family tree of diesel engines (at least in pickup trucks). Its simple, straightforward design is a symbol of reliability, solid engineering and tractor-style torque. The engine was originally manufactured for use in Case tractors, before it was stuffed into the engine compartment of the Dodge Ram in 1989. Back then the engine came packed with 160 hp and 400 lb-ft. of torque.

Why does the 6BT bring inner peace?

 No electronics. None of those new-fangled semi-conductors on this engine. Just iron, steel and aluminum. It's pretty cool that this engine is self-sufficient enough to run on its own. Just keep the fuel coming and it just keeps running. Dead alternator? No problem. We'll still get home, because the engine doesn't need it. When you do want it to stop, there's an electric solenoid that releases a rod, which disrupts the fuel supply to the engine. If that solenoid goes out, you can turn the key off, but the engine keeps running. If this does happen, you just reach into the engine compartment and push a lever down the old fashioned way and it'll stop. This is simple reliability.

If the battery is completely dead, you can compression (push) start the truck if it's a manual transmission. This is because the 6BT features a mechanical fuel lift pump. If the battery and alternator are completely dead in a 24-valve or common rail engine, you're screwed. On the 12-valve, there are no electronic fuel injectors or injection pumps. No tone ring on the crankshaft to come loose, fall off and tear up your engine. No camshaft position sensors to fail. The 6BT does have a crankshaft position sensor, but not to worry: it's just for the tachometer.

 Fewer moving parts. Fewer parts means less wear and less to break. With 12 valves, rather than 24, the 6BT has 24 fewer moving parts. Twelve- valves and 12 tappets are left out. Of course, as with all Cummins B and ISB engines, the cams are driven directly with gears, not timing chains. This is part of what makes the Cummins such a reliable engine.

 Reliable fuel delivery. The 1st generation of the 6BT (1989-1993) utilized a rotary style Bosch VE injection pump. These pumps are very reliable and provide excellent fuel economy. However, they came from the factory operating close to maximum capacity, so it's difficult to get much over 375 hp out of them. Second generation 6BTs came fitted with an inline Bosch P7100 injection pump, which is a great pump. It was used for commercial applications and came de-tuned from the factory when fitted on the Ram engines. The P7100 pump can be built to supply enough fuel for over 1000 hp. The injectors on 6BT engines are all mechanical. They are spring-loaded and fire when the injection pump pushes fuel to each injector.

 Efficiency. Today's engines are choked down with EPA emissions restrictions. The 12-valve is very efficient, comparably. With lower horsepower and verses their high torque output, common fuel economy in 12-valve trucks is 14-18 mpg in the city and 19-25 on the highway, depending on how the truck is set up.

 Durability. 6BT engines have a better track record than ISB (24-valve and common rail) engines. The 6BT will typically outlast the 24-valve and the 24-valve will usually outlast the common rail engines. The 12-valve uses connecting rods that are made from two pieces of cast steel. The cap of the rod that goes on the bottom of the crankshaft is cast separately from the rest of the rod. The cap combines with the rest of the rod and is assembled with bolts.

Common rail engines use what is called a "split rod" design, where the rod and cap are cast as one piece. After the casting is complete, they break the cap from the rod so it can be installed on the crankshaft. These new rods use less metal and are thinner than the 12- and 24-valve rods, especially around where the rod connects to the crankshaft. Over time, the rod stretches where it connects to the crankshaft and allows the rod bearing to spin and cause catastrophic engine failure. Cummins went to the split rod design to lighten the rotating assembly so it could achieve higher rpms. We should also note that all of the points about the 6BT we've discussed in this article promote longer, more reliable engine service life. The term "million mile engine" was earned originally by the 6BT. We would not use the same term for the common rail engine.

 Noise.The 12-valve 6BT is significantly quieter than the 24-valve ISB because there are fewer moving parts. We think the 12-valve has a nice smooth diesel clatter when compared to the louder, choppier clatter of the 24-valve engine. Neither the 12- or 24-valve can be called quiet when compared to the refined common rail engines.

These are some of the reasons we like the 12-valve 6BT Cummins.

Our primal, inner man (or woman) desires the 6BT's character traits. Deep down, we want to be more 6BTish in our own way. Simple, reliable, tough as hell.

This is why we've purchased another 12-valve Dodge as a project truck. We picked up a clean1998 Quad Cab, long bed with 225,000 miles. The engine, exhaust and drive train are bone stock. With the transmission on its last leg, we were able to pick this truck up for $4,500. We'll show you each step as we build and test this truck.

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