Maybe it is because the mechanic prefers to work on the inline 6 vs a V8. I feel the same way. The I6 in the 320 version was the M104, dual overhead cam and 4 valves per cylinder. This engine was the last of the inline 6 produced from a long line of 50 years of development, the 250, 280 engine, the 300 engine and then the 320. The inline configuration is a very smooth running engine and in it's latest versions produced over 220hp. The benefits of the engine is that the lower end never fails, the chain is shorter and is less likely to stretch and doesn't need replaced as often. The engine is easy to work and and a very solid engine.
Teh V6's are good engines as well, they changed the degree angle around to make it smoother and get rid of the balance issues, these engines are nice and smooth and fit better in the new cars with less space under the hood. But in a V configuration you have 2 chains, and 2 heads. Basically an inline engine has the block, and the head on top of it, all the cylinders are in line, in a row from front to back, in a V configuration you have the crank in the middle, the rods up to the pistons 3 pistons on one side and 3 on the other, then to get to the cams you need two chains and two heads on each bank of cylinders on each top of the V configuration, same with a V8 except you have 4 cylinders on each side. I hear a lot of good things about the 500 engine, I don't know a lot about the 420, just there don't seem to be a lot of those around. Check the forum out on the search function and buy what you want. If you want a V8 I would go for the 500, if a 6 cylinder, I would prefer the Inline 320 M104, but those were only until 96. After all it was an inline engine in the 300SL Good luck and happy benzing!

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Brian W. Heitman

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