Why when I turn the front wheels by hand, the crankshaft doesn't rotate?

Question

I'm after head gasket replacement and I'm trying to adjust valve clearance.

2 wheels of a fwd 1995 Renault Twingo are lifted off the ground, the engine is in gear, but the crankshaft doesn't turn when I rotate the wheels by hand, What's the problem?

Answer 1

Between the engine and transmission assembly (or part of the transmission assembly) there is a set of gears called the differential. Its purpose is to enable the outside wheel faster rotation when performing a turn.

With both wheels off the ground, turning one of them forward will cause the other to rotate in the reverse direction.

Safely block the rear wheels on the ground and use a jack stand to keep only one wheel elevated. You'll find that you can then rotate the elevated wheel in neutral, and when in gear, you'll be turning the transmission and engine.

For ease of rotation, select the highest forward gear. When you are operating a vehicle with a transmission, the low gears allow high rpm at the engine and a lower rpm and higher torque at the wheels. When rotating the wheel, you are reversing the mechanical advantage, which makes it more difficult to turn the engine.

Selecting the highest gear gives you the mechanical advantage, as best as can be managed.

In my younger years, I would jack up my old VW Beetle and place the transmission in fourth gear, turn on the ignition and spin the wheel to start the engine. Because there was no load on the wheel after starting, the engine would continue to run, although somewhat roughly, until I could pop it into neutral.