Why, when rotating the crank-shaft manually, with the spark-plugs removed, is there still some resistance?

Question

K7M engine (Renault Sandero)

I have recently replaced the timing-belt and tensioner. This is a first time for me, doing this job.

The marks are lining up and I'm about ready to put everything back together. But I have a concern that I'm hoping I can get some clarity on, first.

I'm a bit worried the internals of the engine e.g. valves, pistons or cylinders have been bent out of shape, during the loosening and tightening(with the locking pin in) of the crank-pulley bolt. Because I was expecting the rotation to become much less stiff once I removed the spark-plugs.

I understand there is a compression phase. And at some point in the manual rotation, I can feel the resistance disappears completely. But then - possibly on the compression phase, it becomes what to me is still a little too stiff. I don't think I could rotate it by hand. I would need a wrench to keep rotating it.

Answer 1

If the engine is completely back together with the timing belt on, you will be turning both the crank and the cam shaft. The cam shaft will be opening and closing the valves as you turn the engine over.

The valves have some fairly powerful springs on them to close the valves when the cam doesn’t want the valve open. As you turn the engine over, you will be fighting against the valve springs.

There will be rotational positions of the engine where it will take more force to turn the engine, due to more valves opening than at other other rotational positions, rotation won’t be smooth.

If you have only turned the engine over by hand even with a wrench, then I would say that it would be impossible for you to have bent anything.

Just make sure that after several manual rotations of the engine, that the timing marks still align and that the tensioner is still set correctly.

Using a wrench you should be able to turn the engine over and feel the resistance of the valve springs. There would be a different feeling if there were components hitting each other or were not able to move due to being bent.