I am having a discussion with a friend about an engine.

If you look into the back of an engine, the connecting rod is exposed and the

top of the piston can be seen. IF you rotate the engine over so the crank

puts the piston at TDC, I would estimate there is about enough movement

to move the connecting rod from 11:00 to 1:00 without bring the piston

down. For the sake of being a little closer, lets say from 11:30 to 12:30,

there is movement in the connecting rod.

Is this something I should worry about, or should I change it??

Also, should I be able to rotate the engine by a finger by moving the

connecting rod with a glow plug in it??

What are your thoughts??

Yeah, I'd have to say that engine is past it's prime. That sounds like a LOT of rod an pin play to me.
I'd say time for a rebuild, p/s/r and maybe a crank, depending on if the pin is too outta spec.

rod slop..crankpin and rod are worn out also with the loss of compression your better off replacing the engine,otherwise you will need a new rod,crankshaft,a piston/sleeve pinch service and prob new bearings.

A little bit movement without moving the piston is normal but not as much as you say. Also the turn through the compression by one finger sounds not good.

But the main question is how the engine is running and about which engine are we talking. If the engine runs fine there is almost no need to change things if not you have to compare the prices of all parts and a new engine and these days it is a small investment above the parts to get a new engine.

Well, generally, pinch at the top doesn't mean much to me. I generally am able to take a piston/sleeve/connecting rod out of the engine, put my thumb over the top of the sleeve. Push the piston into the sleeve and when the piston closes the ports, I can feel resistance in the form of pressure. Now, that's not scientific because air will leak out because of the contour of my thumb, but, I feel air should only come out from the top. Not from the sides of the piston. Also, I should at least have some sign of compression.

All engine should seal with some form of compression otherwise, how is the engine able to make power??

Given the engine rotates as such a fast RPM, the compression is brief, but, I think there should be something there.

I also feel when the engine is turned over to TDC, you should not be able to turn the crank where there is a clicking noise which due to the slop in the base of the rod. If this much slop exists, when you run the engine, this pounding will quickly kill the rod and possibly the p/sleeve.