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Discussion Starter · #1 ·
Hi guys,

I'm rebuilding the top end of my 73 CL350 and trying to rotate the engine to TDC to properly time the camshaft.

But I'm getting this free play at the top of each piston stroke. There is resistance all the way through the stroke until right around the LT mark and then the crank freely rotates a bit without much effort. Can anyone help me out?

 

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The cam lobes on the opposite cylinder (the one on the exhaust stroke) are transitioning which causes the crank to rotate past TDC. You might find an extra set of hands to hold it in position. Others have used various clamps/vise grips/hydraulic jacks to do the job.
 

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Discussion Starter · #3 · (Edited)
The cam lobes on the opposite cylinder (the one on the exhaust stroke) are transitioning which causes the crank to rotate past TDC. You might find an extra set of hands to hold it in position. Others have used various clamps/vise grips/hydraulic jacks to do the job.
The camshaft isn't installed yet. I'm trying to get the left cylinder to TDC so I can install the camshaft in the correct orientation relative to the crankshaft.

Its just at the very top of the stroke, the piston is moving a barely perceptible amount up to TDC and back down but there's no resistance during this free play at the top of the stroke so it won't stay at TDC
 

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Discussion Starter · #4 ·
Anyone else experiencing this? The resistance of the pistons in the cylinders goes away just at the top of the stroke so I can’t keep cylinder 1 at TDC. The piston falls back down a millimeter (or less) every time.

Any suggestions much appreciated!


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Same applies. You need a method to hold the crankshaft in position at TDC while you install the camshaft.
 

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Since there is not much force acting on the crankshaft with the pistons at the top or bottom of the stroke it is easier for the crak to rotate at these points. I thought for a moment that you might not have the cylinder and head held down tight and that they might be raising up and then pushing the piston down with them, but I do not see it raising in the video. However, for no more then it is moving you should be able to install the cam and line it up. It is hard to get the cam, crank, and sprocket all lined up as you install everything. I install everything and the line them up.
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This is normal. The force during normal rotation is the rings against the liners. At tdc, there is no force as the rods pivot back to forward.

Just make sure the mark is within this area and keep going
 

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Discussion Starter · #8 ·
Awesome. Yeah, TOOLS, I had everything clamped down and it was still sloppy right around TDC for both pistons. Will it tighten up once the cam is installed? I'm just wondering for future tuning such as ignition timing and setting valve clearance, where you have to rotate the crank to a specific point.
 

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You NEVER want it to get tighter. If it did your engine would be destroyed. It is always going to want to move as there are several forces acting upon it. There is compression, valve springs applying force to the cam... When doing things like setting the timing, just learn to deal with it wanting to move.
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