When Does The Piston Hit

Just did the timing belt on the '2. Took some extra time to take some pics that might answer how far off the cam can be before contact.

The first two are with the crank at TDC. Moved the cam forward and backward until contact.





Then with the cam locked I moved the crank forward and back.







In the first two one or the other valve is hitting the #4 piston depending on direction of rotation of the cam.

Having trouble visualizing what's happening in the last two. Both #1 valves are closed and the piston is moving down, #4 is moving down, #2 and #3 are moving up but seems like they would be pretty low in their bores to be hitting anything.

Well, many of us (Jimbote, Oilhammer, to mention a couple) know what you have demonstrated.

The cam can be slow at least one notch or fast one notch and never cause a problem as far as piston to valve contact (exhaust valve to be exact) and more obviously.

However, each setting has it's advantage and disadvantage.

If I remember correctly, slow cam timing provides better top-end power and fast cam timing will give better low-end power. So, to be safe and definitely in the ball park of optimum operation, the cam should be set dead-on.

Idunno. Gonna have to get out a protractor and count the teeth on the cam sprocket. That looks mighty close.

Still not sure what was going on when I moved the crank. If I had thought it through I wouldn't have bothered since the piston (#4) would be moving down and not hit.

I remember several years ago doing a TB job on a NB. After I turned the engine over two complete turns, TDC on the crankshaft was barely visible at the edge of the view hole. I re-set the thing at least three times before I got it right. There was never any valve to piston contact when I rotated the engine.

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