Briggs 15 HP wont start

I have a craftsman rider with a 15 HP Briggs 28N707. I replaced the connecting rod and reassembled and it wont start. The connecting rod melted onto the crankshaft but the crankshaft was OK and all else was fine. piston was fine and cylinder was OK. rings were OK. I gets spark. It gets gas. It backfires when I crank it. When I turn the flywheel by hand I hear hissing from the cylinder like air escaping? I set the timing gear and cam gear exactly with both markers aligned. Is there another way to set the timing markers? Do I need to position the piston in a particular location before aligning markers? I just aligned the markers and set the valves? Please let me know if you have good ideas.
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You probably have the marks aligned 180 degrees out.
If correct, with the cam gear timing mark and the crank gear timing mark aligned, both valves are closed. If the marks are aligned and a valve is open, you need to remove the camshaft and rotate it 180 degrees.
Have a look here for the procedure to degree a camshaft:
http://www.compgoparts.com/Support/Tutorials/CamshaftDegreeing.asp
John W

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FYI if your exactly 180 degrees out rotate the crankshaft 1 full turn and your marks will line up ( cam makes 1 rotation for crankshaft 2 rotations. so every other rotation of the timing marks show 180 degrees out) Did you have the head off? if so did you reuse old gasket? if so the gasket is shot and leaking? do you have any comprestion? are you sure you got the timing marks right? that is my first thoughts you could be out a couple teeth I would start there.

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Hi thanks for the email. I am trying to understand. I do not have a degree wheel or dial indicator so I am going by sight which is pretty good. However, your message seems to be saying that the alignment marks on the gear and the cam may not necessarily be touching each other. From what I have been told, I always assumed that, the alignment marks simply needed to be adjacent to each other so that they came as close as possible to touching each other. If so, it would be properly aligned. But it seems that you are saying that if a valve is still open when the piston is TDC and the marks are adjacent to each other, there is still a problem and then the cam needs to be rotated 180. That would mean that the mark on the cam would be as far away from the mark on the gra as possible? Am I understanding correctly? This is a revalation to me as I have been toying at this for 6 months and from what I was told, the marks must be adjacent to each other for alignment to occur? I am stumped and perplexed. Please help if you can. I am still at the 3rd grade level here.
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I don't understand what they are saying either... because the cam on a single cylinder engine CAN'T be 180 out. If it was, then the timing marks would be on opposite sides of one another! As long as the marks are aligned, it's in time.
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