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OK so here is the senerio.  It is a Mercruiser, either 305 or 350(not sure which) with an alpha outdrive.  Not sure if anyone here has any ideas.  A couple months ago, we were on the way in and there was a storm chasing us.  I was full throttle for about 30 minutes.  Then it started tapping and chattering.  I backed below 3k rpms and it went away, so I just kept it under that.  Then when we reached the dock it died.  Turned out to be out of gas.  OK so we paddled it up onto the trailer.  Pulled it out.  Figured it had sucked up some water or something from the bottom of the tank. 

Next trip out we filled it up with 93 octane, and went fishing.  There was an obvious tapping.  Seems to come and go.  Been on the water many times since.  The tapping is there all the time.  Yesterday coming home from the Glen it got really bad. 

The noise is coming from the rear of the engine.  We cant definitively tell what side it is coming from or if its centered or ??? 

Here is what we have done so far.  I pulled the rockers and pushrods, because the noise sounds just like a bent pushrod.  They are all perfectly straight, and I adjusted the valves, which were way out of adjustment.  I pulled the distributor this morning and it is fine as well.  It has used about 1 quart of oil in about 50 or so hours, and its still clean from the oil change in January.  I topped it off this morning. 

The thing is that the engine still runs strong, plenty of oil pressure, temp is sitting about 160, unless I am really on it for a while, but then it only hits about 170 tops.  There is 40psi of oil pressure at idle and about 60-65 on throttle. 

I am completely stumped.  I seriously doubt it is a bottom end issue, but I cant figure out what it is. 

Any Ideas?????