70 hp mercury 3 cyl,knocking after hard hit lower end or powerhead?

bigdaddy

Recruit
Joined
Apr 22, 2002
Messages
1
as described merc 70 3 cyl knocking after hitting concrete mooring 3/4 throttle,bent stainless prop ear in half.took apart lower end and shaft straight.knocking only at 1/2 to 3/4 throttle.im mechanic by trade so can take it apart easily.any help as where to start looking would be appreciated.measured the stroke of the 3 cylinders 2 came up short 30 thousands compared to the others. :( g.w.fitzgerald@worldnet.att.net
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,012
Re: 70 hp mercury 3 cyl,knocking after hard hit lower end or powerhead?

Sounds like that motor Stopped quite Suddenly.... probably bent the crank, rods,???? sounds like you have little left to rebuild, Junk it,+ find another motor...
 

Gold Bear

Petty Officer 1st Class
Joined
Sep 26, 2001
Messages
224
Re: 70 hp mercury 3 cyl,knocking after hard hit lower end or powerhead?

bigdaddy,<br /><br />When the prop stops suddenly, the flywheel (which has a heavy mass/weight) tries to keep turning. I'll bet a dollar to a doughnut that your crankshaft is cracked at the first throw underneath the flywheel.<br /><br />Almost for certain the crankshaft is bent.<br /><br />If you even think about repairs make sure you magna-flux the crankshaft and rods.<br /><br />My two cents, Good Luck<br /><br />Gold Bear
 
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