Alternator belt snapped on new 351 PCM

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   Just purchased an '81 SN with a brand new (May 2012) 351 PCM 330hp motor.  The engine runs AWESOME!  Hole shot is incredible.  I have not opened it up because it only has 5 hours on it and because I'm afraid the boat will literally take off and fly!  (Actually I had my 3 year old with me and he wasnt too thrilled about going 55MPH).  I was cruising the lake for about 15 minutes between idle and 3000 RPM's then pushed her up close to 4000 RPM's and the alternator belt shredded. Any thoughts?  Is this just a simple tension adjustment?  The H2O pump belt is extremely tight, could the belts have been too tight?  

I did feel some cavitation just before the shredding of the belt, but I believe that is just a pitch issue on the prop. As I type that I'm now wondering if the cavitation caused the engine to over-rev and shred the belt.  It ran flawlessly from idle to about 3500RPM's. It has an old OJ on it and I was dying for a reason to go to a CNC'd prop anyways.

Thanks Guys!

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MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Topic: Alternator belt snapped on new 351 PCM Posted: July-08-2012 at 7:26pm
	Just purchased an '81 SN with a brand new (May 2012) 351 PCM 330hp motor. The engine runs AWESOME! Hole shot is incredible. I have not opened it up because it only has 5 hours on it and because I'm afraid the boat will literally take off and fly! (Actually I had my 3 year old with me and he wasnt too thrilled about going 55MPH). I was cruising the lake for about 15 minutes between idle and 3000 RPM's then pushed her up close to 4000 RPM's and the alternator belt shredded. Any thoughts? Is this just a simple tension adjustment? The H2O pump belt is extremely tight, could the belts have been too tight? I did feel some cavitation just before the shredding of the belt, but I believe that is just a pitch issue on the prop. As I type that I'm now wondering if the cavitation caused the engine to over-rev and shred the belt. It ran flawlessly from idle to about 3500RPM's. It has an old OJ on it and I was dying for a reason to go to a CNC'd prop anyways. Thanks Guys!

MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 7:34pm


MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 7:36pm


OverMyHead Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: March-14-2008 Location: MN Status: Offline Points: 4861	Post Options Post Reply Quote OverMyHead Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 8:10pm
	Good looking boat. I am not the most experienced with this but its Sunday and I am not on my boat so I will try. Put a yard stick across the faces of the pulleys. All pulleys on the same belt should all be on the same plane. If one is tipped or out of line you may need to shim whatever it is attached to.
	For thousands of years men have felt the irresistible urge to go to sea, and many of them died. Things got better after they invented boats. 1987 Ski Nautique

MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 8:12pm
	Going out to do it now. Thanks OMH!

MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 8:24pm
	All on the same plane. Belt failure? Cavitation+new belt=snap? Belts too tight? Need to adjust the placement of the alternator? I cant find anything on this in the forums collection. Thanks for your help

OverMyHead Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: March-14-2008 Location: MN Status: Offline Points: 4861	Post Options Post Reply Quote OverMyHead Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 8:38pm
	That was my best shot, maybe too tight, I would bet against cavitation unless someone forgot to bolt the motor mounts. Maybe just a bad belt? Put a new one on, it should be taught but still able to deflect about 1/2 inch with moderate effort. Carry a spare, open the box now and then and see what happens. They are easy to swap on the water.
	For thousands of years men have felt the irresistible urge to go to sea, and many of them died. Things got better after they invented boats. 1987 Ski Nautique

OverMyHead Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: March-14-2008 Location: MN Status: Offline Points: 4861	Post Options Post Reply Quote OverMyHead Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 8:41pm
	Never mind the motor mounts, the belts would move with the engine.
	For thousands of years men have felt the irresistible urge to go to sea, and many of them died. Things got better after they invented boats. 1987 Ski Nautique

OverMyHead Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: March-14-2008 Location: MN Status: Offline Points: 4861	Post Options Post Reply Quote OverMyHead Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 8:43pm
	You might want to lighten up the water pump belt just a touch.
	For thousands of years men have felt the irresistible urge to go to sea, and many of them died. Things got better after they invented boats. 1987 Ski Nautique

MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 8:47pm
	I have about 1/16" of wiggle on the WP belt....its super tight. Do belts generally fail? I have not heard of this happening too often, especially on basically a brand new engine. Easy to fix, hard to find parts on Sunday afternoon in Western NY. Thanks for your help and the compliment on the boat. Great story behind how I got it. Guy forgot to add a reserve on an eBay auction = I get $8,000 boat for $4,000. Incredible!!

OverMyHead Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: March-14-2008 Location: MN Status: Offline Points: 4861	Post Options Post Reply Quote OverMyHead Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 9:03pm
	1/16th is tighter than mine. Again I am not a mechanic and am only a few years into my first inboard. Nice deal on the boat. I am jealous.
	For thousands of years men have felt the irresistible urge to go to sea, and many of them died. Things got better after they invented boats. 1987 Ski Nautique

MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 9:30pm
	The guy was nearly in tears. I offered him another $1,000 because fair is fair, but to his credit, he wouldn't take it. Helluva a nice guy......bad eBayer

MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-08-2012 at 9:40pm
	Maybe we'll get a 2nd opinion from one of the other members. I can easily change out the belt, but just wanted to make sure their weren't any other issues to fix 1st. I find it hard to believe that there would be a misalignment issue with a new motor Thanks again

MUCQB Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: June-01-2009 Location: United States Status: Offline Points: 122	Post Options Post Reply Quote MUCQB Report Post Thanks(0) Quote Reply Posted: July-10-2012 at 2:12am
	Anybody have any thoughts on this? I changed the belt out today, but haven't had a chance to test it yet.

Alternator belt snapped on new 351 PCM

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