Name:	lakngulf -	Reply
Subject:	Serpentine Belt
Date:	6/12/2016 2:22:07 PM

I had to replace serpentine belt on my Mercruiser 5.0 motor.  Replacement seems simple enough and belt tightening without problem.  BUT, when I start the engine the belt around the main motor pulley begins to rise forward over the pulley.  I put it back in the grooves, try tightening more, and then I put back in grooves and try it a bit looser.  Any method and the belt begins to rise forward over the pulley.

You can see the rise at the red arrow.  Also, at the blue arrow the belt moves forward.  Any suggestions?  Second picture is closeup of the rising belt.  It kicks out of the grooves as soon as the engine starts.

Name:	MrHodja -	Reply
Subject:	Serpentine Belt
Date:	6/12/2016 4:06:16 PM

The only thing that comes to mind is that in the replacement process one of the pulleys ended up at an angle to the rest....they all have to be parallel with each other.  An example would be a belt sander....has an adjustmen knob that changes the angle of one roller in relation to the other to keep the belt tracking straight.

Which of the pulleys moves to release tension and allow the belt to be changed?  Alternator?  For S&Gs check its alignment with the others.

Finally, maybe it is a bad belt?

Name:	lakngulf -	Reply
Subject:	Serpentine Belt
Date:	6/12/2016 4:44:13 PM

I agree with your line of thinking = some pulley is "pulling or pushing" the wrong way.   The only pulley that is loosened in the process is circled in yellow.  It seems to be ok and the two nut process tightens the belt good.  In looking at the whole thing it seems to me that that alternator (in square green) is slightly off.  But I cannot easily see how an adjustment could be made.  So I lean toward calling in the folks who know what they are doing,

Name:	MrHodja -	Reply
Subject:	Serpentine Belt
Date:	6/12/2016 4:47:44 PM

Quietly recite the Serenity Prayer, then call Steve!

Name:	Shortbus -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 9:29:32 AM

I had problems with such, it was the bearings in the idler pully.  Remove belt, check wobble.

Wobble all pulleys and look at all from the side.

Ended up replacing the pulley and belt.  Good for 10 years so far on a 4.3 merc.

Name:	Shortbus -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 9:32:22 AM

I had problems with such, it was the bearings in the idler pulley.  Remove belt, check wobble.

Wobble all pulleys and look at all from the side.

Ended up replacing the pulley and belt.  Good for 10 years so far on a 4.3 merc.

Name:	lakngulf -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 12:42:15 PM

Thanks for the help.  I now seek professional help.

Name:	cobra -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 1:06:53 PM

Replace the Tensioner :) 

Name:	lakngulf -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 7:29:35 PM

Which one is that?  The smooth one?

Name:	cobra -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 11:22:36 PM

Looking at your picture it looks like the one you have a yellow circle around.   These are preset at factory but over time they lose the ability to keep the belt tight.

Name:	cobra -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 11:33:53 PM

https://www.youtube.com/watch?v=6QrTX0-pz7U

Name:	cobra -	Reply
Subject:	Serpentine Belt
Date:	6/13/2016 11:39:33 PM

• Wipe the entire inner surface of the serpentine belt with a clean rag and examine it for cracks and frayed fiber. You may wish to replace if it looks badly worn or glazed. Loosen the 5/8-inch locking nut on the pulley adjustment stud with an end wrench.

• Unscrew the 5/16 adjusting stud with and end wrench to loosen the belt. If you need to replace the belt, make a note of belt orientation around the other pulleys, or consult your repair manual for their positions. Place the new belt around the pulleys and slip it over them.

• Turn the 5/16 adjusting stud until the belt begins to tighten. Measure the deflection of the belt at its longest travel length between pulleys. Push your thumb lightly against the belt and measure the movement with a ruler. You should have no more than 1/4 inch, or 6 mm deflection.

• Take a more accurate reading with a belt tensioner gauge. Place the gauge hook in the middle of the long part of the belt and pull back on the tool. The gauge needle will measure the pull movement on a scale. Again, no more than 1/4 inch or 6 mm can be allowed. Hold the 5/16 adjusting stud with an end wrench while you tighten the 5/8-inch locking nut with another end wrench.

Name:	CAT BOAT -	Reply
Subject:	Serpentine Belt
Date:	6/18/2016 1:28:19 PM

My 02 cents worth.  Considering the rotation of the engine assembly, it appears that the problem starts at the water pump (circulating pump on the front of the engine.  The one you reffered to as the main one.  (Actually the main one is at the bottom, and is your crankshaft pulley).  Prolly got a bearing going out in the pump itself.  Also, prolly what happened to the other belt.  Hope this help.