Serpentine belt won't stay on port engine

jpowell

jpowell

Active member
Member
Joined
Sep 7, 2004
RO Number
15168
Messages
351
Fought this all of my short season. 1999 Mercruiser 350 TBI Bravo III. First trip out thump thump thump smoke overheat. Pull engine hatch, belt broke, raw water pump seized pulley at strange angle. Mech replaces raw water pump, alternator that shorted out from flinging water and belt. Next trip 2 hours in belt flings off. Come home last part of trip on one engine. Mech puts belt back on, notes it has stretched some, runs boat in slip. Says all OK. Next time out slings belt 10 minutes in at idle in no wake. Mech replaces belt says all is aligned all pulleys ok. Thought new belt was bad. Made 2 hr trip yesterday all ok. This morning doled 10 min to fuel dock, flung belt again. Any ideas what's going on ?
 
possible the alternator was installed incorrectly, spacers etc.. Align a straight edge across all pulleys to see if one is out of plane.
 
There is a pulley out of plane (not in line) somewhere.
 
Check the stretching pulley, may need to be replaced after a while they wobble a bit
 
As noted, something may not have been put back in correctly. Check the water pump, alternator, and idler pulley while the belt is loose. Try to rotate everything and feel for play both in and out and rocking at an angle. Then compare all of the mounting brackets and washers with the other engine. This is the same engine as mine and I just looked at the alternator pics. Depending on the idler pulley you have, you may have a three piece bracket system and if the brackets were sandwiched on the wrong side of each other, just the thickness of the bracket would be enough to stretch one end of the belt. You can find pics at a site called mercruiserparts dot com. They also sell parts but are not always the cheapest. Also check the raw water pump to make sure washers were not put behind the bracket. That would offset that pulley too. Finally, check all of the pulleys for debris stuck in the groves or excess corrosion.
 
Check the spring-tensioner pulley too.

Their purpose can be defeated by build-up of belt dust so even though the spring tension works up to a point( and appears to be fine , it completely binds up past that tension point and can't take up enough slack as the belt stretches slightly.

Granted this was on a car with serpentine belt, but I once discovered that problem with a tensioner , and about 20 minutes of wrench-moving with and against spring tension with very great difficulty and spraying with Teflon lube freed it up completely and gave it back at least 2x it's just-previous travel- like new again. Worked fine for another 5+ years until sold.

And of course any other pulley wobble should be an obvious clue. If they are otherwise properly lined up in the same plane . Watch the dampener pulley in case there is a broken spring.

Are the pulley grooves clean of rust so they don't grab the belt to long?

Once the belt is reinstalled, how much max deflection do you see when you push at the longest free span?
 
Thanks guys! I'm going down to the boat Wednesday night with a straight edge to check out the alignment. I would have never thought that it could be sonmething as simple as placing washers on the wrong side of a bracket. Ill compare it to the other engine. That's a great idea. Will report progress in a couple of days.
 
I was throwing a serpentine belt on my Jeep after some new brackets and moving a hydraulic pump. I tried to check alignment, but there was always something in the way making it hard to measure. Finally got a dayco laser belt alignment tool. Bingo, problem identified in about ten minutes. Expensive, but after getting stranded on the side of the road with a shredded belt 45 minutes old, seemed not so expensive.
 
Update. Finally fixed. When the initial episode happened, the belt got wrapped around the crank and bent the raw water pump mounting bracket 3/4" towards the front of the engine. Replaced the bracket. Problem solved.
 
quote:
Originally posted by jpowell

Update. Finally fixed. When the initial episode happened, the belt got wrapped around the crank and bent the raw water pump mounting bracket 3/4" towards the front of the engine. Replaced the bracket. Problem solved.

Click to expand...


In the event a new bracket was not available, could the original bracket have been fixed or was 3/4 inch too far gone?
 
Mechanic said it was sprung and would not hold a position, ie flexing.
 
Serpentine belts are an overall improvement, except in one way. They are fairly intolerant to alignment issues. A regular V-belt can take a bit more abuse in this area. Serpentines may not even like being off by an 1/8 if the throw is close enough.
 
You must log in or register to reply here.
Back
Top