496 HO question

[blown65]

One of the HO's in our Daytona did the same thing. They didnt tighten the idler pulley and the bolt backed out and threw the belt on ours also.
The second engine was just fine, quick fix and back on our way. Sounds like that was your issue also. (This happened when we had about 12hrs on the boat)

[Chubby4Life]

Yes, that is the seawater pump. It wont turn by hand all that easily as you are trying to compress the rubber vanes in the pump....Put the belt back on, check for proper tension and watch all the pulleys to see if they are turning and if they are still in line with each other....
Thats great news. I really didn't want to drop 6 bills on a new impelller and housing. I had to grip it pretty hard to get it to spin. The tensioner stud is located on the alternator bracket right? If this is it, it's turned in about 75% so I guess the belt has seen it's best days already.

[OverKill]

Thats great news. I really didn't want to drop 6 bills on a new impelller and housing. I had to grip it pretty hard to get it to spin. The tensioner stud is located on the alternator bracket right? If this is it, it's turned in about 75% so I guess the belt has seen it's best days already.
That is correct the belt is pretty much gone. How many seasons do you have on it. It would also explain your tight steering. I'm guessing you have power steering right? You should have the new belt on pretty snug with only a couple of turns with the tensioner. You should be back on the water in no time at all.

[franky]

The other reason a serp belt would dismount is a frozen accessory. Check both pumps, the alternator and the idler(s) for free movement. If they spin, they are ok. If they don't, that is your cause.
You should have had an alarm about one of those not doing their job, though.
The system is manually tensioned, not spring loaded. It is possible that the belt just finally stretched enough to jump off.
I believe 04 and earlier adjusted the belt tension with the alternator. Later years had a spring loaded tensioner on the upper idler pulley.