rattling in bell housing lossing power

hello this is my first post and i really need help i have a bayliner 2550 with a volvo penta 260b with a 280 drive my problem is when im under load i am getting a loud rattling in the bellhousing area the louder the noise the less power i have almost till the boat stops apon restarting the boat it hardly wants to turn over (very slow) i took the boat to a local marina and had it looked at guy told me it needed new housing bearings and u joints well i had the work done it took darn near a month guy told me it was not maig the noise ,well if he had did his job by taking the boat out for a test he would of found out that 2,400 later and i still have the same problem if any body has a suggestion on what it could be please let me know thax

Re: rattling in bell housing lossing power

Pull the exhaust elbows and check the condition of the flapper valves, if one has broken off and fallen to the bottom of the Y-pipe it will restrict exhaust flow at larger throttle settings, limiting power and seriously overwork/overheat the motor. The noise may be the flapper rattling around like a leaf in the wind.

If this is the problem you may get lucky using a mechanical 'fingers' to pick the part out of the Y-pipe, otherwise pull the drive and fish the piece out thru the exhaust bellows.

Re: rattling in bell housing lossing power

well thank you for youre help but found nothing,took the boat back to the shop found compression was low in 2 cylinders and one plug was totally burned up these are fairly new plugs the porcalin around the electroid was burned to nothing. im thinking about pulling the motor and repowering with a 300hp 350, thank you

Re: rattling in bell housing lossing power

Can you tell us exactly what spark plugs were installed? The wrong plugs can run too hot, melting the electrode and worse. Who put them in?

How low is the compression and which two cyls? If it is two adjacent cyl's it may be only a blown head gasket, far cheaper to repair than to repower.

The cost effectiveness of a repower 40 HP upgrade is very difficult to justify, the performance difference on that much boat is QUITE small.

You may yet decide to repower, but consider your options, if this engine is repairable relatively cheaply it may be worth more than just using it as a 'core exchange' on a repower. A 260 is a VERY popular motor, you should be able to find a buyer quite easily.