Volvo SX drive bogging down -- no plane

[Island Garry]

Hi all. I have an unusual prob that I cannot seem to figure out. I have twin volvo 5.7s with sx drives. the starboard engine/drive boggs down such that I cannot get on a plane -- by this I mean I have to throttle way up on the starboard engine, but the drag or whatever will not let me get above 2900 rpm which is not enough to get me on a plane. The engine sounds fine, runs smooth and has new fuel filters and will throttle up in nuetral -- so I think the engine is OK. It seems as though something is dragging and not delivering the engine power to the prop. I recently had the prop rehubbed. and the problem began intermittently, meaning it was slow to get on a plane and I had to throttle up the engine higher to get the 3200 rpm needed for a plane -- now it will not let me get to the 3200 -- eventually the prop spun out. is it possible that the prop was slipping in some way? if so, I would think that I would overrev like when spinning a prop, but that did not happen. any help would be greatly appreciated. Drive prob? transmission prob? just a bad prop? (the prop is a 15 by 17). Cheers.

 

[Reel Poor]

Re: Volvo SX drive bogging down -- no plane

List of possible causes of low WOT.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation (Full tuneup done recently)
• Remote control cables and linkage for proper travel to open throttle plates fully.

__________________
Don S.

 

[Island Garry]

Re: Volvo SX drive bogging down -- no plane

thanks for the ideas. Most of the items are not it -- blades OK, bottom clean, pitch was fine for last few years so no reason for it to be a prob. New fuel filters, fairly recent tune up but engine runs smooth anyway -- new fuel in the tank and the other engine runs fine. The exhaust flappers I will check as one fell down before and I know volvo suggests taking them out now, but I would think I would see other probs if the flapper was not working such as overheating etc. I have not checked fuel pressure -- any ideas related to the drive or what could cause this in the drive or transmission? Do you think the rehubbed prop could have been "slipping" some how? Cheers. Garry.

 

[Reel Poor]

Re: Volvo SX drive bogging down -- no plane

When was the last time the drives were off and serviced, gimble bearing checked and lubed. Have you checked the drive lube for contamination, water and/or metal debris? Anything is possible but eliminate the most common problems first.