Engine mountings for a gearbox with a down angle

[Howard]

Hi. I am about to mount my engine/gearbox into my boat. The gearbox has a 7 deg down angle. Is it a good idea to drop the attachment point of the engine mount onto the engine by 7 deg as well? My understanding is that this would keep the mounts in shear and stop the prop thrust from lifting the rear of the engine.

[seayou77]

Howard, I'm not an expert on engine installations, and our library has a book written by someone who also is not an expert, so I will share what I can.
The engine should have a spec. sheet identify location of engine mounts. Get a piece of ply wood about the size of your eng.,. mount your engine mounts to ply wood. according to specs. build a 7 degree leg to match the coupling. Now you can take this to the boat and see how its gonna set on the beds and align to the coupling. Check clearances for oil pan, height, etc. Now would be a good time to think about an oil drip pan for under the engine. Hope this helps!

[Gary E]

"The gearbox has a 7 deg down angle. Is it a good idea to drop the attachment point of the engine mount onto the engine by 7 deg as well? "

The 7 deg angle is so that you reduce the height required within the engine compartment. Yes, the thrust will tend to lift the engine, but that is overcome by attachment of the engine mount to the whatever you bolt it to. All engine mounts are in shear, compression and tension, and they also absorb torque no mater if you have a 7 deg engine or not. Mount the engine the best way you can, it will be fine.

[ssor]

I changed the engine and the bed logs in Bietzpadlin. It involved about three hours of actual work and about two days of head scratching, measuring, mock-up making and planning. Each job will be different. Once I had done the engineering then the physical installation went like I new what I was doing. :D

The 7 degree down angle on the transmisson allows the engine to be installed a little closer to level. My propeller shaft angle is 15 degrees. All engines have an angular limit for operation.

[ 03-20-2005, 09:25 AM: Message edited by: ssor ]