Rules of Thumb:
- Engine only vibrates excessively in neutral - check your motor mounts.
- Engine also vibrates in gear
- check your alignment.
- Mounts must be completely supported by engine bed
- Mount studs should be perpendicular to the engine center line.
You might consider installing a drive shaft system that incorporates a thrust bearing and/or CV joints (the effects of torque produce thrust and load transfer on the mounts).
The engine must be very precisely aligned to the propeller
shaft. The thrust of the propeller
has to be absorbed by the engine and its mounts.
“Sail Boat Auxiliaries”
- And Why They Don't Last as Long as They Should”
by David Pascoe
”... The Bushings, Inc. Mounts supplied with most diesel installations are just not adequate. There is a new mount out, with which I’m very impressed with the design, and is supplied by Caterpillar on all their engines. Unfortunately, I don’t recall the name of the manufacturer, but you can contact any Cat dealer to find out ...”
Goto: Marine Engines: Sail Boat Auxiliaries at Dockside Reports
”Drive System Alignment”
~ by David Pascoe
”... The most common reason (why Drive Systems Go Out of Line) is that over time, the engine mounts wear or sag ...
... if the mounts are the vertical stud type set in rubber in an aluminum base, these are the kind that are prone to rocking back and forth, particularly with heavy diesel. Check the stud to make sure that its centered in the base with the vessel at rest. If its leaning in any direction, the mount is stressed and the system is out of alignment (see photos above ).
Conduct a back down test. It takes two people to do this, one person operating and one observing the mounts and engine. Observe the point where the engine bracket attaches to the mount. One engine at a time, start from neutral, put the engine in gear and then accelerate hard, up to about 1/2 throttle for several seconds. Stop, then repeat this process in reverse, all the while watching the mounts for movement. Repeat several times. If the engine and mount are moving more than 1/8" in any direction, your mounts are not doing their job of holding the engine in place ...”
Goto: Marine Engines : Drive System Alignment by David Pascoe, Marine Surveyor
Pascoe recommends “Ace Mounts”:
Ace Mountings Co., Inc. Marine