how to avoid engine vibration?

[Guest]

I have an oday daysailorII and have recently added a Mariner 2.5 outboard engine to it on a bracket that came on the boat. At very slow speed it is fine but if I turn it up at all I experience a very annoying vibration throughout the boat. The engine is new, and There are rubber washers between the hull and the bracket. Is this normal? Is anyone else experiencing this on thier boat? Any suggestions? Thank you

Mark Lawrence (mlarry23-at-yahoo.com)

[Guest]

Mark,

I have an old Johnson 4 HP and the engine is far from silky smooth, yet I've never experienced what you're describing. My mounts have no rubber bushings either. I'd talk to the O/B manufacturer as I bet they get questions such as this often...

Kevin

Kevin Clark (kevin.clark-at-usa.alcatel.com)

[Guest]

Mark, the problem is that your motor has no vibration isolation built into it's mounting clamps. I used to have a 2.3hp Johnson (same motor as your mariner 2.5) and found that it vibrated the boat. However, because mine was clamped directly to the transom, it was not as bad as what you describe. The rubber washers between your bracket and the transom are most likely too soft to help. I'd try harder rubber (or urethane) washers, or just remove the bracket altogether and clamp the motor to the transom with a wooden and/or rubber pad between the clamp-bracket and the transom.

Kevin, your 4 hp outboard has two rubber rings built into the pivots for the mounting clamp to absorb the engine's vibrations, they are around the drive leg where the motor turns to steer or reverse. Also, your 4hp is a 2-cylinder engine, Mark has a 1-cylinder engine and this too makes a difference. I know this because this past Summer I replaced my 2.3hp Johnson with a 4hp Johnson....what a difference! No more vibration when running the engine!

Rod Johnson (rjohnson24-at-juno.com)

[Guest]

I hesitate to add my comment because my experience with engine vibration at higher speed is likely not related to yours. I discovered that my prop hub was broken at the shear pin. At lower speed the broken part of the hub keyed with the shear pin and did not vibrate. At higher speed the shear pin (prior owner had replaced it with a hardened roll pin) would slip past the broken area and vibrate (like crazy). You might check your prop hub.
Good luck!

Calvin Trotter (calvin.g.trotter-at-saint-gobain.com)

[Guest]

Calvin brings up a good point that I missed! Check the propeller, perhaps one of the blades is bent slightly, or is missing a chunk after an encounter with a rock or shoal. The Mariner 2.5 hp (I assume?) has the same shear-pin set up as my 2.3 hp Johnson, and this is something to watch, more than once I hit bottom with my motor and bent the shear-pin without breaking it... the problem was that the pin was bent just enough to virtually lock the prop onto the shaft (Yes, I did remove the cotter pin before trying to remove the prop)! Once I removed the prop, I then had to either unbend the shear-pin, or cut it to remove it.

Rod Johnson (rjohnson24-at-juno.com)