Drive System Alignment and Replacing the engine mounts

Aligning the engine for Vibration & Noise led to replacing engine mounts and a broken exhaust riser

A professional project that did NOT go well

October 7, 2011

A trip to the boatyard for bottom paint led to one of those "might as well" experiences.

Prop shaft sitting low in the the log
The prop shaft is very close to the shaft logs' lower edge

An inspection showed that where the shaft enters the boat it was very close to the log's lower edge, wasn't centered, and may be responsible for vibration or noise as the engine moves slightly on its rubber mounting blocks. The fix was to literally raise the engine (about 1/8 to 3/16 of an inch) on its adjustable mounts and re-align the shaft at the engine to propeller shaft couplings.

Well, shoot - the vibration on the boat has always been a problem and one of my near-future projects was to replace the exhaust riser and use a hump hose to help with vibration noise. Might as well have the engine mounts adjusted now while the boat is out of the water! Barring any problems this should take about 3 hours.

Pedro hose is OK
The Pedro Hose looks fine. The camera wide angle lens makes the shaft look a bit bent

I expected problems - the one I had in mind was that one or more of the engine mounts would have to be replaced. If a mount was broken, or the threads seized so it couldn't be adjusted, they would have to be replaced.

The problem I didn't think about was - if the engine is raised up or down without disconnecting the exhaust riser, the riser is going to break. On Reality Check, the immovable riser was connected to the aqua lift muffler with stiff exhaust hose, and this stuff doesn't have any flex.

The good news was - I had all engine mounts replaced. The bad news was - I had to move the start date of the "Replace the Exhaust Riser" project up from spring to IMMEDIATELY.

Was aligning the engine a waste of time and money?

After the alignment I read an article on The alignment might have been just a waste of time and money. Plus I'll never know if the alignment truly helped with the vibration because I HAD to add another vibration reducing piece after the alignment in order to use the boat because the exhaust riser was now broken. The other vibration reducing piece? The fexible silicon hump hose to connect the riser to the aqua lift muffler - part of the Building a new exhaust riser project.

Original equipment engine mounts 1984 Catalina 36 sailboat
The original engine mounts

Lessons Learned

  1. Don't let anyone touch your engine! Seriously, I wouldn't have tackled replacing the engine mounts myself - but if you do, or if you have it done by the professionals like I did - make sure to disconnect your exhaust riser!
  2. To get the best access to the starboard rear engine mount take off the front teak panel and take out the back shelf.

Photos of the prop, shaft, old engine mounts and the new engine mounts.

Removing the front panel and back shelf to get to the exhaust system and starboard rear motor mount.

new starboard engine dampening mount
New engine mount, front starboard mount

Parts & Labor

  • Labor - loosen and adjust engine mounts - 3 hours
  • Labor - replace engine mounts - 1 hour each
  • 4 engine dampening mounts - $45.00 each
exhaust riser broke
Exhaust riser broke

How do other people change their engine mounts?

Here's some links to some successful projects on changing engine mounts FAQ page on changing engine mounts
Sail Donnybrook blog, changing engine mounts on a Catalina 34 - Drive System Alignment
Maincruising "How To" page on replacing motor mounts


Universal M25 Diesel

Heat Exchanger

Engine Compartment Insulation / Soundproofing

Anchor Locker





Bimini for the Boat



Edson Pedestal Controls