Author: Jeffrey Stack of Chicago Marine Group
Split Shaft Coupler
The ABYC recommends a tolerance of .001 inches or less between the drive shaft and the transmission coupler. I find that most boats I work on are far outside of this recommendation & the pinch bolts are either stripped or broken off inside of the rusty coupler. Removing the shaft from the coupler at this point might involve cutting the coupler with a cut off wheel or in some circumstances, cutting the drive shaft itself. When it comes time to replace the coupler, the only gem I have been able to find in the universe is the split shaft coupler offered by PYI. Their machine shop will even cut a slot for the key. Most often the stock coupler is about the same price as this unique upgrade - the feedback I have gotten from my customers is worth the extra effort and going with this great looking upgrade makes sense for those customers who know the difference between good and fantastic.
R&D Damper Plates
The number one most economical upgrade to the stock drive train is the R&D Damper Plate. I noticed the improvement most on a 35.5 foot 1988 Hunter Legend tricked out of solo sailing. The transmission had never been out of the boat and it was time for a rebuild. Since the transmission was removed, it made perfect sense to upgrade the damper plate to the R&D hammer head. Installation was super easy, the rebuilt transmission mated to it perfectly. Going for a ride around the harbor, I could not believe how much better the boat felt and sounded at idle. You could seriously run the boat at any speed with no vibrations or transmission "clunking". Whenever a transmission is split from the engine, do yourself the favor and get rid of the old style spring damper plate and move to the modern engineered R&D damper plate. You will be super glad you did.
Mounts are mounts, right? WRONG. Switching out engine mounts is never a fun job. Getting a mount that works verses getting the correct one does make a difference. This is the kind of job you do not want to redo, so do it right the first time. Let the pros set you up with the right engine mounts so you can get on with it. Measure twice and order once.
Flexible Shaft Coupling
These should really be standard equipment on all new boats. From a safety standpoint, it just makes sense to add this rather inexpensive isolation unit in-between the transmission and the drive shaft. Slight alignment issues disappear, vibration is dampened, banging from forward to reverse and vice verse happens with a little less bang. If the coupler is going to be split for some reason go the extra yard and install a flexible shaft coupler. I have seen engines in their engine compartment laying on their side because of a line wrapped around the propeller with 38 horse power needing to go somewhere. It is much better to snap the flexible shaft coupler then try to right a sideways engine then replace the drive shaft, and reattach the strut. The flexible shaft coupler makes a bad thing like a line getting wrapped around a prop and service call with the scuba tank instead of a haul out.
For more in depth information on the R&D Marine Flexible Shaft Coupling check out Jason Abrahamsen's blog, "R&D Flexible Shaft Couplings Gets Rid of Vibrations".