Vibration from power train

[James Goodson]

Greetings to all, I have a 1990 Catalina 28 with an M-20 Universal, which runs great, however when in gear at 1500 to 2700 RPM I get a hard vibration. None when out of gear or less when at lower RPM. Thought it was the coupler, however after checking it seems to be well within the tolerance of .001 to .003 in. The 2 bladed prop looks good, and shaft doesn't appear bent. Any suggestions, comments etc. It also runs 20-30 degrees hotter at the higher RPM.

 

[Tom Soko]

Couple of thoughts...

James,Have you checked the cutlass bearing? If that is worn, it could give you a lot of play in the shaft alignment. After 13-14 years, it's probably due. Also, do you know for sure that the shaft is true? I thought mine was, and when I had it checked by a machine shop, it was not. Instead of messing around with trying to straighten it, I bought a new SS shaft instead. Are your motor mounts secure? If they are loose the engine could move when under load. I'm sure others can come up with more ideas, but these are a few to work on. Good luck.

 

[RonD]

vibes

Most boats will have resonance points at ncertain RPMs. Acoustic energy from the engine, transmission, shaft, etc. couples into the mechanical structure all the time -- you can never achieve perfect isolation. When the natural resonance frequency of the mechanical structure (hull cavities) equals or is a harmonic of that acoustic energy, the sound (aka vibration) is amplified. Make sure the engine mounts are in good condition, as they're designed to dampen much of that energy transfer. Also, check the items mentioned in the previous post. After correcting any drive chain & engine mount problems, you can install sound deadening materials around the engine compartment. "SoundDown" in Marblehead, MA is one company that sells the materials. No guarantee that it'll completely fix the problem though.

 

[Joe DiCianni]

Bad fuel a possibility

On my 1990 C30, I had vibration running at 2000 rpm or higher for a whole season. Had alignment checked, etc. Next spring upon changing filters my fuel was discolored to a cappacino tint. Upon getting my tank & lines flushed, to my suprise, no vibration reoccuring.

 

[Eric14564]

I had loose strut

Did you check the strut? I had a loud vibration only at the higher RPMs. When I hauled the boat, the strut moved slightly from side to side. I had it reglassed (and replaced the cutlass bearing). No more vibration.

 

[John]

Steps & engine cover

I also have a 1990 Catalina 28 with a new M25 and new cutlass bearing. I was having the same problem, but I found that about half of my noise was coming from my steps that sit on the engine cover and some was also coming from the head door. You might try checking these ideas while at the right RPM. Sure cut down on the noise and vibrations on my boat. I’m also designing a new latch down for the engine cover, what is come with is kind a mickey mouse and it vibrates a lot.