Vibration under power

[steved]

I'm new to this game as a 1st time boat owner and loving my 1977 E32. It has an Atomic 4. The boat has spent it's life on the Great Lakes and is now in Milwaukee. I am NOT a mechanic.

I have a vibration under power that begins to be noticable at about 1,200 RPM. At 2,000 the vibration is seemingly 4-5X the itensity that it is at 1,700-1,800. The engine in neutral seems smooth all the way up to 3,000 which has me thinking that the issue might be related to the prop or the shaft. However, the prop doesn't have a single nick in it, the shaft appears straight, and the cutlass bearing is solid and without play. It also seems that there is a knocking type noise associated with the vibration. The engine mounts appear to be solid and tight.

As I very slowly raise the RPMs from 1,800, at about 2,200 the engine quickly races up to 2,600, 2,700, and it's seems like the prop or shaft are just slipping at that point. I immediately back down. This condition seems to be easy to reproduce and is a consistent reaction.

Are the two conditions, the vibration and the seeming slip of the shaft or prop separate issues? How do I begin to sort this out? I'm not mechanical but love putsing and learning new things.

The boat came with Don's Manual for which I am grateful. But, again, not being mechanical, it could take me a year to even begin to figure out where to look and what to check. I could use some pointers and pointing in logical directions. THANKS!!!

[Don Moyer]

Steved,

Your vibration and the fact that your forward clutch assembly slips at higher power settings are almost surely two separate issues. I'm attaching a more recent set of instructions for adjusting your reversing gear that has grown a few legs since publishing our service and overhaul manual, which may assist you in sorting through the procedure. Your forward adjusting collar is probably only one notch away from where it should be. You could almost make an arbitrary one-notch adjustment on the collar in a clockwise direction (as if you were standing behind the engine looking forward).

Please heed the caution note in the instructions to be careful that the tip of the retaining bolt lines up with the next notch and is not pressing on the outer edge of the collar when you re-tighten it.

Regarding the vibration, you'll simply have to continue inspecting and measuring things within the drive shaft and related hardware. Since you have already checked the prop shaft and related hardware, I think I'd check the alignment of the engine next. The second attachment should help you in
that exercise.

Don

[gfatula]

It sounds like alignment could be part of your problem. I had to deal with alignment last spring when I replaced my A-4. It was my first A-4 installation. A very capable friend offered me the following suggestion and it worked beautifully. You need to understand that the engine mounts can be adjusted and it is a good idea to make sure they move normally to adjust the alignment. You will uncouple the shaft from the engine. That involves loosening the three coupling bolts so take your time, PB Blaster ill free up almost anything if you give it a little time to work. When the engine is properly aligned the center of rotation of the crank shaft will line up with the center of rotation of the shaft. If it doesn't, the wobble will create a dramatic vibration and can cause other problems.

Here is what I did. With the bolts all free and the shaft uncoupled I held three small pieces of paper between the shaft coupling and the engine's flange at the bolt holes. I slid the shaft up against the engine flange and let the pieces of paper go. I adjusted the engine mounts until all three pieces of paper remained trapped by the shaft coupling when I let them go. It worked! Another KISS solution.

George

[steved]

Don and George,
Thank you for the help. I'll check in after I get a chance to work on the issues. It's been well below zero here in WI, so it may be a couple months before it warms up enough to get at it.

[steved]

Thanks Don and George

The one notch adjustment and engine alignment seem to have done the trick. We've had decent weather without any long hauls on the engine until recently so I wasn't sure if the adjustments took hold until a long run across Lake Michigan a week ago. Thanks again.

[Silver Fox]

Vibration Troubleshooting

We also had a serious vibration issue.

The engine was smooth in neutral, including at higher RPM's. The engine was also smooth in reverse. But once put into forward gear, it shuddered the boat so much it would knock the folded main off the boom.

It felt like it would shake the boat apart in a matter of minutes.

So we looked at all the options, and here is a short troubleshooting guide that I used to identify the potential problems (I am somewhat of a newbie):



(Click here if the image is not showing)

It turned out for us that it was our 2 blade FOLDING PROPELLER. Our boat is a 1974 C&C 27 Mk II, and the prop was worn out so that it would not open smoothly - one blade would open first and that was enough to throw the boat around.

We sent the prop to Martec in California, they said it was beyond fixing due to the electrolysis within, so we bought a new prop from them, and it is like a dream!

When the boat is put into forward now it clunks once as the blades open and then torques perfectly, and has only normal vibration. What a relief!!

Hope this helps someone else out there!
Thanks,
Ralph.