Bad vibration at > 1000 RPM in forward gear

[John Pomije]

I have 10 yr.old Catalina 385 w/400 hrs. Put on new Autoprop in off season.
On first marina departure of season, heard and felt bad chunking that increased in vibration with > rpm. Shaking stopped when transmission put in neutral. Had boat quick hauled, saw nothing wrong with new prop, but replaced with original, functional Michigan fixed blade prop. Cutlass bearing was a little loose, but tech guy said still well inside usable range.
Shaking Problem still continues with old prop installed.
Disconnected prop shaft from back of transmission. Saw no discernible movement in either flange that would suggest misalignment. Ran up engine in forward,neutral, and reverse to ~2500 rpm, but no shaking.
Problem is between engine and prop shaft, since I think I’ve eliminated the propellers.
Standard 40 hp Yanmar 3JH5E, w/KM35P transmission
Ideas, similar problem, solutions please!!! Thanks John P

[Cheechako]

That's a tough one. Looking at the boat on line it appears the shaft isn't likely very long and very well supported. No outside strut etc. I cant think of anything but a failed engine connecting coupling somehow or the shaft got bent from a bad Autoprop issue.....? Does it have a soft engine coupling spacer in there?

Thought of one more thing: A conventional packing gland traps salt water in there. If the boat is stored the deoxygenated water can corrode the shaft fairly quickly causing deep "worm tracks" on the shaft. When it's run again, this tears up the packing and maybe could cause something like that... just a wild guess....

[HeywoodJ]

Broken motor mount? These can be fine when in neutral, gravity reigns, but once you start putting power out the shaft the mounts on one side are in tension and the other side in compression. If the mount has detached somewhere it can show up as vibration in gear.

Not the only cause, but you’ve eliminated many of the common ones.

Other place to look is the transmission itself, but not familiar with yours, so someone else would have to opine.

[skipperpete]

Hi JohnP.
What Cheechako said about shaft corrosion is very true, it happened to a Dufour I once bought and “wormtracks” barely covers what had happened to that shaft inside the bearings. I also agree with the suggestion that the drive plate or engine mounts could cause the problem but because this problem was non existent before the prop swap it’s worth considering that maybe the key and keyway are somehow causing the propellers to be badly located on the taper... some keyways are kinda bathtub shaped and rarely cause problems but there is another type that has a “ramp” at the inboard end of the slot and can cause misalignment. Usually its wise to prefit the prop without the key and mark the shaft then refit with the key in place and see if the mark agrees with the previous prop position.
Pete.

[Don C L]

Originally Posted by HeywoodJ

Broken motor mount? These can be fine when in neutral, gravity reigns, but once you start putting power out the shaft the mounts on one side are in tension and the other side in compression. If the mount has detached somewhere it can show up as vibration in gear.

Not the only cause, but you’ve eliminated many of the common ones.

Other place to look is the transmission itself, but not familiar with yours, so someone else would have to opine.

That was my thought too.

[JPA Cate]

^^^^and mine.

Very common cause of horrible vibration.

Ann

[Frankly]

My Autoprop works on those soft Yanmar Mounts. On my third set in 16 years and ready for the fourth. My problem shows up as a resonance at certain speeds. "New mounts or new fillings", your choice. Replace the mounts and the problem goes away for a few years.

Autoprop a great propellor but because of the much greater mass will magnify issues with drive system. You might have actually broken a mount. Rear set would be my first check.

You are going to love Yanmar when you saunter up to the counter and get a new set.

Frankly

[Rumrace]

Engine mounts ?

[wholybee]

Originally Posted by John Pomije

I have 10 yr.old Catalina 385 w/400 hrs. Put on new Autoprop in off season.
On first marina departure of season, heard and felt bad chunking that increased in vibration with > rpm. Shaking stopped when transmission put in neutral. Had boat quick hauled, saw nothing wrong with new prop, but replaced with original, functional Michigan fixed blade prop. Cutlass bearing was a little loose, but tech guy said still well inside usable range.
Shaking Problem still continues with old prop installed.
Disconnected prop shaft from back of transmission. Saw no discernible movement in either flange that would suggest misalignment. Ran up engine in forward,neutral, and reverse to ~2500 rpm, but no shaking.
Problem is between engine and prop shaft, since I think I’ve eliminated the propellers.
Standard 40 hp Yanmar 3JH5E, w/KM35P transmission
Ideas, similar problem, solutions please!!! Thanks John P

You need to measure the alignment with a feeler gauge. You can't tell just by looking. It isn't just that the two shafts line up, but that they are exactly flat with each other. If the motor is turned ever so slightly on the mounts, so the flanges are not perfectly flat, you can get a vibration.

Also, once you have it aligned, you can disconnect the coupling, rotate the shaft 180, and check again. If it is fine in one position, but out in the other, then the shaft might be bent.

It's aligned by adjusting the motor mounts, so since you are touching them, it might be a good idea to just change them, and deal with both possibilities.

[John Pomije]

Engine mounts seem fine. Having mechanic check mounts,shaft alignment and potentially the damper between engine and transmission. Appreciate your suggestions.

[MJH]

Originally Posted by John Pomije

I have 10 yr.old Catalina 385 w/400 hrs. Put on new Autoprop in off season.
On first marina departure of season, heard and felt bad chunking that increased in vibration with > rpm. Shaking stopped when transmission put in neutral. Had boat quick hauled, saw nothing wrong with new prop, but replaced with original, functional Michigan fixed blade prop. Cutlass bearing was a little loose, but tech guy said still well inside usable range.
Shaking Problem still continues with old prop installed.
Disconnected prop shaft from back of transmission. Saw no discernible movement in either flange that would suggest misalignment. Ran up engine in forward,neutral, and reverse to ~2500 rpm, but no shaking.
Problem is between engine and prop shaft, since I think I’ve eliminated the propellers.
Standard 40 hp Yanmar 3JH5E, w/KM35P transmission
Ideas, similar problem, solutions please!!! Thanks John P

You don't say if there was any vibration before mounting the Autoprop.

Check engine mounts and alignment.

[RexSnr]

All info can cause vibrations but I think SkipperPete may be more likely to resolve the problem. I presume all was good before or you would have told us. Your further tests have proven a few are ok. Vibration is when something goes “up and down” as well as “round and round”. A cheap dial indicator can test nearly every component does not have ‘runout’ if boat is out of the water, but since the problem seemed to start after prop replacement, I would drill down on the propeller fixing. If the shaft has no (excessive) runout ahead of the prop, you know the problem is in the prop. We will presume both props SHOULD be ok from your introduction. You can remove the keyway and put a thin coating of bearing blue (from car parts store) inside prop and fit onto shaft, then remove it sgain. It should lay a perfect blue skim all over shaft. If so, you know IT can fit correctly onto the shaft. Then do it all again with your key installed. I agree with Pete that you probably have a woodruff key or a burr on the key or keyway, which isn’t allowing to key to sit fully down and is then forcing the prop up and out (minor bend or deflection) when it is being refitted. Again, the dial indicator should prove this IF you can install it appropriately without the spinning prop sending it into orbit!

[merrja]

Did you do the install? It's also possible that that the yard bent the shaft. You can check next time you haul with a dial indicator and rotating the shaft by hand.

[bil56]

faulty engine mounts
bent drive shaft
poorly balanced or incorrectly mounted blades
blade tip too close to the hull
...

[SouthBaySailor]

Since the original prop also causes vibration I would suggest 2 tests.
1- while in water remove the propeller and test for vibration
2- if vibration is felt, remove all shaft zincs and test
If no vibration then unbalanced propeller