Another transmission question

[Jeff Kaplan]

Sedona Sunset has M25 Universal with Hurst 50 trans. So far the boat has been running great. Went out today, always motor from mooring about a mile out into channel. After a few moments of motoring, felt a clunk, as if I ran over a lobster bouy, but not. Could still motor, but if rev's brought over 1500, boat shook like it was coming apart. Checked t fluid, up to level, no trans leaks, in neutral, engine purred, so something went a foul in the transmission.  Looking to get any info, help if any one has experienced this. Thanks in advance...Jeff

[Noah]

Maybe it is not your transmission? Have you checked you prop? Engine mounts?

[Jeff Kaplan]

prop was fine when I launched, motor mounts ok. I did forget to mention that shifting into forward and reverse no problem. The clunk I felt indicates something in the tranny.

[Bill Shreeves]

Maybe the prop hit something and shear the key or keyway?

[Bill Shreeves]

Meant to include damage the prop slightly so it can't go above 1500.

[Noah]

After a few moments of motoring, felt a clunk, as if I ran over a lobster bouy, but not. Could still motor, but if rev's brought over 1500, boat shook like it was coming apart.

How do you know you didn't hit something and damage the prop, strut, and or have a gross motor mount/alignment problem or other failure once underway? Just spitballing here—I am not a mechanic. Could be gearbox, but?

[Jon W]

Did you run through any kelp beds?

[Jeff Kaplan]

Definitely did not hit anything. Boat has been running great up till now. Just to be sure, I will dive under boat to check prop. I do have forward and reverse propulsion, but the prop would not create the clunk felt while motoring, indicates a trans issue. Please keep the responses coming.

[KWKloeber]

The tranny damper plate self destructing.....   SPROING.
Can you hear springs being tossed about?  Listen with a mechanics stethoscope?

[Bill Shreeves]

Definitely did not hit anything. Boat has been running great up till now. Just to be sure, I will dive under boat to check prop. I do have forward and reverse propulsion, but the prop would not create the clunk felt while motoring, indicates a trans issue. Please keep the responses coming.

Some additional detail would be helpful.  Did you hear a "clunk" once when the event happened or, do you still hear unexpected noises in addition to the vibration?

If you continue to hear unexpected noises, what, where and under what conditions would be helpful.

BTW, if the damper plate is self destructing as Ken is suggesting to consider, you may hear noise with engine running and the gear box in neutral and maybe additional noise from simply putting it in to gear putting pressure on the damper plate.  If the "event" is the only time your hearing anything unusual under 1500 rpm its likely something out of true in front of or behind the gearbox.

I think this test will help to determine if the prop and shaft are the cause.  If you can test again going above 1500 RPM use the gearbox ratio to help with diagnosing.  Your gearbox ratio is roughly: Fwd 2-1 and Rev 1-1.  Being able to run higher engine RPM in reverse, compared to fwd, before experiencing vibration suggests it's the prop & shaft.  Diving under the boat for a visual inspection may only reveal the most obvious damage but, you could look and feel for damage on the leading edges of the blades.

Also, I sail in the Chesapeake where there's little visibility more than a foot or two deep.  I'd never know for certain that my prop didn't hit something even if I didn't see anything floating.  Plenty of fish pots out there and it's possible a fisherman had the float line several feet too short and just a few feet below the surface and plenty other debris out there that isn't visible.  We see prop damage on power boats in the area after big storms.

[Ron Hill]

Jeff : I believe that you picked up something on your Prop and it's setting up a imbalance!!  Go swimming and check!!

I once picked up the plastic wrap from a case of bottled water!!  It did the same thing.  Was a Bit_h to get off because I had to motor in to an anchorage and that plastic tried to melt itself around the prop, strut and shaft!!   

A thought 

[Jeff Kaplan]

Bill, I only

felt the clunk once, no engine noise out of the ordinary. Checked shaft and gear box while motoring, spinning free, no unusual  noise, engine purrs in neutral. I will dive under the boat tomorrow, today too cool and ocean rough. Maybe I did hit a submerged pot, don't know. I'll post again once I see whats under the boat, I hope that's it as I really don't want to pull boat and have trans serviced. We'll see. Thanks for all the replys. Just a quick note, the prop is a composite material, 2 blade, not  brass, came with the boat.

[Noah]

Composite is a good clue. Sounds like a Kiwi Prop. Their blades are "sacrificial" and designed to break if you hit something. Replacements cost about $120 ea. A broken blade will really screw-up your performance and shake things up. First thing to check before you go any further on transmission hypothesis.

[glennd3]

I am with Noah. Hopefully it did what it was supposed to do and saved the trans!

Composite is a good clue. Sounds like a Kiwi Prop. Their blades are "sacrificial" and designed to break if you hit something. Replacements cost about $120 ea. A broken blade will really screw-up your performance and shake things up. First thing to check before you go any further on transmission hypothesis.

[Bill Shreeves]

One clunk and a composite prop?  Yeah, I'm with Noah and I wouldn't perform the fwd vs reverse test I suggested.  If your left with one blade and have that much imbalance you don't want to fracture the remaining blade and have it hit the hull.