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Motor vibration

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Erich_MI

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Hey !!!

Looking for any insights.

Recently grabbed a new 2025 Bennington to replace the old one from 2003.

Came with a Honda 50. Seems to vibrate through the boat. Dealer and Honda rep came out.
They hooked up laptop and checked motor out and all good there. I put in bypass and it’s smooth with gas, so definitely not an engine problem.
Then we went through 5 different props. None of them eliminated the vibration felt throughout boat, some made it absolutely horrible.

Both say they didn’t feel anything. I don’t know if it’s just the way a Honda is, possible lower unit issue under prop load, or just me.

Wondering if anyone else has experienced this or if I’m being fed a bunch of BS as no one wants to deal with a “slight issue”.

Thanks!
 
If changing props didn't affect it and everything else checked out, the obvious answer is bent prop shaft or some other issue in the lower unit.
 
Yup, could be a bent shaft. Is the motor mounted low enough so the prop is not aerated or cavitated?
 
sunedog said:
If changing props didn't affect it and everything else checked out, the obvious answer is bent prop shaft or some other issue in the lower unit.
Click to expand...
Different props definitely had different affects.
I guess that’s to be expected.
Possible if a manufacturer defect of a shaft will cause various vibrations based on different props.
I would think that different props would affect performance only, but I can understand that they may have different “harmonics”.
 
Erich_MI said:
Hey !!!

Looking for any insights.

Recently grabbed a new 2025 Bennington to replace the old one from 2003.

Came with a Honda 50. Seems to vibrate through the boat. Dealer and Honda rep came out.
They hooked up laptop and checked motor out and all good there. I put in bypass and it’s smooth with gas, so definitely not an engine problem.
Then we went through 5 different props. None of them eliminated the vibration felt throughout boat, some made it absolutely horrible.

Both say they didn’t feel anything. I don’t know if it’s just the way a Honda is, possible lower unit issue under prop load, or just me.

Wondering if anyone else has experienced this or if I’m being fed a bunch of BS as no one wants to deal with a “slight issue”.

Thanks!
Click to expand...
Model is Honda BF50D4LRTA if that helps anyone.
Someone on our lake FB page said “newer Hondas are built around gauze pads and ball bearings so extra vibration is to be expected”. I don’t know anything about if this is true or not.
 
sunedog said:
If changing props didn't affect it and everything else checked out, the obvious answer is bent prop shaft or some other issue in the lower unit.
Click to expand...
A bent shaft is perceivable when you rotate the prop by hand. I had one that was obvious but still somewhat usable. Measure runout by noting clearance between a fixed object and the center hub.
 
Thank you. That is a great way to visibility see it.

Question is should I monitor center of prop nut or edge of prop ring(section before the blades)?
I would think even the slightest variation from monitoring this would just be exaggerated by increased RPM’s.
Could explain why it’s so noticeable at 800 to 1500 RPM and then seems to blend in over 2000 RPM’s.
 
Measure eccentricity at the most rearward circular end of the prop. You are trying to determine if you have a bent shaft.
 
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