Vibration in Yanmar at 2200 rpm in forward only

[john986]

I have a 1993 Hunter 33.5 with a yanmar 3GM??, I believe it s 28hp. I developed a small vibration at 2200 rpm or above when transmission is in forward gear. The vibration does not exist at full throttle with transmission in neutral or in reverse. Cutlass bearing has very little play, no fishing line or any visible obstruction at prop, shaft looks straight, prop is stock two blade. Any thoughts?? Thanks.

 

[John T1594]

I had a similar problem. Change your prop to a 3-blade, suggest Campbel Sailer prop.

 

[Alan Gomes]

If it's a small vibration at a particular RPM then I wouldn't worry about it. Harmonic vibrations at certain RPMs are not unusual. FWIW, my Yanmar 1GM has some extra vibration at around 2100, which disappears when you go a bit above or below that. If it bothers you then just avoid 2200 rpm.

 

[kloudie1]

Might be time to balance the prop.. The gear rario in reverse is "lower" so the prop does not turn as fast in reverse as in forward.. Check the shaft alignment first.. then remove the prop and have it balanced..

 

[Alan Gomes]

Might be time to balance the prop.. The gear rario in reverse is "lower" so the prop does not turn as fast in reverse as in forward.. Check the shaft alignment first.. then remove the prop and have it balanced..

You're right, Kloudie. I didn't read carefully enough what he said. He said 2200 or above. I don't think it's unusual for there to be some harmonic vibrations at or around particular rpm, but they would disappear above or below that. Sounds as though his is present for anything above 2200, which could point to maybe prop, cutless bearing, or something along those lines.

 

[Michael Davis]

Might be time to balance the prop.. The gear rario in reverse is "lower" so the prop does not turn as fast in reverse as in forward.. Check the shaft alignment first.. then remove the prop and have it balanced..

Balance is important and it doesn’t take much to throw it off at higher RPM . If you’re not a racer I’d investigate a three bladed prop as they balance better and I second a Campbell Sailor.

 

[john986]

Ok Campbell 3 blade prop it is, does anyone know what diameter and pitch?
Thank you.

 

[Alan Gomes]

Ok Campbell 3 blade prop it is, does anyone know what diameter and pitch?
Thank you.

They will figure it out for you. They are an excellent company and will work with you to get it just right. Their prop is great.

 

[john986]

Ok thank you.

 

[Michael Davis]

Kelsey will want to know your boat, motor and transmission ratio and the prop will be custom made to suit.

 

[Benny17441]

All props will require balancing from time to time. A three blade prop will present more drag under sail than a two blade prop. If your criteria is to get rid of a small vibration just balance the prop you have. Everything comes with a tradeoff.

 

[john986]

So another question, I had someone outside this forum suggest that it could be the cone clutch in the forward gear of the transmission, any thoughts on that? Only 425 hours on motor and transmission and I replace the oil annually,

 

[nveater]

Same boat, same engine my annoying vibration is about 2600- stops at 2900- I have the max prop 2 blade feathering prop

 

[Mike Oldak]

my diesel mechanic told me that this was a bad year for algae and that it could unbalance the prop.

 

[JoeWhite]

Check for cracked alternator bracket. Ask me how I know. I had a similar vibrations that became severe until on a long engine sail the bracket broke. I have Universal M35B, I am not sure how Yanmar is built.