Rapping at 2400 RPM

[Bill Meyer]

Re: Hunter Legend 37 (88) 3HM35F Yanmar Last year the boat developed a groaning (R.R.R.R.) sound or a laboring sound between 1800 2300 RPM. Over 2300 the groaning either subsided or was not noticeable. The alignment was checked (O.K.) but the sound stayed with the boat. From my description, my mechanic felt it related to clutch cones in the transmission. This transmission does not operate with clutch cones. Earlier this season a rattling sound was added when throttle moved with short movements back/forth at under 2000 RPM. I could also create the same rattling sound when putting pressure on the shaft inside the boat. I have taken the following steps to isolate the problem: 1. No noticeable engine vibration 2. No boat vibration when standing at helm 3. Transmission in neutral at 3500 RPM (boat and engine run smooth) 4. Boat in reverse at 2100 RPM no groaning or rattling 5. Checked the propeller (17x10 RH 2 Blade as per specs) 6. Checked the shaft (1" s/s on the lathe - True) 7. Replaced cutlass bearing 8. Replaced Shaft flange and checked shaft lock bolts 9. Removed transmission for visual check test under load 10.Realigned shaft 11.Checked engine mounts All of the above did nothing to resolve the noise problem! Groaning at 2100 RPM + or - and rattling when moving the throttle forward/back. I am ready to take advice. Can anybody help?

 

[Bill Meyer]

3 Blade Prop - Question

Re: Hunter 37 Rapping - Thank you for your timely reply, Patrick. My next move is to try a 3 Blade Prop. I have 3 inches between the present 17" Diam. Prop and the hull. Recommended space is 15% so an 18" Diam. 3 Blade Prop would just make it. My question, Patrick, is why did you go to an 18" Diam. and what pitch do you have on the replacement prop? Also what motor do you have? Thanks for your help.Bill

 

[Patrick Ewing]

Better late than never

so here are my answers.why did you go to an 18" Diam. I got it at an estate sale and it was the only one available.and what pitch do you have on the replacement prop? 20 degrees right hand pitch.Also what motor do you have?Yanmar 3HM35F - 35 horsepowerSorry to take so long to answer you but I had to look up the info on pitch.Patrick

 

[Kevin L. Woody]

R.R.R.R.

Dear Bill:Thanks for the question. I would assume that the noise has not always been present. This would cause me to think that the noise is a result of a component deteriorating. The fact that the noise only takes place with trans in forward gear and not reverse would cause me to focus on the transmission. One of the items which can cause noise and not a loss of efficiency, when it begins to fail, is the damper plate. Because it can partially fail and still somewhat work, you can experience ranges of rpm’s which will produce noise and others which do not. As a damper plate begins to fail, it allows the running gear components to rattle back and forth between being driven by the engine and fly wheel to trying to drive the engine and flywheel with the inertia of the propeller. Not completely sure that what you are describing and what I’m suggesting, is the real cause but it would seem that you have replaced or confirmed that almost all other components have been checked out. It will be hard to confirm that the damper is your problem without replacing it. I’m not aware of any tests that can take place while system is together which will confirm damper plates integrity. If you check out our web site you will see what a damper plate is www.pyiinc.com It’s located in the R&D section. Hope this helps.Sincerely, Kevin L. Woody

 

[Tony Crimi]

drivetrain rattle

Your problem sounds similar to one we had on our cat. 34. the fact that you can create the rattle by putting pressure on the drive shaft was the clue. When you checked alignment, did you check to see that the shaft was running true in the center of the tube to which your stuffing gland is attached? Normal shaft/engine mount deflection will cause the shaft to hit the tube if it is running to close to either side.