Whining from the engine area during throttle up and belt tension question

[John Kandris]

Good Afternoon Everyone,

Im looking for thoughts or ideas as to what the problem may be.  When we were on the hard the fall we found our propeller was toast so we replaced it.  Same pitch and size but instead of it being a sailor style blade they are a machine pitch blade. 

The new thing is this.  Idle through about 1/4 throttle no noise between 1/2 and 3/4 throttle there is a whining noise 3/4 to wot no noise at all.  No vibration and honestly lots better performance at all throttle ranges.  Truly much better thrust when docking.

Ive checked all the belts and fluids all within range.  the main drive belt is new I replaced it this winter deflects about 1/2 to 3/4 of an inch is that within range?  Also the belt that I got is notched and not continuous like the old one.

Anyone ever seen this before?

If I had hair id be pulling it out 

[KWKloeber]

@JK

You need to isolate from where the noise originates -- you can use a hardwood dowel stick in your ear (putting in the whole dowel sideways doesn't work so well ;-) and put an earplug in the other one.  Or a cheap mechanic's stethoscope from Harbor Freight and sound out everything from the alternator to the engine gear cover to the stringers to the water pump to the shaft/tranny area and hull to see where the whine originates and is being transferred to where.

An alternator can whine pretty loudly -- a bearing that's going bad can do it -- as can a bad coolant pump bearing so you might check those first.

Good luck searching!

The opinion of my WB distributor is the best belt for our engine is a "top cog" (not a bottom cog if that's what you have.) 
Dayco Top Cog belt.  Take your old one and match up the correct size.  Advance Auto carried them but the size may need to be ordered-in.  Better heat dissipation, better contact, less dust, less wear, less squeal, longer life.  What's not to like about that?
If they have a Dayco GOLD Top Cog get that one.

There's a discussion on the 101 topics thread on how to tension the belt -- both by using a tool and "by feel."

[John Kandris]

Outstanding thank you.  Ill scoop up a scope and trace it down. Im going to get a different belt just to be safe.

Will report what I find.

Thanks

[Ron Hill]

John : You mentioned the same pitch, are you sure the diameter is the same?  A larger diameter will give "buffeting" against the hull.  What is a "machine pitch" blade??

A thought

[John Kandris]

Ron,

Yes it is the same pitch.  I went to Murphy's Propeller in Norfolk, Va and talked to them about it and ordered the new prop from them.  The only real difference between the props is the width of the blades.  This picture is the two props side by side.

The MP supposedly delivers more thrust at low RPM's (docking is way easier) without killing the WOT speed which went up about .5 knot (flat day slack tide)

Im thinking its the tension on the alternator belt, but Ill check that this weekend.

[Ron Hill]

John : WOW! that is really an increase in the blade "cord" !!!

If you are looking at the drive belt - the notches on the top of the belt are for cooling so that is OK. 

Make sure that the drive, water pump and the alternator pullys are aligned. Take a strait edge and put it across the drive pully (on the bottom of the engine) both sides .  It should touch both sides of the alternator pully to be in alignment. Make the same check on the top (water pump) pully.

BTW, what is the pitch on the new and old prop.  It should be stamped on the hub.

A few thoughts

[waughoo]

Though I don't have a solution for you, I have identified props that "sing" at certain RPMs.  I don't recall anymore what the resolution was.  You might contact the prop shop and present to them your range of RPMs that coincide with the sound and see if that have any suggestions.

[Jim Hardesty]

you can use a hardwood dowel stick in your ear

I second Ken's suggestion.  Sometimes the old tricks are the best.  Just be very careful poking sticks around rotating parts.
Jim

[Ron Hill]

Guys : To rid your self of "prop noise"  I've heard that you should file a flat edge on the leading edge.  You don't want that leading edge to be "sharp"!!

A thought