new yami vibrates

[jiffy]

Just bought a new yamaha 115 four stroke on my 1700 pro sport. I love the motor, but have a small issue.

At idle, while in grear, apprx 600 rpm, the boat vibrates to the point where is gets very annoying. Increase the rpms to 900 and it goes away, and stays that way through the rest of rpm range. I had a stainless prop and have switched to an alum to see it was a prop issue, but with very similar results. Never had an issue with my old 90 evinrude on the back. I'm taking it back to the dealer to have them take it out on the water for a test drive. The motor has about 5 hours on it. Any suggestions on what might be causing this?

[propmann]

Prop rattle, you'll really notice it on ss props, you need to switch to a mercury style prop that will that the flo torq 3 hub kit it will take most of the rattle away.

[1625rebel]

Please continue to update on your progress and let us know what the dealer says. I have the same issue with my F75. The vibration transmits to a rattle in my Minnkota trolling motor quick release bracket. At idle speed in neutral it's fine. As soon as I switch into gear at min RPM while trolling is when I get the rattle. That leads me to believe that propman is correct. Otherwise it would rattle when in neutral too, right?

On one of the other boards, someone suggested a bent prop shaft may be the culprit. I haven't checked mine out for this, but my 2008 motor has 15-20 hours on it and has not hit anything, so this seems unlikely.

[Unlogged Eric Olson]

The main reason is the low speed harmonic rom four stroked is much different than that of the 2 strokes.

You can reduce it by going to a 4 blade but when run at the lowest trolling speeds the vibrations will actually loosen bolts and screws all over the boat. Just an observation

Tight Lines
Eric

[TIL]

Prop rattle, you'll really notice it on ss props, you need to switch to a mercury style prop that will that the flo torq 3 hub kit it will take most of the rattle away.



Hit that right on the head, had the same issue with my 75 and this took care of it.

[jiffy]

Boat went to the dealer today. They hope to drop it in the water tomorrow. Keep you posted and what the find.

[Bigiver]

Don't know if will work for you, but I have a Yamaha tiller on my Skeeter 1790. Had a bad vibration at idle when trolling. Tilted motor ever so little so that it moved away from being bottomed out and most all the vibration went away. Also have stainless prop. Let us know what you find out at dealer, Bigiver

[jiffy]

Got the boat back yesterday. Dealer resynchronized the motor and put flo torq lll hub kit with a mercury aluminum prop. Has probably cut the vibration in half. Makes it a little more tolerable, but for the $'s spent on a new motor, I feel it should be perfect.

[staylor]

You've gone from the old 90 hp V-4- a very smooth running 2 stroke- to a 4 stroke that only fires every other revolution- hence the shake. When we all ran 2 strokes you'd get the same issue switching from one of the old Merc in-line 4 cylinder 40s to a John-Rude 2 cylinder 40. Yamaha could tune the shake out, but the motor mounts would become so soft and flexible that the boat would tend to wander at higher speeds. By going to the Merc hub kit you've eliminated part of the shake, but there is probably not much you can do about the rest. Years back I ran an old 140 V-4 Evinrude, which would idle smooth down to about 500rpm. When I moved up to a V-6 Evinrude I noticed it shook a lot more- even though it had 6 cylinders the 90 degree V-6 could not be balanced as well as the 90 degree V-4. I called OMC, got hold of an engineer and asked him what could be done. His reply was "nothing- you've gone from one of the smoothest running engines we've ever made to one that runs about as smooth as any average motor".
Doug