Low RPM Vibration

[TDJ2591]

Since changing to the new SS Honda prop, my motor has develped a vibration that can be felt all over the boat, but only at low RPMs. It goes away around 2,000 RPM.

I put a short 2x3 between the prop and LU to hold the prop when I tightened the prop nut to insert the cotter pin but did have to crank down on the nut to get the pin to line up. I'm pretty certain that I could not have bent the blades during install and the blades all look good (plus I'm not THAT strong!).

Any ideas what might be causing the vibration?

[rancherlee]

First stainless prop you have had on the motor? What type of hub? 4 cylinder 4 strokes are susceptible to a slow speed resonate vibration when using a heavy stainless prop due to only having 4 strong "power" pulses per revolution of the prop, especially props with the square bore hub kits. My old Johnson 70 4 stroke had it with stainless props, my DF140 isn't nearly as bad. Rubber hub props reduce the effect quite a bit, and there are some newer "universal" hub kits designed to reduce the "prop chatter" vibration. Older 2 strokes don't suffer this because they have twice as many weaker "power" pulses per rotation so it's smoother.

[lakerunner]

My 90 E Tec rattles the doors at 900 rpm but smooth at 1100

[TDJ2591]

First stainless prop you have had on the motor? What type of hub? 4 cylinder 4 strokes are susceptible to a slow speed resonate vibration when using a heavy stainless prop due to only having 4 strong "power" pulses per revolution of the prop, especially props with the square bore hub kits. My old Johnson 70 4 stroke had it with stainless props, my DF140 isn't nearly as bad. Rubber hub props reduce the effect quite a bit, and there are some newer "universal" hub kits designed to reduce the "prop chatter" vibration. Older 2 strokes don't suffer this because they have twice as many weaker "power" pulses per rotation so it's smoother.

That's interesting. So this could be considered normal? It is a much, much heavier prop than the composition prop it replaced and is the first SS that I've tried. Prop does not have a interchangeable or separate hub. I've thought of putting the old prop back on it to see if it now vibrates too, but it will likely be springtime before I will be back on the boat. If it were a bent or misaligned blade wouldn't the vibration get worse at higher RPMs?

[RcgTexas]

You don't wanna hear this but I had a prop shaft that was 50 thousandths out on a dial indicator. and had a minimal vibration at low rpm and virtually none at higher rpm. but was visibly out enough to see with the naked eye. check your prop shaft with a dial indicator just to be sure. and yep it was on my 135 Honda new from the shop!

[Stinger 88]

As rancherlee indicates your proplem is also called Clutch Rattle, get the right hub for the prop and alot, not all of the rattle will go away.

[TDJ2591]

You don't wanna hear this but I had a prop shaft that was 50 thousandths out on a dial indicator. and had a minimal vibration at low rpm and virtually none at higher rpm. but was visibly out enough to see with the naked eye. check your prop shaft with a dial indicator just to be sure. and yep it was on my 135 Honda new from the shop!

Thanks Randy. I wonder if I could have bent the shaft tightening down the prop nut. I used one of those yellow plastic nut wrenches. If so, is the only cure to replace the shaft? Cost?

[rancherlee]

It's also a slight chance the rubber hub wasn't perfectly pressed into the prop causing a wobble, which would be visable when spun by hand. Does the vibration only happen at certain low rpms or is it constant all the was up to 2000rpm. Mine was only right at 900 and at 1500rpm on my old Johnson 4 stroke, it was bad enough that it caused a panel of two to rattle but it was only with one specific Turbo Stainless with the hard plastic square bore hub kit. Honda brand props are usually quite good and made by Solas.

[RcgTexas]

You don't wanna hear this but I had a prop shaft that was 50 thousandths out on a dial indicator. and had a minimal vibration at low rpm and virtually none at higher rpm. but was visibly out enough to see with the naked eye. check your prop shaft with a dial indicator just to be sure. and yep it was on my 135 Honda new from the shop!

Thanks Randy. I wonder if I could have bent the shaft tightening down the prop nut. I used one of those yellow plastic nut wrenches. If so, is the only cure to replace the shaft? Cost?

I don't think you could have bent it with a wrench unless you put a cheater on it or you have hulk muscles,

I was told by a dealer to replace it, but my son in law and a mechanic friend tore mine down and straightened it to less than factory specs. No more wobble and all the seals and bearings were in good shape. Time will tell but it shows no signs of problems after a year and half of operation.

[NonHyphenAmerican]

Turn the radio up?

[TDJ2591]

Thanks for all the feedback guys. You've given me some things to check.