low RPM vibration, new QST5--Help please

[ttugrad]

2007 Larson sei 180 f/s with 3.0 Merc alpha 1
Prop is a QST5 in a 19 pitch

New prop having noticible vibration up to about 2000 RPM, then it smooths out. Put my old ss prop back on and vibration was not present. I am not wanting to damage my outdrive so am concerned about the vibration. Could it be out of balance? Is the vibration normal? Any help greatly appreciated.

 

[robert graham]

Re: low RPM vibration, new QST5--Help please

You wouldn't think a new prop would be out of balance, but who knows?.. Maybe remove prop,rotate it about 180 degrees on the splines, give it a try like that...maybe it helps. Do you have a prop shop anywhere that could double-check balance for you?

 

[ttugrad]

Re: low RPM vibration, new QST5--Help please

I have heard that some cheap props can be out of balance from the get go, but this should not fit in that category. I don't have a shop anywhere near...I would have to ship it to Kansas to even have it checked. The shop said that they would check it for free and rebalance for $40 if needed. All of that is plus shipping both ways. All of that plus the $400+ I paid for the thing is going to **** me off if I end up having to do it.

I could try the repositioning, any other ideas what might be causing?

 

[robert graham]

Re: low RPM vibration, new QST5--Help please

I have heard that some cheap props can be out of balance from the get go, but this should not fit in that category. I don't have a shop anywhere near...I would have to ship it to Kansas to even have it checked. The shop said that they would check it for free and rebalance for $40 if needed. All of that is plus shipping both ways. All of that plus the $400+ I paid for the thing is going to **** me off if I end up having to do it.

I could try the repositioning, any other ideas what might be causing?

Well if the new one vibrates and the old one doesn't then that says it has to be the prop. Does the new prop fit exactly the same as the old one, with no looseness or end play? You torqued it down the same? I can't imagine a brand new SS prop being out of balance. The repositioning 180 degrees, or even 90 degrees just might help! Good Luck!

 

[QC]

Re: low RPM vibration, new QST5--Help please

I can't imagine a brand new SS prop being out of balance.

Why? New cars break. You can get a bad part for anything out of the box new. Personally I think most prop "balance" issues are blade differences that cause them to vibrate due to shape variations, not weight imbalance. Purely speculation on my part, but bent props always vibrate and they have had no weight changes

 

[robert graham]

Re: low RPM vibration, new QST5--Help please

Well, maybe it is a bad prop from the factory. You'd think the last, most important quality control test they'd run on all props would be balance. May ship it back to manufacturer for a re-check?

 

[ttugrad]

Re: low RPM vibration, new QST5--Help please

So we have established that this is not normal and that the issue is the prop? I could try shipping to manufacturer but I bet if any issues are found they will attribute it to the prop hitting something...it still looks like it came out of the box though. I can't believe that a new prop from Merc would be out of balance from the factory.

 

[ttugrad]

Re: low RPM vibration, new QST5--Help please

I used the same hub kit that I used with no vibration on my old prop, so all should be the same i guess.

 

[ttugrad]

Re: low RPM vibration, new QST5--Help please

One more thought...if it is out of balance, then why does it smooth out at higher RPMs?

 

[QC]

Re: low RPM vibration, new QST5--Help please

So we have established that this is not normal and that the issue is the prop?

Seems logical, but I would not say that it is conclusive if someone's life depended on it . . .

I can't believe that a new prop from Merc would be out of balance from the factory.

I'll ask again. Why?

One more thought...if it is out of balance, then why does it smooth out at higher RPMs?

Well, I think it may be hydrodynamically out of "balance" as opposed to out of weight balance. If so I can imagine that turbulence and higher RPM and a bunch of voodoo stuff that people understand about vibration analysis would come into play and voila, no vibration at high RPM. Also, I can pretty much say that every prop I've ever had seemed to feel different at different points (RPM). Also #2, when I have been forced to run a damaged prop, sometimes they feel better at higher RPM. I dunno, ask a hydrodynamologist . . .

 

[dockwrecker]

Re: low RPM vibration, new QST5--Help please

I dunno, ask a hydrodynamologist . . .

You mean almost all of us wanna be prop gurus by that?

I'm sure this seems silly to have to do on a brand new prop, but as a firm believer that UPS sucks, measure it to see if it somehow got bent in shipping. Pick a point to measure from on your drive that you can rotate the prop and measure the distance to the point of each blade top and bottom. More than 3/16" is going to vibrate like hell. Less than that may be the minor vibe your getting. It's at least worth a quick look.

 

[1980Coronado]

Re: low RPM vibration, new QST5--Help please

Because as the frequncy increases (rpm) the amplitude (what you feel) decreases such that you don't feel it anymore.....but it's still there.

When did you buy it? Have you talked to the supplier? Is there no warranty for defective workmanship?

 

[ttugrad]

Re: low RPM vibration, new QST5--Help please

I only assume that a Merc would be of better quality, given their price and reputation. It is possible to have a lemon Rolls Royce, I consider Merc Props to be at least a well made high end German Luxury car...especially the 5 bladers.

It is not on the boat currently, can I measure using blade tip to blade tip..or perhaps setting a level on 2 blades at a time?

The vibration is not slight, litterally shakes the steering wheel. I am beginning to think that the trip to Kansas is the best thing to do...make absolutely sure and run the 3 blade until I get it back with a clean bill of health.

It pisses me off to say the least

 

[ttugrad]

Re: low RPM vibration, new QST5--Help please

bought it online, forget where but could dig up the receipt. I purchased it at the end of last season, used it on my home lake and was a little concerned. Switched to an aluminum for the last trip of the year to an unfamiliar lake that was down in level as a precaution. To make a long story short...kinda got pushed to the back burner. New season moves it to a higher priority.

 

[ttugrad]

Re: low RPM vibration, new QST5--Help please

Most of the online retailers say that once it is put on the boat is considered a used prop...they have no idea if you put it on and bent it going down the ramp the first time.

 

[dockwrecker]

Re: low RPM vibration, new QST5--Help please

Just set it on a table on it's hub and measure each blade vertically. Top and bottom.