Yamaha Prop trueness

[Halfhitch]

I got an unused Yamaha Saltwater series prop a few days ago. The prop I moved from my old 2004 3.3L motor is a 15 1/4 X 19 and it was too much for the new 4.2 Liter, due, I think, to the difference in final drive ratio. I got a very good deal on a 15 1/4 X 17 since a guy had bought it for his boat several years ago and had health problems and sold his boat, having never installed this prop. This lengthy explanation put me in suspicion mode and so when I installed it I sat a large wooden block beside the prop so the blades would touch it when I spun the prop. I found that when I adjusted the block till the blade would just barely touch the block. the other two would not hit by a margin of about 2 mm. I thought, "Ah Ha, that's why he sold it so cheap". With that thought in my head, I removed that prop and put my old prop back on and did the same test with the block of wood to see how concentric it was. Low and behold it was about the same. I have ran that prop quite a bit and found nothing wrong with the way it ran other than the low WOT RPMs. I would be curious to hear what others have found concerning this and possible someone in the prop maintenance profession may have some info about how concentric outboard props need to be. Both of these props are Yamaha Saltwater series with the 61A hub. Any input on this is welcome. I have not had the boat out yet with this prop.

 

[seasick]

Although 2mm is small run-out, you might want to use a dial indicator on the output shaft. It may be bent. One way to tell without a dial indicator is to mark each blade, say 1,2,3 and note which blade has the most spacing from the cav plate. Now make a mark on the end of the prop shaft, opposite blade number 1. Remove the prop and reinstall with blade number 2 lined up with the mark on the shaft. Now rotate and see which blades have the most run-out. If it is different blades, the shaft is bent

 

[wspitler]

You assume it is the prop, but your output shaft could also be a contributor. A dial indicator is the best way to check the shaft.

 

[Fishtales]

agree on the shaft... you could take to a prop shop and ask them to do a check.

 

[Halfhitch]

Although 2mm is small run-out, you might want to use a dial indicator on the output shaft. It may be bent. One way to tell without a dial indicator is to mark each blade, say 1,2,3 and note which blade has the most spacing from the cav plate. Now make a mark on the end of the prop shaft, opposite blade number 1. Remove the prop and reinstall with blade number 2 lined up with the mark on the shaft. Now rotate and see which blades have the most run-out. If it is different blades, the shaft is bent

Thanks seasick, I think I can borrow a dial indicator. I have never touched bottom since I've had this motor but that doesn't mean it's not bent. I was not around when the guys were handling it with the forklift during the rigging process. I came to distrust that shop after I saw more of how they worked.

 

[seasick]

Measuring just behind the splines ( between splines and the housing) ideal
should be about .002 inches or less but. Anything under 3-5 thousandths is probably OK.

 

[Halfhitch]

I checked out the prop shaft today and it is true, so I called Burris Propeller in Cape Coral Florida. They are in the family of prop shops that use the Rundquist Tool system and are very well thought of down here. The fellow I talked to said that for recreational/sport boat props with a rubber hubs, they consider the blade thickness at tip to be the amount the blades can vary in radius from one to the other. Mine is probably about 1/2 that so, no worries for me. He said when they are dealing with solid cast racing props, it's a whole 'nother thing. Just posting this in case someone else starts nitpicking their setup in the future.

This is the website of Rundquist Propeller….

http://www.rundquist.com/

 

[seasick]

Good info..Thanks