Nov. 28, 2024
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I like to replace my impellers within a 3 years period in the 4 outboards I run. In my Cummings diesel and Northern Lights diesel genny, I also go 3 years, but in the off season I also remove the impeller from the housing so it can relax and the vanes do not take a "set" and it only takes 10 minutes on the diesels.Personally I do not feel that under 3 years is necessary unless you run in sandy water or have dry-run the motor. Otherwise it's like handing money over to the dealer (I do all my own maintenance).Over 3 years I feel adds risk to the ownership equation. We all know someone that has run for well over that, but the risk factor does go up and since parts are inexpensive, it doesn't hurt replacing.Over the years, I have seen a number of failures of impellers in the first year they were installed. I do not have pics of them all, but share this one of a Merc outboard with a brand new impeller with no more than 5 hours of runtime. The inner collar separated from the rubber and the motor lost cooling and overheated. Since this was a friend of mine on our summer cruise, I know how the boat was run and we diagnosed after the motor overheated. It was not dry run and it was installed correctly. It just failed.I've seen this same concern occur on Evinrude, Yamaha, Tohatsu outboards and Volvo and Westerbeke diesel inboard impellers over the years working on boats.D-
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pabloescobar said:Click to expand...
If you are repitching your Hooker impeller, then you should work with dave at impros to find the correct pitch. He designs the impellers and should be able to help you best.TBM cones in combination with big hub impellers will provide you with a 'poor man's MAG pump.' I used to run that setup with my XS865. They will hook up better than a stock pump, but aresubstitute for a MAG pump. The TBM setup still leaves you with a bighubbed oem pump with long thick cast aluminum vanes. The MAG pump usually has 12 vanes that are much shorter and much thinner stainless steel. Additionally, the center hub is smooth without the joints found all over the TBM.OEM 144mm Yamaha pump vane section was designed in when Yamaha introduced their 'powerhouse' 650 motor in the superjet and WR3. It was never changed or improved when they introduced the 61x 701 motor in or the 62t/61x motor in .In , yamaha redesigned the SJ hull bottom for better hookup by changing the pump intake area and by lengthening the driveshaft and moving the whole pump back by 2". This setback of the whole pump is not be confused with the setback stator vanes within the Mag pump, see below. This improved hookup but still didn't change the original pump design. While it is super impressive that the oem pump designed for an anemic 650 will still work for with a ported 701/760 with a bpipe/etc. It also isn't an optimal setup for performance.MAG pumps have bigger hubs to increase the pressure and the power of the thrust out of and through the pump. They also have more veins which are redesigned and thinner (stainless vs cast aluminum) so they straighten the water flow better. They also will produce thrust even with less than optimal water flow, which is most of the time when you are riding. Another big difference that I notice is how quickly the MAG pump will rehookup when you land. When you ride in choppy water, it is amazing the difference.The setback MAG pump requires a custom setback driveshaft. The pump stator veins are moved back (setback) closer to the reduction nozzle. This leaves room for more water in front of the pump for longer hookup. I have never compared the differences directly to be able to comment on the difference from actual testing.As far as sealing the pump to the shoe, I prefer to align the pump/wear ring and seal it up well. Whenever you remove the pump after that, leave the wear ring sealed and aligned in place, just remove the pump/driveshaft for impeller swaps.
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