Monday, 15 August 2011

Jet Unit - Part 3

A free weekend gave me time to assemble and fit the jet unit with help from a friend. I started by assembling the thrust bearing with a new bearing and new seals (part numbers in earlier post). I then fitted this to the new Duplex Steel shaft having packed the bearing with grease.




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Packing thrust bearing with grease before fitting collar and grub screw.
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Here is the collar in place. The collar squashes down into the thrust bearing and provides a watertight seal with the inner seal, but more importantly, stops the shaft being pulled backwards. I drilled a tiny hole in the shaft to locate the collar in position. Tungsten drill bit was no use on the Duplex Steel shaft, ended up using a die grinder. That stuff is tough as hell! No more bent shafts though!

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I installed the new marginally lubricated bearing and rear seal to the rear pump section (part numbers in earlier post). I also at this stage fitted the new rear wear ring. The wear ring has been machined from ABS plastic and gives a 0.2mm clearance between the impeller tip and the wear ring. On the maiden run of the boat, the clearance was 2mm, way too big, but couldnt do much about it because of the bent shaft. I'm expecting a big improvement in performance and less vibration with the new shaft and tighter tip clearance. The wear ring sits proud of the rear section mounting face to locate in a recess machined in the front section (a modification of mine based on another unit to help align the front and rear sections).
 
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I made up a rubber gasket to fit between the two sections of the pump to prevent any gaps. A good use for an old car tyre inner tube! I siliconed this to the mounting face.
 
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All the jet pump components prior to assembly. Gave the impellers a polish up too, nice and shiny!
 
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Assembly of the complete unit with the shaft and front impeller in place. You can see the bolts in the shaft to locate the rear impeller. This was previously located with a stainless roll pin.

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Fitting the rear impeller. The stainless collar fits over the end of the shaft and sits in the rear marginally lubricated bearing which is packed with grease. This supports the rear of the shaft.
 
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Fully assembled unit. Went together a treat and the alignment recess idea made things a whole lot easier. Wasnt cheap to get to this stage but its better than new now and should last many more years.

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Test run in a few weeks. More updates and videos soon.

1 comment:

  1. Thank you for posting this. Great information!

    ReplyDelete