Saturday, December 23, 2023

Rattle Can Rebuild Part 4

 As I go through the engine I'm looking for things that don't look right and it didn't take me long to find something.  The picture above is the raw water pump drive gear.  Basically, it's a gear that's driven off the crankshaft through a series of gears in the timing case and the slot in the middle is where the water pump impeller shaft inserts into.  The arrows in the picture show where the slot is gouged or worn from the water pump impeller shaft hitting it.  I'm not sure why this happened, but maybe it's normal wear for an engine with 974 hours.  

Fortunately, I have a new drive gear and bearing set, but I wasn't sure how to get at it.  The Westerbeke W27 schematic indicates that it is accessed by removing the timing case (or at least I thought it did).  The timing case is not something I want to get into, because in order to take it off, the govenor spring needs to be disconnected from the high pressure injection pump and it's accessed through a small plate on the side of the engine.  The manual states several CAUTIONS about how fiddly this is and if you drop the spring, you are screwed.  I'm certainly not a diesel mechanic, and warnings like that scare me.

I did a bunch of googling and forum posts asking around about how to get at the drive gear and because each engine does things a bit differently, I got a bunch of opinions that were all over the place.  Finally, I emailed the picture above to Hansen Marine Engineering and asked 1. Is this bad, 2. If so, how do I replace it.  Fortunately, they got back to me within a day and said this is a common problem and it should be replaced, but to do so simply requires removing the bearing housing that the raw water pump bolts to.  Yay, no timing cover removal!

With my newfound knowledge, I got to work and unbolted the bearing housing and within 5 minutes I had the old gear in hand.  To reinstall, I just had to seat the 2 interference fit bearings on either side of the gear.  Of course, you can just drop them on, they have to be pressed on.  I didn't really want to take it to a shop and I didn't want to hammer them on (and risk screwing up the bearings) so I tried a fun trick that I had used before when putting bearings on my tractor mowing deck spindle.

I put the gear in the freezer overnight and the next morning I heated up the oven to 275F and put the bearings in for an hour.  The theory is that the shaft of the drive gear will shrink slightly in the cold and the bearing races will expand with the heat.  Once everything was sufficiently hot and cold, I pulled the gear from the freezer and the bearings from the oven and with a hot mitt slipped them on.  One side slid on with little effort and the other side took a few taps from a plastic mallet on the inner race but it worked and once the temps equalized, the bearing were tightly fitted onto the gear. 

Now that the bearing and gear assembly was all together, reinstallation was just a matter of reinserting the gear and bearing housing assembly into the back of the timing case and bolting it back on with a gasket.  Super simple, but a lot of hand wringing along the way.  I might just become a diesel mechanic yet!

Next up, I assembled the actual raw water pump which consists of a housing (part #048080), the impeller shaft, 2 bearings, and a series of seals and washers to keep everything watertight.  Fortunately, the schematic is very good for this assembly so it wasn't difficult.  I still have to paint the pump housing, but once that's done I can bolt it onto the drive gear housing and call it a day.

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