Bloodless Impeller Changing?
By Tom Neale, 3/10/2005
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Where do they find those guys with the clean fingernails for the pictures in the engine tech manuals? And where is all the blood? I’ve never seen any of these people with clean hands wearing clean Dickies around any boats I know. One of my favorite chapters in these manuals is the one with a guy gracefully removing the impeller to a raw water pump while the engine is sitting on a bench. The pictures usually include a special tool to help. If they showed me, working on my Perkins in my engine room, the photos would be X rated because of the mangled human remains. The manual always says something like, “remove the old impeller and put in a new one,” Sure. That’s like saying, “Just have a baby today.”
Even staging the job is carnage. First I’ve got to sprain my wrist when I reach way down into the bilge to turn off the through hull valve. Then I’ve got to shred my hands on all the hose clamps holding on all those hoses that must be removed to be able to even see the pump. Then I’ve got to get soaked as the water gushes out all over the place, no matter what I’ve done to contain it. Then I’ve got to lie down on my side beside the engine on a bountiful assortment of nuts and bolts and pipes and tubes and various other lethal objects. Lying down on my side means that I only have one arm and hand free. Obviously they planned it this way, because there’s hardly room to get more than a few fingers of one hand into the space where the pump lives anyway. But no problem. There’s a lot you can do with three fingers. You can drop screw drivers, drop screw drivers, and drop screw drivers. This is actually a very good thing, because screw drivers get me in trouble. The real problems begin when I’m able to actually hold the screw driver long enough to start working on those tiny little screws with round heads and straight slots. They hold on the water pump cover plate, and you’ve got to get this off to get to the impeller. Holding screw drivers with only 3 fingers, when I’m prone on my side only a few inches away, means that I usually round out the slots. Occasionally I actually get a few screws loose so that I can drop them in the bilge with all the screw drivers. But this leaves the face plate still on the pump, meaning that it’s time to get out those tiny vice grips for the rounded off screw slots. When I manage to break off the entire head with the vice grips, it’s time to get out a miniature drill. The only person I’ve seen with a drill that small is my dentist. If I could afford him, I wouldn’t be doing this job myself in the first place.
A Few Hints for Easier Impeller Changing 1. Don’t pry the old impeller out with screwdrivers. These damage the pump lip against which the cover plate is supposed to seal. This can not only result in leaks, but also deformities inside the pump which can wear out the impeller much more quickly than normal. I’ve found that pliers seldom work well and will also sometimes mar the inner pump surface. An impeller pulling tool is worth the cost. 2. Any time you go aground or run your engine in particularly silty water, pull the cover plate and check your impeller blades. Look for cracks in the blades where they join the hub and, of course, for missing blades or parts of blades.
A Few Hints for Easier Impeller Changing
1. Don’t pry the old impeller out with screwdrivers. These damage the pump lip against which the cover plate is supposed to seal. This can not only result in leaks, but also deformities inside the pump which can wear out the impeller much more quickly than normal. I’ve found that pliers seldom work well and will also sometimes mar the inner pump surface. An impeller pulling tool is worth the cost.
2. Any time you go aground or run your engine in particularly silty water, pull the cover plate and check your impeller blades. Look for cracks in the blades where they join the hub and, of course, for missing blades or parts of blades.
For years I refused to buy one of these tools because I figured it would take half a day to just get it into the space, if I could at all. But the pretty pictures in the books continuously beckoned. Finally, in sheer desperation, I decided to investigate scientifically. I spent around 30 minutes lying on my side beside my Perkins (after spending about 30 minutes folding my body into position to fit into the space alongside) holding a miniature tape measure in my 3 fingers, so that I could take measurements. I couldn’t see the numbers on the tape measure because I couldn’t get my face in there and because my bifocals were on the bottom of my glasses instead of on the top even if I could get my face in there. Needless to say, I couldn’t extend the tape with the three fingers without dropping the tape measure in the bilge. I finally came to the conclusion that I didn’t have a clue as to whether that tool would fit into, much less work in that space. But seeing the blood stains from the last job, I also came to the conclusion that I was sure as hell going to try. I went down to Boat Owner’s Warehouse in Ft. Lauderdale and bought one. After wedging back into the war zone and fiddling for 15 more minutes, I actually got the tool into place and IT WORKED. The impeller slid on out like a---well, never mind.
But they don’t make a tool for getting the impeller back in—at least not that I’ve seen. That’ll be the next forty bucks, I’m sure. This is not an easy job either. The books say to grip it firmly and, with a rotating motion in the same direction that the pump shaft turns, slide it in, knuckles be damned. Amazingly, this worked this time. It never has before. I think it had something to do with the fact that the job is much easier when all of your fingers are intact and you haven’t lost a few pints of blood into the bilge.
I asked an “official technician” about all this. His answer was simple. “Oh, you just remove the entire assembly from the engine.” I won’t even begin to describe what you have to do in order to “remove the entire assembly from the engine.” Or what you have to remove from the engine to even get to the “entire assembly” so that you can remove it. This could really get exciting when you have to do this in a hurry, as when your engine just stopped pumping just outside an inlet with a squall line coming. If you’re one of the lucky people who have a raw water pump with an impeller that’s easy to change, count your blessings--and your fingers. But be warned. There’s probably some other mission impossible lurking around that hunk of metal. Like changing out that oil pressure sending unit that you can’t see because it’s behind that pump that’s so easy to work on.
Copyright 2004-2008 Tom Neale