Re: Raw water pump maintenance
Jim, I'll toss in my two cents here if you don't mind.
I'm not a Merc guy, but I do understand sea water pumps, and most operate very similarly to one another.
First, your style pump does not use a cam, so if you read anything that suggests to replace the cam, pay no attention to this.
Your style pump places the impeller shaft eccentrically within the pump body to create the same action as does a pump with a cam.
Difference being that the eccentrically positioned impeller causes the same three/four vanes to be folded over to create the suction/pressure as does a cam with an impeller shaft that is center positioned.
Here's an impeller pump that uses a cam to fold the vanes over.
The shaft is dead center within the pump.
This is not your Merc pump... examply only, but will be very similar in function!
If you look closely, you'll see that there is no cam and that the impeller is eccentrically positioned off to one side.
In some respects, this style doesn't wear the impeller from cam friction.
All sea water pumps have two thrust surfaces and are where we'll see the grooving.
More so at the side where the intake/pressure ports are, since it's more likely that debris will be brought in at this side.
Ditto the resurfacing of the thrust surface. Most can be saved if the grooves are not too deep.
As an added note, impellers that are used more frequently tend to outlast impellers that undergo winter lay up for long durations.
When an impeller sits at rest within the pump body, these same three/four vanes that are folded over against the cam or eccentric (such as in your case) tend to cause the material to take a "set".
Here is an impeller that is damaged simply by Father Time.
The material has lost it's resiliency, and if you look at the 6:00 O'clock area, you'll see the set.
This "set" is more harmful to an impeller than continued usage is.
Point being: If you lay this engine up for winter, it's more likely that you'll want to change the impeller more frequently, IMO.
I use the crankshaft pumps on my engines. These are very easy to access the impellers by simply removing a cover plate.
I pull the impellers each winter and store them.
This saves them from the "set" that would otherwise occur had I left them installed for the duration.
With your belt driven pump, this is not as easy.
However, if you are removing the pump to inspect the impeller upon re-commissioning, you might want to consider doing this at lay up time, and just leaving the impeller out.
I believe that Merc makes a recommendation for a two year service interval.
I can't bring myself to leave an impeller installed for the winter lay up without at least looking at it come spring time.
Your call on that!
Rick ... aka Ricardo
28' SDN F/B w/ twin Volvo Penta 5.7L DP's