Mercruiser 8.1S Impeller change procedure

Pseudomind

Active Member
Jul 1, 2008
2,122
Jacksonville, FL
Boat Info
2011 Hurricane with Magic Tilt Trailer
Engines
115 HP Yamaha Four Stroke
I di d a search and it listed many threads, and no I did not open everyone. Bu , I did not find what I was looking for.

I am trying to find a link or a procedure with graphics on how to change the impellers.

Any help out here?

Thanks
 
Step one...close the seacocks...


I posted details with pics on changing the impellers on my CATs, but unfortunately, I posted most of the details on changing my impellers on my 380DA with 8.1s on the old SRO board.

It helps to have a helper topside to hand you tools. Once you get yourself wedged in under the motor, the last thing you want to do is keep having to get unwedged to go topside for the 9/16 because you only have the 5/8 open end with you.

Start with the starboard side....it's a tad easier to get to. On the port side, I had to remove batteries ( two I think) to gain sufficient access.

I removed the entire pump and did the impeller change at the bench.

Or....you could just take this advise....and wait till they fail....

...... Mine are only replaced when they fail. I split the raw water system and pulse flush the broken bits out of the heat exchangers.
 
The local SR Mech says to loosen the tubes leading to the exhaust on the port side (at least in a 340, but maybe your boat too) and swing the muffler out of the way. I'm pretty sure I'm saying that right. Bottom line - don't expose a new hole in the bottom of your boat, but move muffler out of way. Otherwise, this is the procedure:

http://clubsearay.com/forum/showthread.php?t=5167&highlight=bracket
 
My advice ... take the pumps off and rebuild the innards on the work bench. You need to check for pump body scouring while at it and trying to change impellers on my 340 in the boat is impossible since the pumps sit just inside the stringers.
 
Replacing the impellers is the only normal maintenance item I pay to have done. 4 hours labor and plus parts.

It certainly could / should have been designed differently.
 
Replacing the impellers is the only normal maintenance item I pay to have done. 4 hours labor and plus parts.

It certainly could / should have been designed differently.


Ain't that the damn truth!! I do everything on my boat that doesn't involve lifting out of the water. When I went to replace the impellers, I changed my mind after doing the starboard side. Not having to touch the port is well worth stroking the check for. Next year, I'll pay again, might even pay to have both done.
 
Basic procedure and pretty easy if you have room for you to fit. On my 410 the port is a little tight but not bad.

Close sea water off
Remove belt
Remove the twin pully assembly - there are two bolts and both are different sizes. Deep sockets.
Unscrew the blue drain plug and drain the water.
Tighten the blue plug back in.
Loosen the two hose clamps to pump
Unplug the sensor.
Wiggle, pull and work the pump free from the hoses. It might take a bit of muscle.
Pump out, take bracket off and unscrew housing.
Open housing. Use needle nose pliers and work the old impeller out.
Check housing inside for heavy scoring. If not bad then continue. If really deep scoring then time for a new pump or look into a stainless backing plate and slightly Shorter impeller kit.
Use a zip tie to fold the new impeller blades in. Use a little soap and push the impeller in. Cut the zip tie and continue turning the pully and push the impeller until it bottoms out.
If you think the blades are in backwards don't worry about it. When the engine starts the vains will correct themselves.
Replace the o ring. If it moves use a little grease to hold it in place when putting the housings back together.
Put all screws in until finger snug. Now alternate in a star rotation tightening each screw evenly. Do this several times until good and snug. Do not force them really tight. The screws are brass and will break or strip. Just nice and snug evenly.
Put some soap on the hoses and the pump and work the pump back on. The hoses don't move back so just wiggle and push the pump until the hoses seat themselves.
Bolt the pully and pump back together.
Now tighten the hose clamps nice and snug.
Plug the sensor back in.
Put the belt back on and tighten so the belt is not tight but has a 1/2" pinch together movement.
Open the sea water valve.
Dry the pump and hoses good with towels so when you start the engine you can look for leaks and not be confused if that's residue water or a leak. Generally you don't have a leak at the hose clamps.

Now enjoy your success and have a beer!

For me on my first engine it took 90 min since I went slow. The second engine it took 45 min. The next time it should only take an hour to do both.

Ps. If the pump housing is really scored buy a new pump with a pull. But rebuild the old worn pump. It' good to have a working spare. The spare comes in handy if the seal ring fails on the working water pump. You'll know when that goes bad. The water dripping from the seal hits the pully and belt and sprays all over the back of the engine. And engine hatch. If in salt water that's a mess! Swap it out to get home.

How this helps.

Mark
 
Are the hoses off the back of the pump supposed to be double clamped ar just single clamped?
From factory they are single clamped. Not sure there is enough room "pipe" to secure two clamps. The way the hoses and pump are positioned I can't see how they would move or blow off. Leak yes but not blow off.
 
From factory they are single clamped. Not sure there is enough room "pipe" to secure two clamps. The way the hoses and pump are positioned I can't see how they would move or blow off. Leak yes but not blow off.

I found spare clamps on my hoses so didn't know whether the previous mechanics got lazy and didn't tighten
 

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