undercover
Member
I never change my impellers until they fail because it's somewhat of a pain. I changed one last season and ran OK but didn't prime right this season, and I burned it up. I pulled the pump housing (this is the bronze pump), and it had light scoring wear in it. The merc pumps are $$$, about $700 if you have the air drain valves, etc.
So, I found a different solution - retrofit the more common crank-driven Johnson high volume pump used by Volvo, Indmar, etc. Those pumps are about $150, and changing the impeller is a snap. About 25 hours on the new pumps, and so far so good!
Here's what you need (quantities listed for 1 engine):
1) Johnson Pump F6B-9 (~$150)
2) Mounting Bracket - I used SKIDIM.com part # 49-5200 ($37), but Marine Power 308711 ($26) will work, too, just not as adjustable
3) 1 1/4 to 1 1/2 billet hose barb adapter (ebay ~ $11)
4) Qty 3 - 3/8" ID to 1/2" OD bushings, 3/8" long (ebay $6)
5) 3/8" billet small-block chevy water pump spacer (ebay $15)
6) Qty 3 - 3/8"- 24 fine pitch bolts 1 1/2 inches long (ebay $8) - these need to be small-headed like allen or CV axle bolts. You won't be able to get a socket on the head of regular bolts.
7) 1.25" W x 3/8" thick aluminum flat stock ~6 inches long ($6 onlinemetals.com), this is for spacers; you could use a stack of 3/8" washers if you want instead
8) about 3ft of 1 1/4" marine water intake hose (~$21)
9) Gates K060763 serpentine belt (Amazon $16)
10) optional Mercruiser 862778 alternator support bracket ($21) - I haven't done this yet, but it should replace the bracket with the idler pulley that's no longer used (seen without a belt on it in the photos below)
Installation is straightforward with a couple of things to pay attention to:
- I put a 45 degree 'twist' in the mounting bracket so the pump can be clocked differently (hoses to starboard and down) than standard mounting (hoses to port)
- You MUST use the bushings (item #4 above) in the pump flange bolt holes. These will perfectly center the pump on the crankshaft, otherwise it will wobble. Not sure why Johnson put 1/2" holes in the flange.
- The pulley spacer is to push the pump out a little bit. If you don't use a spacer the hoses will be really close to the serp crank pulley.
- You need to take up the space that the bracket mounts to that was vacated by the original Merc pump and provide for correct alignment of the alternator support bracket. I used the aluminum flat stock, but you could stack washers.
- The merc pump as a 1 1/4" inlet and a 1 1/2" outlet. The Johnson pump is 1 1/4" for both. That's what the hose and adapter barbs are for.
- The serp belt routing changes slightly (see pic), and it's a much shorter (and cheaper!) belt.
So, I found a different solution - retrofit the more common crank-driven Johnson high volume pump used by Volvo, Indmar, etc. Those pumps are about $150, and changing the impeller is a snap. About 25 hours on the new pumps, and so far so good!
Here's what you need (quantities listed for 1 engine):
1) Johnson Pump F6B-9 (~$150)
2) Mounting Bracket - I used SKIDIM.com part # 49-5200 ($37), but Marine Power 308711 ($26) will work, too, just not as adjustable
3) 1 1/4 to 1 1/2 billet hose barb adapter (ebay ~ $11)
4) Qty 3 - 3/8" ID to 1/2" OD bushings, 3/8" long (ebay $6)
5) 3/8" billet small-block chevy water pump spacer (ebay $15)
6) Qty 3 - 3/8"- 24 fine pitch bolts 1 1/2 inches long (ebay $8) - these need to be small-headed like allen or CV axle bolts. You won't be able to get a socket on the head of regular bolts.
7) 1.25" W x 3/8" thick aluminum flat stock ~6 inches long ($6 onlinemetals.com), this is for spacers; you could use a stack of 3/8" washers if you want instead
8) about 3ft of 1 1/4" marine water intake hose (~$21)
9) Gates K060763 serpentine belt (Amazon $16)
10) optional Mercruiser 862778 alternator support bracket ($21) - I haven't done this yet, but it should replace the bracket with the idler pulley that's no longer used (seen without a belt on it in the photos below)
Installation is straightforward with a couple of things to pay attention to:
- I put a 45 degree 'twist' in the mounting bracket so the pump can be clocked differently (hoses to starboard and down) than standard mounting (hoses to port)
- You MUST use the bushings (item #4 above) in the pump flange bolt holes. These will perfectly center the pump on the crankshaft, otherwise it will wobble. Not sure why Johnson put 1/2" holes in the flange.
- The pulley spacer is to push the pump out a little bit. If you don't use a spacer the hoses will be really close to the serp crank pulley.
- You need to take up the space that the bracket mounts to that was vacated by the original Merc pump and provide for correct alignment of the alternator support bracket. I used the aluminum flat stock, but you could stack washers.
- The merc pump as a 1 1/4" inlet and a 1 1/2" outlet. The Johnson pump is 1 1/4" for both. That's what the hose and adapter barbs are for.
- The serp belt routing changes slightly (see pic), and it's a much shorter (and cheaper!) belt.
