Crank mount pump conversion - any reason NOT to do it

[bobofthenorth]

I see a few other threads here about doing the conversion but at the risk of duplication I'll start another. Any reason not to do this? I've got a 1990 2755 Baylurker with a 350 and Alpha One drive. I hate changing the leg mounted impeller and I don't see any reason to continue doing that. I owned a Malibu Response with a Chev Indmar conversion that had a front mounted impeller. I could (and did) change that impeller in under 5 minutes on the water. I'd like the same convenience on my Baylurker. Anyone here done the conversion and regretted it? Or know somebody that wished they'd left it alone? Or just have an opinion that its a generally bad idea?

Assuming its an OK idea - any links to kits would be appreciated. My boat is outside in a snowbank right now but one of these days I'll push it indoors for winter maintenance.

 

[Scott Danforth]

the alpha drive uses the cooling water to keep the housing cool

 

[bobofthenorth]

This is an Alpha One Gen One. Not being argumentative but the water passes briefly through that housing with no jacket or fins. The cooling effect would be minimal at best.

(edit) I just went and looked at a spare drive and I see that there is a minimal jacket so I stand corrected but I have to wonder how much that little bit of cooling matters. It looks like the water path is up from the pump into a jacket on the port side of the bottom of the upper housing and then directly to the engine.

 

[Scott Danforth]

only reason I mention it is when you change a 4.3/5.0/5.7 with an Alpha to a full system HX and run a separate pump. you swap to a bottom pickup and cut the hose from the drive and keep the leg mounted impeller to keep the drive cool.

 

[bobofthenorth]

Don't you just love it when some ass comes on a forum, asks a question and then argues with the answer he didn't want to hear?

I was thinking if the cooling really amounts to anything I could just loop that hose inside the hull and pump it back overboard. That way if the drive impeller gets changed every 5 or 8 years it will likely still pump all the water that is needed. For engine cooling I'd like to change impellers every year but I 100% know that isn't going to happen with the current configuration.

 

[kenny nunez]

Mercruiser suggested in a service manual to connect the supply from the drive pump to the thru hull fitting using a “Y” connection On the MPI models. I set my Donzi up that way and it worked perfect. If your exhaust exits through the drive then you want to keep the water going through it. You cannot go wrong with a crank driven pump.

 

[Scott Danforth]

volvo only recommends changing every 2 years

 

[kvkon]

Interesting topic. I'm thinking of using the leg pump for the PS, fuel cooler and exhaust manifold supply and a crank driven pump for the HX supply. Is there a kit system supplier for the crank drive pump?

 

[kenny nunez]

Marine Power in Pontchula,La. They have the belt drive or the crank nose style. If you have 6” in front of your crankshaft then the best one is the crank nose style like Volvo has used and are the easiest to service. The belt driven style is more compact but depending on your boat‘s bilge design could make it hard to service.
The advantage of connecting the drive pump to the crank driven one makes it easier to use a flush out, the drive pump will push enough to the crank pump for flushing out .

 

[Scott Danforth]

Interesting topic. I'm thinking of using the leg pump for the PS, fuel cooler and exhaust manifold supply and a crank driven pump for the HX supply. Is there a kit system supplier for the crank drive pump?

Suggest you start your own thread vs hijacking one.

Simply google johnson f6b pump

 

[bobofthenorth]

Interesting topic. I'm thinking of using the leg pump for the PS, fuel cooler and exhaust manifold supply and a crank driven pump for the HX supply. Is there a kit system supplier for the crank drive pump?

So far I haven't found a conversion kit. I'm sure I've seen them in the past but so far nothing. I just looked at the Marine Power site referenced but there's nothing I can see there. Its not rocket surgery - I'm not particularly worried about making something homebrew. I like the idea of teeing in the supply from the outdrive pump somewhere near the raw water pickup. That solves the problem of disposing of the water from the leg. I don't like the idea of trying to suck up water through the leg. If I succeed in finding a conversion kit I'll absolutely post the details.

 

[Scott Danforth]

there is no "kit" there is the front mount pump and you will need the anti-rotation bracket. from there, you need to source hoses.

depending on your motor size, you would run an F5B or F6B. the 5.7 and below can get away with the F5B, however above requires the F6B

Pump Sizes F35 - F95

www.spxflow.com

https://www.spxflow.com/assets/pdf/JPM-Marine-Catalog-2018-US.pdf#page=48

you then buy it here (F6B) https://www.google.com/search?client=firefox-b-1-d&q=johnson+pump+10-24946-01

here are sources for the anti-rotation bracket for a small block

Small Block Crank Mounted Raw Water Pump Bracket | Marine Power 308711

Holds crankshaft mounted raw water pump used on Marine Power GM small block marine engines in a stationary position while the engine is operational.

marinepartssource.com

or here

Barr Marine 495200 Small Block Raw Water Pump Bracket

Barr Marine 495200 Small Block Raw Water Pump Bracket

www.marineengineparts.com

or use the stock volvo bracket or make your own.

the inlet hose should be hard hose or have an internal spring

the discharge hose can be a soft hose or a formed hose. I use the gates catalog. https://assets.gates.com/content/da...gs/gates-molded-coolant-hose-id-guide_web.pdf

 

[tank1949]

I see a few other threads here about doing the conversion but at the risk of duplication I'll start another. Any reason not to do this? I've got a 1990 2755 Baylurker with a 350 and Alpha One drive. I hate changing the leg mounted impeller and I don't see any reason to continue doing that. I owned a Malibu Response with a Chev Indmar conversion that had a front mounted impeller. I could (and did) change that impeller in under 5 minutes on the water. I'd like the same convenience on my Baylurker. Anyone here done the conversion and regretted it? Or know somebody that wished they'd left it alone? Or just have an opinion that its a generally bad idea?

Assuming its an OK idea - any links to kits would be appreciated. My boat is outside in a snowbank right now but one of these days I'll push it indoors for winter maintenance.

Lots of new plumbing required for a little bit of gain, if that.