Water pump conversion to crank mounted for 496 engine?

Danny Troy

Danny Troy

Member
Oct 8, 2009
861
Candlewood Lake, CT
Boat Info
2003 280 Sundancer
Engines
496MAG w/genset
I called a company that sells the Johnson pumps conversion pumps today and was advised Johnson doesn't make a conversion water pump for the 8.1L engine. The 8.1 has a 4 bolt crank, and the Johnson pumps are for 3 bolt cranks. Any idea on where to get a conversion for this engine? I'm about ready to put in a new impeller, and after the last installation I'm not looking forward to it. For those that don't know about this conversion, it moves the water pump from a tough to reach location, to right up front. Impeller changes take minutes, not hours.
 
You could try Jabsco for the pump. I don't know if they (or anyone), offhand, has a "full conversion kit", though. Meaning, you might have to measure for new hoses and cut them to length.
 
That's the wrong pump - that's the circ pump. You need a 'sea water' or 'raw water' pump. They're going to be in the $500 neighborhood. Check out Jabsco's website.
 
Any idea of their website? I found a UK website, but not a US site. Looks like it's going to be difficult to find a conversion pump for the 8.1L. I understand I'd have to provide the proper size/length hoses. They should be easier to find than the pump.
 
http://www.xylemflowcontrol.com/jabsco/

Then click on 'engine cooling'. I had the correct part number written down somewhere as to which was the correct pump to use, but I can't seem to find it. I seem to recall talking about this in another thread a little while ago and I may have noted the part number there - if you wanted to search for it, that is. But if you look through the info on there site, and a particular pump, it should tell you what engines it fits.

On a side note... you have a big engine in your bilge, but it's only one which means you have pretty decent room to work with (when it comes to working on boats, anyways). Did you try and change the impeller ON the engine? The easier way is to remove the whole thing - bracket and all - and do it back on your workbench. This process works great on a small block - I haven't worked on a 496 recently to say for sure, but assuming you can do the same thing it makes this a pretty easy job. For example, on my engine (350) I could have the entire pump assembly out of the boat in about 10-15 minutes, if I'm taking my time. The whole job - an hour.
 
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I checked that site and couldn't figure out exactly what pump would work. I emailed them and hopefully will get a response soon.

I have already done an impeller replacement on my engine and it wasn't fun. Of all the bad locations to put the water pump, this has to be one of the worst. I couldn't imagine doing it with twins. I did what you said, remove the entire assembly and replace the impeller with the entire pump out. Definitely the way to go. I'm beginning to think there is no conversion for the 496, since I haven't actually found one site where a 496 conversion was done.
 
Danny Troy said:
I have already done an impeller replacement on my engine and it wasn't fun. Of all the bad locations to put the water pump, this has to be one of the worst. I couldn't imagine doing it with twins
Click to expand...

you should try it with twins 'AND' with V drives that cause the engines to be reverse mounted with the pump facing the transom....

cliff
 
Danny, when you get to the page I referenced, it shows you their models. I only looked VERY quickly, so double check on all this, but when you click on the 50410 model it says it works with GM 8.1L engines. Wouldn't that be it?

Another option is to get one from a Volvo dealer as they usually use crank-mounted pumps.
 
Dennis, good find. Thanks. That definitely looks like it would work. The only question is the flow rate. As far as I know the stock water pump puts out, from what I remember, about 24 gal/min. The Jabsco puts out 14gal/min. Quite a difference, although I don't know at what RPM the 24gal/min for the stock unit might be. Also, do you know the difference between the two types. The Lip flow and the Carbon Ceramic type.
50410-140150410 Flange Mount 1 1/4" Pump
Replaces 22400-0201
SealLip type
CamFull Flow


50410-150150410 Flange Mount 1 1/4" Pump
Replaces 22400-0301
SealCarbon/ceramic mechanical type
CamFull Flow
 
Danny Troy said:
Dennis, good find. Thanks. That definitely looks like it would work. The only question is the flow rate. As far as I know the stock water pump puts out, from what I remember, about 24 gal/min. The Jabsco puts out 14gal/min. Quite a difference, although I don't know at what RPM the 24gal/min for the stock unit might be. Also, do you know the difference between the two types. The Lip flow and the Carbon Ceramic type.
Click to expand...

My thought, too. I've never even seen a published flow rate for the Merc-designed -- where did you get that info from? Here's a work-around -- IF, by chance, Volvo is simply using a Jabsco (or whatever company) pump... find out the model and you can buy one that way (without having to go through a Volvo dealer). Maybe a Volvo forum - or possibly even contacting Volvo directly. Maybe contacting Merc directly can provide some more info on flow rates, too.

Lip vs Carbon... No, I do not. At least not without googling and research. But I do not know, myself.

Interesting side note... Merc's new 4.5L V6 now has........ a crank mounted pump! :smt001
 
I was trying to locate the site I saw the Merc flow rate, but lost track of it. I've been doing so much research on this, it's a bit confusing. I have three calls/emails and haven't had one person to get back to me yet. One good thing, when I called a company that sells Johnson pumps, I mistakenly told them I have a 4-bolt crank. They advised me they only have pumps for 3-bolt cranks. I messed up there, as I was looking at the circulation pump pulley, not the crank. Checking today, I see I have a 3-bolt crank.

One thing that concerns me is the water pump mounted sensor on my existing pump. I don't think any crank mounted pump has this feature. I suppose it's a temperature sensor. What will happen if I run with that sensor disconnected???
 
UPDATE: Just spoke to guy at Michigan Motorz. They sell the Johnson crank mount pumps. He said it can't be done on the 496. He recommended going with a serpentine belt driven Volvo pump, and he knows for a fact people are using that setup on the 496. Off to do more research......
 
Check a site called Offshore Only. It's a go fast site and lots of owners have done the swap on many different size engines.
 
I just looked up the flow rate for a mercruiser pump in service manual number 23. GMV8 454cid (7.4L) / 502 cid (8.2L)
At 1000 RPM it is 7.5 gallons per minute minimum
 
I'll check that Offshore site. I think I'll have this figured out in a few days. I have some photos of the Volvo engine, and see how great the design is. Looks to me like it should be an easy conversion, other than the plumbing, using the Volvo pump.

Good to hear the stock Merc flow rate is lower than the replacement pumps. The flow rate of 24 gal. was quoted by someone on a site, who was obviously very wrong.
 
This is a little late, but why do you want to convert the pump? If you have had cooling issues there other culprits than the water pump to consider.

If the pump is up to par, then there is a possibility the raw water flow is being blocked where it goes through the transom assembly. You might consider investigating this before trying to re engineer the motor.


Henry

Sent from my iPad using Tapatalk HD
 
Henry Boyd said:
This is a little late, but why do you want to convert the pump? If you have had cooling issues there other culprits than the water pump to consider.

If the pump is up to par, then there is a possibility the raw water flow is being blocked where it goes through the transom assembly. You might consider investigating this before trying to re engineer the motor.


Henry

Sent from my iPad using Tapatalk HD
Click to expand...

Henry,
i believe the OP stated in his original post that he wants to relocate the pump for easier access when changing impellers....

cliff
 
Yes, if was was 30, or better yet 40 years younger, it would be twice as easy, and still be a PITA to change this impeller! I have no cooling issues, I'm just looking ahead, as I plan on keeping this boat and would like to make the job and lot easier.

BTW, I checked the offshoreolnly site David recommended, and it's a wealth of information. From what I have read, it looks like the Jabsco 50410-1401 should work.
 
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