Crankshaft Mounted Raw Water Pump 1996 Mercruiser MIE 7.4L Hurth/Borg (Gen IV)

[Chesfisherman1]

First post...thank you for the ability to exchange info.

I currently have twin 7.4L 454 mercruiser with raw water cooling done via a combined raw water pump/fuel pump assembly powered via a V belt pulley.
I have had this boat for 11 years...I do most engine work on my own.
Servicing my port engine is simple.
Servicing my stb engine is a nigh mare...bruises/bleeding/I look like kids at the school yard beat me up after changing an impeller.

This year my fuel pump failed requiring the install of the complete assembly...cost around $700 part...end point would be same maintenance/access issues....blood/etc...NO WAY.

I decided to reconfigure my entire stb raw water and fuel system (take broken one out of service) and replace it with an electrical fuel pump and a crankshaft mounted raw water pump.

I have completed the electric fuel pump install and it operates great (to USCG stds).

My initial hope was to use the old assembly for raw water pump only service...it worked for 1 day but the damage done by the mechanical fuel pump failure was extreme...leaking seals/ball bearing failure/pulley instability....

I need to get the new pump in asap. (installing myself)

For the crankshaft pump I am thinking of the following below....please see attached draft order with parts numbers which includes:
Johnson pump
Lip Seal
Bracket

Will this configuration work for my raw water cooling?
Any input would be very much appreciate.
Best Regards,
Chesfisherman1

 

[alldodge]

It should work, the offshore folks use them a lot. Indmar used them on their 454

Don't forget the longer hard walled 1 1/2 inch suction line

 

[Chesfisherman1]

AllDodge...thank you sir!

I currently have 1 1/4" raw water plumbing...are you saying that I must maintain the the specs of this plumbing when I extend for new mount?

Is the concern on inlet or outlet side of the pump?

How long do you think a job like this will take a guy with an average skill level? 1 hour/1 day?

Is there a chance that removal of crankshaft bolts creates another engine problem? (I seem to specialize in fixing one thing and break another during a procedure)

I would be happy to buy this stuff from iboats if they have it...maybe I missed it on their site...planning to order today for weekend install and fishing!

Chesfisherman1

 

[alldodge]

IMO the hardest part is getting the old stuff off, including the old hose. Now you could use a short piece of new 1 1/2 inch hard wall for the suction side with a brass double barbed fitting a clamps, but I would get new hose.

Keep in mind I have never converted one, only replaced what was their. Your going to need some longer bolts, the ones removed from the crankshaft pulley will be to short to reattached with the pump. There should be some instructions with the pump, but it's pretty simple, just hard to get at. Your new bolts should be the thickness of the pump plate longer then the originals.

Make sure your hoses are positioned to not put stress on the pump. The bracket which attaches to the block is just to keep the pump from turning while the motor is running. Here is a couple examples

 

[Chesfisherman1]

AllDodge...Excellent advice! Thank you for your time and effort. Did not have extended bolts on my list but just added. Strange that mercruiser does not sell a conversion kit. My marina just wanted to install the original part =$700 and did not encourage any mods. Most boats with twin inboards (maybe even IOs) have extreme poor access to the outer sides of the engines from the engine room and even with my engine covers 100% lifted (my boat has 12 ft beam)=poor matenance=not checking gear oil level in mechanical fuel pump=failure. My other fuel pump has the slight oder of gas/water=doing repeat procedure on my port engine soon. I think my cost per engine is around 350 in parts and 8 hours of labor...Port please don't fail until after the big fish have left the bay.
Best,
Chesfisherman1

 

[alldodge]

I would if I could, I'm another which have to hand upside down to change. But only have about 2 inches in front of the pulley

 

[Bt Doctur]

Most engines use 3/8ths fine thread in the balancer and this may be a bit small for the pump flange.I just installed this type in a VP 5.0 and found the imbalance in the pump when rotated. Machined up collars for the od of the stud/bolt and the id of the pump flange.

 

[Chesfisherman1]

BT Doctur/AllDodge,

Pump is installed and it works great...low no wobble...my old combo water pump/fuel pump nightmare is offically-OUT OF SERVICE-on my stbd engine.
My final pump purchase was different than my order above. See picture below for part number from Johnson Cateloge
The pump I installed is in the picture below....and was a direct fit into my crank pulley. (I had hours of research and plenty of doubt I had the wrong pump)
Given there is no mapping of Mercruiser Engines to a crank mounted pump (on General statements on GM big block) this should be good validation for others.

CONSISTENT BOLT LENGTH IN PULLEY AFTER PUMP INSTALLATION (AllDodge input prior to install...thanks again).
-pulley bolts removed were 3.2 inches in length-fine thread-(per my caliper)
-pump thickness at mounting plate is .4 inches
-Wanted to ensure I maintained the 3.2 inches total length with new bolt arrangement.
-I ended up with 4 inch bolts installed in the following order bolt head-washer-pump mounting plate-3 .2 inch washers screwed directly into the pulley threading.
-I believe the washer helped keep the pump in a "center of rotation" position on the crank pulley where I just did an even torque to each keeping it aligned as best as possible when tighening each of the 3 bolts.

UNCLEAR IF MOUNTING SUPPORT IS REQUIRED
-I purchased a support bracket that did not align well with my engine. Maybe I bought the small block vs big block bracket.
-After reconfiguring my plumbing of 1 1/4" hose I ensured there was no added pressure to the pump by the hose with tie wraps...no wobble/no spin/no problem.

NEED FOR RECONFIGURATION PER PUMP INSTALL IS 5"
-I was going to make this work regardless of the space impact it may have on my engine room.
-I did need to move one of my batteries to an outer position to ensure there was no chance for rubbing/touching/etc..installed spacer around battery to ensure separation and belted the battery down.

NEW PLUMBING:
Raw water intake was a breeze given close location to sea ****. Had 1 1/4" heavy reinforced tubing where I was able to "cut to lenght"
Pump outlet to engine system intake (my intake is at base of the transmission heat exchanger) was a major pain in the rear.
I was going fishing that day and no one had the required hose in stock so I used a 1 1/4" fiberglass reinforced PVC tubing, ran it for about 6-7 feet and ensured it would not contact engine.
Getting hose on the hard to reach heat exchanger fitting was very difficult but go her done.
Temp during outing....never exceeded 160 per my thermostat...
This operation plus the electric fuel pump install completes my grease monkey near term work...now I can enjoy my boat.
Thanks again for your support.



Thanks!

 

[alldodge]

Glad it worked out. :thumb:
Would recommend getting the support bracket, over time that bracket will help the pump last. The vibrations can take it's toll and if something started dragging, then maybe seize you wouldn't want the pump to tear the hose off.

Vibrations over time by them selves can break things.