7.4L Impeller replacement attempt

[Keeb Moving]

I purchased a neglected 92 Wellcraft with twin 7.4K Inboards and closed cooling system. Port engine overheated, so, I bought impeller kits and started the replacement project. The raw water pump is part of the fuel pump assembly. The port engine’s assembly slid right on, then I spent 3 hours trying to get the bolts installed, so, I gave up. The starboard engine impeller will not slide right on. I can force it
On the shaft about an eighth of an inch and can barely pull it back off.
Any suggestions for completing this task?

 

[Scott Danforth]

pull the whole pump assembly and put it on your work bench. that way you can service the fuel pump side of things too.

 

[tpenfield]

I have those combo water/fuel pumps. I am not sure what "slide right on" means.

I have found that the pump body has to be pushed & twisted a bit to get the mounting holes to line up with the bracket. That is because the impeller MUST sit off center within the housing (as that is how the impeller works) . . . . The impeller, being symmetrical makes the pump body sit centered on the impeller and it takes a bit of muscle to make it off-center.

If you get one bolt installed, the next bolt should be as diagonally accross from the first bolt as possible. Eat a good breakfast before you install the pumps, as you will need your strength.

 

[Keeb Moving]

pull the whole pump assembly and put it on your work bench. that way you can service the fuel pump side of things too.

I almost remove the whole assembly but, was concerned about fuel spillage from the lines. Just close the valves and catch what runs out of the lines? What service should I perform on fuel pumps? Apologies, I don’t have a service manual for these
Engines, yet. Source for service manuals?
Thanks!

 

[Keeb Moving]

I have those combo water/fuel pumps. I am not sure what "slide right on" means.

I have found that the pump body has to be pushed & twisted a bit to get the mounting holes to line up with the bracket. That is because the impeller MUST sit off center within the housing (as that is how the impeller works) . . . . The impeller, being symmetrical makes the pump body sit centered on the impeller and it takes a bit of muscle to make it off-center.

If you get one bolt installed, the next bolt should be as diagonally accross from the first bolt as possible. Eat a good breakfast before you install the pumps, as you will need your strength.

I meant that the impeller body slid easily on the the shaft. I agree with you on needing strength for this.

 

[San_Diego_SeaRay]

I almost remove the whole assembly but, was concerned about fuel spillage from the lines. Just close the valves and catch what runs out of the lines? What service should I perform on fuel pumps? Apologies, I don’t have a service manual for these
Engines, yet. Source for service manuals?
Thanks!

Here's a good video illustrating this job for just the impeller:

 

[Keeb Moving]

Here's a good video illustrating this job for just the impeller:

Great video. I wish my engine was on a stand like that!
I am probably going to remove the raw water / fuel pump assembly from the motors for this replacement. I’ve ran out of options and patience to do it while attached to the engines.

 

[Scott Danforth]

publications.brunswick.com

 

[Keeb Moving]

Thanks for the great advice!
I pulled these assemblies and installed the new impeller kits. One of my housings was nearly empty of oil, the bearings feel rough and the fuel pump arm is worn. Also, it appears the shaft is bent as the pulley wobbles...
Should I pay the premium for the mercruiser replacement assembly, instead of one of the cheaper brands?
I’m not sure I have the tools to rebuild one of these...

 

[tpenfield]

You could try the off-brand items . . . Hard to say if there will be a quality difference . . . it might actually be the same part in different packaging.

The Merc branded pump is about $780 and the aftermarket branded pump on Amazon is about $400 for the set - sea water & fuel pump.

 

[Keeb Moving]

Where might I find these engines serial numbers? They’re not on the breather covers.

 

[tpenfield]

Where might I find these engines serial numbers? They’re not on the breather covers.

Look for a tag riveted near the flywheel housing, just above the starter.

 

[San_Diego_SeaRay]

Thanks for the great advice!
I pulled these assemblies and installed the new impeller kits. One of my housings was nearly empty of oil, the bearings feel rough and the fuel pump arm is worn. Also, it appears the shaft is bent as the pulley wobbles...
Should I pay the premium for the mercruiser replacement assembly, instead of one of the cheaper brands?
I’m not sure I have the tools to rebuild one of these...

I used this video as a guide to rebuild my 1993 Bravo 3 sea water pump a couple of years ago. I only replaced the bearings and seals, not the shaft. Still works perfect today. $40 instead of ~$600+:

 

[Grub54891]

When doing the impellers, I cut the heads off of a couple of longer bolts, put them across from each other and install housing. Then the other bolts lune up much easier. Then remove the cut off bolts and put the real ones in.

 

[Keeb Moving]

You could try the off-brand items . . . Hard to say if there will be a quality difference . . . it might actually be the same part in different packaging.

The Merc branded pump is about $780 and the aftermarket branded pump on Amazon is about $400 for the set - sea water & fuel pump.

I just received the Amazon pump and it looks nice. However, I am unable to turn the pulley. There is no Oil and the impeller assembly is already bolted on. Also, there is a loose washer on the water pump side of the shaft. Is this normal?

 

[Grub54891]

There won't be oil in the unit, very few things are shipped with oil. You put it in. Loose washer? Tighten the bolt? Or is it on a mounting bolt? A pic would help. They are hard to turn as you have to move the impeller, and fuel pump at the same time. That belt does a lot of work. I personally don't like that setup.

 

[Keeb Moving]

There won't be oil in the unit, very few things are shipped with oil. You put it in. Loose washer? Tighten the bolt? Or is it on a mounting bolt? A pic would help. They are hard to turn as you have to move the impeller, and fuel pump at the same time. That belt does a lot of work. I personally don't like that setup.

Fuel pump is not attached yet. I only meant, is the lack of oil enough to keep it from turning. The washer is on the shaft where the cam is. Not under a nut. I can try a pic tomorrow, but, I can turn my current assemblies, even the one that is worn out, but the new Amazon one seems locked up.

 

[Keeb Moving]

My Impellers are working however, my port side temperature gauge is not working. It is a new Gauge. I replace the sensor on thermostat housing and temp gauge never went above 100. I replace the thermostat because it seemed like it was stuck open. I still have a slight amount of steam from the port engine my temperature gauge is now pegged out on the highest temperature on the gauge as soon as I turn ignition on. I’m not sure why before the before the thermostat install it would never get above 100° any suggestions?

 

[Grub54891]

Do you have a dual helm? If you do you have to get the right temp sensor for it, same as if you have a single helm. The ohm ratings are different for each.

 

[Keeb Moving]

No, just a single helm.