7.4 MPI with Bravo 3.....have some maintenance questions.

[IQRaceworks]

I recently picked up a 99' bow rider with a 7.4 MPI and Bravo 3 drive. All my experience with Mercruisers has always been on older carbed motors with Alpha 1 drives.

I've wanting to go through and do the standard maintenance things before I get the boat out for a long weekend on the lake. I'm going to change the drive oil, water pump impeller, and fuel filter/water separator.

From what I have read...there is no impeller in the lower unit, there is actually a pump on the motor where the impeller is located. Is that right?

And instead of a standard screw on fuel/water separator.....this MPI should have a cartridge filter located down in a canister next to the electric fuel pump mounted on the motor? Right?

Just trying to learn all I can before I dive into this.

Thanks!!

 

[HT32BSX115]

Re: 7.4 MPI with Bravo 3.....have some maintenance questions.

Howdy,

Congrats on your new acquisition!

From what I have read...there is no impeller in the lower unit, there is actually a pump on the motor where the impeller is located. Is that right?

Yes. There's a belt driven raw water pump on the front/right side of the engine. I would also suggest that you also remove the engine oil cooler and clear it of any debris since previous impeller failures might have deposited fragments there.


Mercury recommends using Mercury HP drive oil. Most of us here either use that or another synthetic gear oil such as Mobil-1 75W90 syn, Am$oil marine gear lube etc..... Make sure you fill it like the service manual suggests.


use some sort of lubricant to get the impeller in the housing......just about anything works. I used vegetable oil.....be sure to bend the vanes in the correct direction. (although some report that it doesn't matter and they'll bend the right way on first start-up...I haven't tried it)

DO NOT tighten the bolts too tight on the raw water pump or you may have the same problem I had......

Now I have a Hardin Marine stainless steel impeller housing installed!



Regards,


Rick

 

[IQRaceworks]

Re: 7.4 MPI with Bravo 3.....have some maintenance questions.

Thanks for the info Rick. I found the fuel filter/separator....but it's not the newer cartridge type, it's the older screw on filter type.

Also, changing the impeller on the raw water pump looks like it's going to be a real pain in the butt. Just getting to it is going to be a nightmare. It looks like I'm going to have to pull the fuel filter assembly off and out of the way just to get to the pump....and then when I get to it, there isn't much room to work on it at all. Is that pretty normal as far as how tight the pumps are usually wedged in there??

 

[MarkSee]

Re: 7.4 MPI with Bravo 3.....have some maintenance questions.

Indeed those can be a pain.

I have the same package as you, maybe 1 year newer, so as you've probably realized getting it done in an hour may be a bit optimistic.

What I have to do is loosen and pull the entire bracket assembly from the engine block forward which then gives enough room to get to the hoses to remove them. Note the position of each hose on the pump housing as it's easy to mix them up. Use something to mark each.
Oh and to get that engine mounted bracket out the big, bottom hose on the water circulating pump needs to get moved out of the way.

Now the entire assembly is off the boat and ready to take the water pump housing off but first, make a mark across 1 or 2 spots on the pump housing and the pulley so it's easier to orientate for reassembly. And the bolts you're removing, they all won't be the same length; take note where they came out from.

Also take note (or picture) before removing the existing impeller the direction the vanes are going.

Since you don't have a history on the last time the housing or plate was replaced, I would buy the entire kit that includes the housing with o-ring already installed. That will also come with new bolts.

Speaking of bolts, the torque spec on the bolts when installing the housing back on the pulley is in "inch" pounds. Accidentally use a foot pound setting and you'll likely break off part of the base and that's a few hundred dollar mistake.

Then putting the entire assembly back on. I pull the hoses forward to attach them to the housing/pulley assembly; then push that back a bit. Get the bracket loosely attached to the engine block then pull the housing/pulley assembly forward to attach it to the bracket. Work and wiggle your way through getting the pulley tightened back to the bracket and bracket to the block. Re-attach water circulating pump hose.

Maybe not all installations need to do this but mine does as I just copied what the mobile mechanic needed to do when I was using him for maintenance while learning.

This should be the service manual for your engine if you don't already have it:
Boatinfo - Mercruiser Service Manual nr. 23 - 1998-2001 - Engines GM V8 454 & 502 CID (Gen VI and L-29)

Mark

 

[HT32BSX115]

Re: 7.4 MPI with Bravo 3.....have some maintenance questions.

Thanks for the info Rick. I found the fuel filter/separator....but it's not the newer cartridge type, it's the older screw on filter type.

Also, changing the impeller on the raw water pump looks like it's going to be a real pain in the butt. Just getting to it is going to be a nightmare. It looks like I'm going to have to pull the fuel filter assembly off and out of the way just to get to the pump....and then when I get to it, there isn't much room to work on it at all. Is that pretty normal as far as how tight the pumps are usually wedged in there??

Unfortunately, yes. Boat builders don't usually give you a LOT of room for routine maintenance. I can change mine without "pulling the engine" or removing any other components. I'm just lucky I guess.

 

[IQRaceworks]

Re: 7.4 MPI with Bravo 3.....have some maintenance questions.

Thanks again for all of the info. Mark, I would have never thought to take the entire pump off and out in order to work on it. I guess that's a much easier way to do it than to try to disassemble the pump while it's still hooked on the motor...way down low where it's hard to get too. I'm going to buy the kit today (hopefully my boat shop has one), and start working on it tonight!

Thanks again!

 

[MarkSee]

Re: 7.4 MPI with Bravo 3.....have some maintenance questions.

....yea, and for a taller and not very nimble guy like me, finding a way to work on things easier is almost a necessity.

One other thing I decided to use when attaching the pulley back to the bracket while in the boat, as dropping/losing lockwashers that go on the studs would take place as that is a reach-down-feel-wiggle activity, I ended up buying some stainless steel nylock nuts instead and not worry about the lock washer.....though I did buy a couple extra nylocks also as I knew dropping and losing at least one is the norm for me....

Mark