Repowering 1998 Maxum 2700 SCR -- Mercrusier 7.4

[SDSeville]

Hi All,
Some may remember a thread I had back in October when I had a slow turning 7.4 that would not start. I was away from the boat for about three weeks and when I returned, it was completely frozen. The local marina inspected and diagnosed as hyrolock. Time for new motor or rebuild.

Since I did not want to just put this on a credit card, it took me a several months to save up the cash to get started on this. She will go from the slip to dry-dock in a couple weeks. I am leaning toward a rebuild, but will my block still be rebuildable with salt water sitting in it for 5 months?

 

[HT32BSX115]

I am leaning toward a rebuild, but will my block still be rebuildable with salt water sitting in it for 5 months?

Howdy,

Possibly. Depends on how bad the cyls with salt water are A good machine shop might be able to sleeve a really bad cyl.

A good way to fix it though might be to just slide over to your favorite wrecking yard and find a similar year Chev/GMC pickup with a 7.4L engine and buy it. Then swap the marine stuff over to the truck engine. (this might be the cheapest)

Another way, if you want to duplicate your engine would be to get that same truck engine rebuilt. In either case, plan on getting new manifolds and risers.

If it were me, I would also install closed cooling.

Regards,

Rick

 

[alldodge]

but will my block still be rebuildable with salt water sitting in it for 5 months?

As I remember this was raw water cooled (salt water) and salt water sat for 5 months. Also while the motor was turning over slow, it may have also had salt water sucked up by the oil pump and circulated, so I would say probably not.

You can still take it apart and have it measured and checked out. No issue with pistons and cylinder walls because of reboring

 

[Scott Danforth]

core blocks are between $150 and $400 (whole motor). check car-part.com for your local wrecking yard for a 1996 or newer core.

 

[SDSeville]

How about something like this from remanufactured.com? Pretty hefty core charge, but only $132 to send mine back. Looks like for a little more money, I can add some horepower.

http://remanufactured.com/Inboard_Marine_Engines.htm

CHE	7.4	454	V8	GEN6	Marine	96-06	Big block Chevy 310-350 HP 1 piece rear seal Gen 6 small port efficiency cylinder heads 4 bollt mains Reverse rotation add $600		$2,290	$1,050	$132.50*
CHE	7.4	454	V8	GEN6	Marine	96-06	Big block Chevy 365-380HP 1 piece rear seal Gen. 6 small port efficiency cylinder heads, Four bolt mains upgrade cam kit, Reverse rotation add $300 Roller rockers & hardened pushrods add $350~ Steel crankshaft add $500 Reverse rotation add $600		$2,580	$1,050	$132.50*
CHE	7.4	454	V8	GEN6	Marine	96-06	Big block Chevy 385-400 HP 1 piece rear seal Gen 6 rectangular port cylinder heads, 4-bolt mains, roller cam kit. Options: Roller rockers & hardened pushrods additional $350~. Steel crankshaft add $500. Reverse rotation add $600. Replaces Mercury MAG MPI.		$2,890	$1,550	$132.50*
CHE	7.4	454	V8	GEN6	Marine	96-06	Big block Chevy 425 hp 1 piece rear seal Gen 6 rectangular port cylinder heads, upgrade cam kit, Reverse rotation add $600. Roller rockers & hardened pushrods add $350~ Steel crankshaft add $500		$2,890	$1,550	$132.50*
CHE	7.4	454	V8	GEN6	Marine	96-06	Big block Chevy 450hp 1 piece rear seal Gen 6 rectangular port cylinder heads, upgrade cam kit, Steel crankshaft. Roller rockers & hardened pushrods add $350~ Reverse rotation add $600		$3,290	$1,900	$132.50*

 

[alldodge]

Read thru a small bit of remanufactured engines dot com. Says must return a motor of same which was bought or there can be a difference price. If your motor is bad, you can scrounge up another so long as it is rebuildable. They want to be able to rebuild what you give them, which is understandable. There is a 30% restocking fee no matter if it is there fault or not. If the plastic bag is torn there is a 50% restock fee because motor has to be torn down and inspected. Does have 3 year warranty but several caveats

Comment: There willing to build a 450 hp motor and ask if you want hardened push rods and roller rockers

 

[Lou C]

I can't imagine taking apart an engine with salt water in it for 5 months, if it will even come apart! Mine had salt water in it for about a week or so, and after pickling it, it did come apart fine but it was only 1 cyl really that had water, which I blew out and sprayed everything with fogging oil. The engine always turned over easily with no locking up so the fogging oil really works. I was able to get all the head bolts out, surprisingly enough using an electric impact gun. Did not break any fasteners. This engine had been run in salt water at least 15 seasons before the head gaskets blew due to an overheat. Here most mechanics would not even consider doing that. New or re-man engine time, I don't think they'd even try to use that as a core.

If you continue to run in salt water, be sure to add closed cooling if you install a re-man engine with no internal rust.

 

[SDSeville]

If I got a used truck engine (or remanufactured one), I would have to change the head gaskets, right? ...in addition to swapping all of the other marine stuff over.

 

[alldodge]

IMO, If your in fresh water I wouldn't worry about a marine head gasket, you do want to have brass or stainless steel core (freeze) plugs. . If you get a reman, just get a marine one.

 

[SDSeville]

I am in saltwater, but will be changing to closed cooling.

 

[alldodge]

Reman, closed cooling no need to bother with marine head gasket or freeze plug

 

[HT32BSX115]

Reman, closed cooling no need to bother with marine head gasket or freeze plug

True statement......

 

[SDSeville]

It looks like I can save between $1k (engine shop) and $2500 (Marina) if I strip the engine to a long block and install everything (incl new risers and manifolds) back on the remanufactured engine. How hard is that and would it be a bad idea to attempt that on my own?

 

[alldodge]

Its not hard but will need a torque wrench (auto store rental) and installing the intake would be the touchest part. Just need to make sure its sealed correctly or can have a vacuum leak. Rest is all heavy but easy enough

 

[Scott Danforth]

the L29 cylinder heads alone are 82# each. if your motor is the stock 310hp or 330 hp its the oval port "vortec" L29 heads. base motor makes 380hp at the crank and with a simple cam change to a comp cam xm-284-hr, makes 428hp with the L28 oval port heads.

the rectangular port heads would require a different intake. if you are not running the upper RPM band, the rectangular ports do not do anything except hinder low RPM torque. in fact the merlin 269 oval port heads out-flow the GM 088 rectangular port heads thru-out the RPM range up to 6800 RPM

stock Gen VI (96-2000) 7.4 liter is known as the L29 motor. it has priority-main oiling system, oval port heads, 4-bolt mains, cast crank, forged 3/8 bolt rods and Hyper-eutectic pistons. the rotating assembly will limit the amount of power you can pull from the motor.

I personally would build a motor, and since your starting with a big-block and not completely changing everything, your limited to just the motor rebuild and maybe exhaust manifolds. (potential original cause of water in motor).

check your local machine shop for pricing. many times they are less expensive than buying a crate motor. compared to above, with a bit of searching you can build a really nice motor. below are your normal pricing. you can shave about 15% off that if you wait for sales, etc.

core motor $400 (assuming yours is damaged to the point of non-use)
piston/rings $450
forged h-beam rods $470
Coated bearings $120
Machine shop work $800
oil pump and pickup $100
Gaskets $200
Timing kit $120
Cam $350
lifters $229
new valve springs $130
new damper $42

if you need a new crank $400

to build a 496 stroker (includes crank) is $450 (new crank and $50 for clearancing the block

i would also install a heat exchanger.

 

[SDSeville]

the L29 cylinder heads alone are 82# each. if your motor is the stock 310hp or 330 hp its the oval port "vortec" L29 heads. base motor makes 380hp at the crank and with a simple cam change to a comp cam xm-284-hr, makes 428hp with the L28 oval port heads./QUOTE]

Wow. I have the 310hp. Are you saying I could boost that to 428hp with just a $350 cam?

 

[SDSeville]

Spoke with the engine builder and sticking with stock for this build. I don't want to do anything that would affect reliability.