Question: What’s the best direction to go when replacing the old Mercruiser 3.7L/470 marine engines?

Unfortunately there is no single good option for this when looking at a complete re-power. The 470 was originally developed by Mercury Marine specifically for it’s purpose; to power boats. The inline configuration allowed for easy draining, a single intake/exhaust manifold was cheaper than two, etc. The engine was also a large displacement engine for its size and therefore made a tremendous amount of torque because of the stroke and displacement. On top of this Mercury utilized their die casting expertise to produce a light weight aluminum block and combination with the existing Ford cast iron 460 cylinder head.

To go up in Hp you will have to go with the typical V-Configured  350 engine which will also require a different drive ratio and propeller. With any changeover to the V engine configuration be it V6 or V8 this will also require completely rebuilding the stringer system in your boat. Many customers ask about replacing the 470 engine with the current 3.0L engine since they are also are an inline configuration. The problem with this is that the 3.0L makes approximately 135 Hp & 180 Lb-Ft of torque where the 470 made 190 Hp and approximately 275 Lb-Ft of torque. The 3.0L engine is simply too small and does not make enough torque.

Recommendation

Therefore the prevailing direction for 99% of boat owners in this position is to go with the remanufactured 470 longblock. The remanufactured longblocks are of a very good quality and have a 24 month warranty. This is important versus rebuilding realizing this was not a standard automotive product and therefore most local rebuild shops do not have the experience to produce a comparable, good quality product.

In some cases certain customers really love their existing boat but prefer more horsepower/torque. If this is the case for you it may be worth the time and investment to investigate changing over to the larger displacement “V” configured engine, however in 99% of the instances the only viable option comes down to replacing the longblocks or simply changing boats.

Installation Drawings for reviewing specific dimensional differences (open is separate windows)

470 (1976 Model) Installation Drawing (Select Link)

470 (1978 Model) Installation Drawing (Select Link)

3.0L (Inline 4 Cylinder) Installation Drawing (Select Link)

4.3L (V6) Installation Drawing (Select Link)

5.7L (V8) Installation Drawing (Select Link)

Tech Tips (Select Link)

Remanufactured Longblock Product (Select Link )

BREAK-IN PROCEDURES 

“Break-In” Procedures for 4-cycle MerCruiser Engines

IMPORTANT: The first 20-hours of operation will have a dramatic affect relative to overall engine performance and expected engine life. Proper break-in practices reduce the potential for excessive oil consumption. It also helps to achieve better engine performance levels for a longer period of time.

FIRST 20-HOURS:

1.      Do NOT operate the engine below 1500 rpm for extended periods of time. Shift into gear as soon as possible after starting the engine. Advance the throttle above 1500 rpm if conditions permit safe operation.

2.      Do NOT operate at one continuous speed for extended periods of time. Vary the throttle position every ten to fifteen minutes.

3.      Do NOT exceed ¾ throttle during the first 10 hours of operation. During the next 10 hours you may occasionally operate at full throttle for no more than 5-minutes at a time.

4.      Do NOT operate at full throttle until the engine reaches normal operating temperatures.

5.      Avoid full throttle acceleration from an IDLE speed.

AFTER FIRST 20-HOURS:

To help extend the engine life for the engine, consider the following recommendations.

1.    Install and maintain the correct propeller for the application. Make sure the prop allows the engine to operate at (or near) the top of its specified Wide-Open-Throttle rpm range. Refer to the Owner’s Manual, or consult with your marine dealer to determine the correct prop for the application.

2.    Refrain from extended periods of Wide-Open-Throttle. We recommend cruising at ¾ throttle or below for longer term operation.

3.    Change the oil and filter regularly. Refer to Specifications and Maintenance section of the MerCruiser Owners Guide for recommendations

Left Hand (LH) rotation is considered to be standard while Right hand (RH) is considered an “Opposite” rotation. You should ALWAYS view the the engine rotation while standing behind the engine and looking at the flywheel. 

A LH engine spins CCW (Standard Rotation)

A RH engine spins CW  (Opposite Rotation)

IMPORTANT: It is extremely important to note that engine and propeller rotation are not one and the same. In most cases the propeller rotation will differ from the engine rotation due to the gearing.
A few of the older, “Iron-Body” transmissions with specific ratios would turn either direction.  But, in general, when standing at the back of the boat looking forward, with a single STD Rotation (LH/CCW) engine, most of the transmissions turned CW (opposite of the engine).  This is the same as the sterndrives and these applications require a RH prop (if the driver is on the right-hand side, this compensates for “boat role” due to the driver weight).

For twins, the RH prop is normally the STBD and the LH is the Port, ‘OUT’ (although this probably doesn’t make much difference for inboards but this gives the best steering control for sterndrives).  Typically rotating the props ‘IN’ allows a little more top speed but less overall vessel control.

Stern Drive (Inboard/Outboard, Outdrive)
The engine is mounted inside the boat. The transmission/drive unit is outside, attached to the transom. The engine and drive unit are joined by a torque coupler and universal joint. Angling the drive steers the boat.

Inboard
The engine and transmission/drive unit are inside the boat. A drive shaft is connected at the rear of the transmission and is run out of the hull through a sealing unit. The propeller is connected directly to the drive shaft at the in-water end. A separate rudder steers the boat.

V-Drive
Basically a modified inboard installation. The engine is mounted with the front (pulley end) facing stern (rear). The transmission faces the bow (front) and by the use of a universal joint on the end of the transmission, the drive shaft is directed stern-wards under the engine and through the hull. The propeller/rudder arrangement is the same as in a standard inboard installation.

Jet Drive
The engine is mounted inside the boat and attached to a high speed pump which draws in water through an intake grate, increases its velocity and forces it out through a directionally adjustable nozzle which is mounted outside the boat. Changing the direction of the nozzle steers the boat.

RETURN TO BOAT REPOWER GUIDE MAIN PAGE

Topic: Boat Repowering (Part 1)

Question #1: How do I determine the condition of my Marine Engine so I can better understand how to approach my boat repowering needs?

Response: The quick and easy answer is to perform a compression test, however this is not always the best approach as it only paints a portion of the picture to the overall condition of the engine. With regards to determining the overall condition of the engine whether it applies to purchasing a boat or developing an approach to repowering the boat you already own we would divide the this into two separate categories; condition of the accessories and condition of the base engine itself. With regards to the condition of the accessories much of this is visual however determining the condition of the base engine you will need to perform a few tests.

Part 1 – Visual Inspection of the Engine Accessories
1. Is the engine operated in Salt Water? This may affect the condition of the electrical components that cannot be seen visually. However in general signs of corrosion can be seen on the metallic connectors.
2. Exhaust System – Remove the Exhaust Bellows to inspect the snout of the exhaust elbow/riser. Also check the sealing joints between the manifold and elbow for leakage. Select this LINK to read more about corrosion and view images.
3. Engine Circulating Water Pump – Inspect the underneath side just below where the large J hose conencts on the inlet side of the pump. This is where the weep hole is located that indicates pump seal failure.
4. Starter – Visually inspect the starter for signs of corrosion.
5. Alternator –  Visually inspect the alternator for signs of corrosion.
6. Engine Coupler – We strongly encourage changing the coupler along with all repowers since it requires the engine to be removed for accessibility when replacing. It isn’t worth re-installing an old coupler ontp a new enigne only to have have it fail after 20 hours of “Fresh Power”. Having to pull the engine again 20 hours later when the coupler could have been replaced much cheaper while the engine was already out of the boat.
7. SUMMARY – Evaluating the condition of the accessories is somewhat subjective however if the majority of the accessories appear to be in good condition, repowering with a new longblock could be a very good consideration.

Part 2 – Inspection of the Base Engine
READ MORE (select link)

Reference Articles
MARINE CORROSION
MARINE REPOWERING TERMINOLOGY

Topic: Boat Repowering (Part 2)

Question #1: My 2010 Model Mercruiser SR 383 Mag Marine Engine Feels Down on Power. How Can I Check The Condition of the Engine?

Response: The quick and easy answer is to perform a compression test, however this is not always the best approach as it only paints a portion of the picture to the overall condition of marine engines. We recommend performing a compression test as well as a cylinder leak down test.

Findings: After performing a quick compression test we noticed cylinder #6 registered 0 psi compression. Performing a leak down test we determined this cylinder had significant leak down through the valvetrain. This was determined by verifying that the leakage was passing through and out the intake manifold. The leak down test also revealed that although cylinder #5 had a good compression reading, it also excessive leakage. This leakage was verified to be passing through the crankcase which indicated the leakage was passing by the rings.

Conclusion: The engine run time below indicating that the engine was not run over 4,000 rpm suggested the boat was not propped according to the manufactures specification of 4,800 – 5,200 rpm. Valve “tuliping” is a sure sign of a boat being over-propped. An overloaded engine will cause excessive cylinder pressures and heat, which typically results in the intake valve deforming and losing its seat/seal. NOTE: THIS IS THE DIRECT RESULT FROM RUNNING TOO LARGE OF A PROPELLER. READ MORE on how to select the correct propeller.

Helpful Hints:
Due to standard engine clearances and normal wear, no cylinder should be expected to maintain a perfect no-leak reading.  It is important that all cylinders have a relatively constant reading both with regards to a compression and leak down tests.  A difference of 5 psi leak down between cylinders and +/- 10% compression is satisfactory. A difference of 10-15 psi leak down indicates the need for further investigation.

By listening or looking for the following, the cause of low pressure can be determined:

Air escaping from Crankcase Breather/Oil Fill Hole on Valve Cover…..Defective Rings or Worn Cylinder Walls

Air escaping from Exhaust System…..Defective Exhaust Valve

Air escaping from Throttle Body/Carburetor…..Defective Intake Valve (Tuliped Intake Valve)

Air escaping from Cooling System…..Leak in Head Gasket or crack in Block or Head