Introduction

When the words "use again" are in the description, the specification given can be used to determine if a part can be used again if the part is equal to or within the specification given, use the part again

When the word "permissible" is in the description, the specification given is the "maximum or minimum" tolerance permitted before adjustment, repair and/or new parts are needed.

A comparison can be made between the measurements of a worn part and the specifications of a new part to find the amount of wear. A part that is worn can be safe to use if an estimate of the remainder of its service life is good. If a short service life is expected, replace the part.

This manual contains general, operation, maintenance, troubleshooting and disassembly and assembly information.

Illustrations guide the operator through the correct procedures of checking, starting, operating and stopping the marine transmission.

Operating techniques outlined in this publication are basic. Variations in this procedure can occur with installation.

Your safety and the safety of others depends upon care and judgment in the operation of this equipment. A careful operator is good insurance against an accident.

Some illustrations and photographs in this publication may show details or attachments that may be different from your installation. Also, guards and covers may have been removed for illustrative purposes.

Continuing improvement and advancement of product design may have caused changes to your marine transmission which may not be covered in this publication.

Whenever a question arises regarding your marine transmission, or this publication, please consult your authorized Caterpillar dealer for the latest available information.

Marine Transmission Identification

Marine transmissions are identified by part numbers, gear models and input/output shaft direction of rotation.

This information is shown on the information plate located on the marine transmission.

Ordering Parts

Quality replacement parts are available from authorized Caterpillar dealers throughout the world. Their parts stocks are up to date and include all parts normally required to protect your investment in these products.

When ordering parts, your order should specify the marine transmission serial number, type (model number), direction of output shaft rotation and quantity. If in doubt about the marine transmission number, please provide your dealer with a complete description of the needed item.

Preventive Maintenance And Troubleshooting

Frequent reference to the information provided in this manual regarding daily operation and limitations of this equipment will assist in obtaining trouble free operation. Schedules are provided for the recommended maintenance of the equipment.

In the event a malfunction does occur, a trouble shooting guide is provided to help identify the problem area, and list information that will help determine the extent of the repairs necessary to get a unit back into operation.

Lifting Bolt Holes

Most marine transmissions have provisions for attaching lifting bolts. The holes provided are always of adequate size and number to safely lift the marine transmission.

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These lifting points must not be used to lift the complete power unit. Lifting excessive loads at these points could cause failure at the lift point (or points) and result in damage or personal injury.

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Select lifting eye bolts to obtain maximum thread engagement with bolt shoulder tight against housing. Bolts should be near but should not contact bottom of bolt hole.

Description And Specifications

MG-5050 Marine Transmission-Rear View
(1) Rotation indicator. (2) Front housing. (3) Oil gauge. (4) Breather and oil filler hole. (5) Selector valve assembly. (6) Oil outlet to heat exchanger. (7) Instruction plate. (8) From heat exchanger. (9) Oil drain plug. (10) Filter screen cover.

General Information

The MG 5050SC is a reverse and reduction marine transmission, which offers conical helical gearing for quieter operation currently available in the following ratios: 1.16:1; 1.53:1; 1.71:1; 2.04:1; 2.45:1 and 3.00:1. This transmission is controlled completely by hydraulics (See Illustration C36993P1). Both the forward and the reverse clutches are operated by main pressure oil supply. The bearings, clutches and gears are lubricated and cooled with low pressure oil.

(A) Right hand engine. Starboard rotation propeller. (B) Left hand engine. Port rotation propeller.

NOTE: Use configuration A and B for twin screw installation with opposite propeller rotation. Configuration A is preferred for single engine installation.

When shipped from the factor, each unit is designated for use with a particular engine rotation. Within their rated capacities, these units may be operated continuously in either forward or reverse. The unit can be adapted to either left hand or right hand engine rotation. To adapt to the opposite engine rotation, remove the oil pump and gasket and replace them with the pump and gasket for the desired rotation. For a right hand engine rotation use oil pump number PX-8757. For a left hand engine rotation use oil pump number XB-5595-A.

Direction Of Drive

The forward (input) clutch shaft and driving transfer gear always rotate in the engine direction. The reverse clutch shaft and driven transfer gear always rotate opposite engine rotation because the driven transfer gear is meshed with the driving transfer gear on the forward clutch shaft. When the forward clutch is engaged, the forward input pinion rotates in the engine direction. The output gear, which is installed on the output shaft, is meshed with the forward input pinion and the output gear and shaft are driven opposite engine rotation. When the reverse clutch is engaged, the reverse input pinion rotates opposite engine rotation. The output gear is meshed with the reverse input pinion and, therefore, the output gear and shaft are driven in the direction of engine rotation.

Construction Features

The driving and driven transfer gears and output gear are mounted on keyless tapers.

The MG5050SC housing consists of an SAE 1, SAE 2 or SAE 3 front housing and front and rear half housings. They are sealed together with an anaerobic plastic gasket compound.

The forward, reverse and output shafts have taper roller bearings which require shims to adjust endplay of the respective clutch shaft.

The oil pump is tang connected and driven by the reverse clutch shaft.

Oil is directed by the control valve through drilled passages in the forward and reverse clutch shafts to orifices through which the front and reverse clutch shafts are lubricated. There are also orifices in the shafts through which both clutches are cooled.

The transmission has an oil strainer mounted on the inlet side of the oil pump. The strainer is in the suction line between the sump and oil pump in the hydraulic circuit.

Lubricant Pressures And Requirements

Oil Pressure Check Points
(1) Oil in from heat exchanger. (2) Valve inlet pick-up point. (3) Forward Clutch pick-up point. (4) Lube oil pressure pick-up point. (5) Reverse Clutch pick-up point. (6) Lube oil pressure pick-up point. (7) Manifold and selector valve assembly. (8) Oil pump. (9) Screen filter cover. (10) Oil drain plug. (11) Oil out to heat exchanger.

The following chart gives oil pressure at different speeds and ranges using a 2075 kPa (300 psi) spring.

NOTE: Trolling valve with cam at minimum trolling stop position is 900 rpm.

NOTE: The oil capacity is 2.7 Liter (.71 U.S. gallon) plus volume in hoses and heat exchanger.

NOTE: Multi-viscosity oils such as 10W-20W should not be used in marine transmissions. Use only SAE-API service class cd engine oil certified to meet TO-2 transmission oil specification or type C-3 transmission fluid. Also approved is SAE-API service class CC engine oil.

NOTE: Check oil level every 10 hours. Change oil and clean filter screen every six month or 1000 hours of operation, whichever comes first. Drain the oil by removing the oil drain plug on the rear of the transmission.

NOTE: The oil pump capacity is 10 liter/min (2.85 U.S. gpm) at 2000 rpm and 2125 kPa (300 psi).

NOTE: The maximum input speed is 3200 rpm.

NOTE: The dry weight is 86 kg (189 lbs) excluding heat exchanger, hoses, companion flange and trolling valve.

Heat Exchanger And Requirements

(1) Zinc anode. (2) Oil in. (3) Oil out. (4) Water in. (5) Water out.

The heat exchanger is designed to maintain the oil in the hydraulic system of the marine transmission at the proper temperature by passing coolant from the engine through the heat exchanger. The heat exchanger should be installed in a location convenient to both engine coolant and marine transmission oil.

Heat exchangers used in a salt water applications, have a zinc rod (1) installed at the inlet and outlet heads. These rods must be checked every 90 days. If over 50% of the rod has disintegrated, a replacement rod must be installed to provide effective protection.

Excessive corrosion of the zinc rod indicates electrolytic action. A careful inspection should be made to determine if this action is caused by a short circuit to external grounded electric current. These conditions must be eliminated to avoid the necessity of frequent replacement of the zinc rods. If these conditions do not exist, it is evident that the corrosion is due to local electrolysis. If rods are corroded with foreign material, they should be cleaned with a wire brush.

Service Requirements

(1) Maximum velocity in fittings, pipe, hose and tubes - 7.6 m/sec (25 ft/sec).

(2) Burst pressure, minimum = 10 X peak oil pressure at heat exchanger.

(3) Hose - SAE J517 100R1 meeting USCG 46 CFR 56.60-25(C), 135°C (275°F).

(4) Protect lines from mechanical damage. Zinc anodes protect heat exchanger raw water passages from corrosion. Check the zinc anodes frequently. Replace the zinc anodes when necessary.

NOTE: To choose the correct heat exchanger, state if raw (open channel and sea) or fresh (closed engine jacket and keel cooler) water will cool heat exchanger. Give the maximum water temperature into heat exchanger, [ie. raw water 29°C (85°F), keel cooler water 60°C (140°F)]. The minimum and maximum liter/min (U.S. gpm) of water flow to heat exchanger must also be known.

Marine Transmission Component Location

Marine Transmission Right Rear View
(1) Selector valve assembly. (2) Rotation direction. (3) Oil gauge. (4) Breather and oil fill hole. (5) Front housing. (6) Hydraulic pump. (7) Output shaft and flange. (8) Screen filter cover.

Marine Transmission Cross Section View
(1) Selector valve assembly. (6) Hydraulic pump. (8) Screen filter. (9) Driving ring. (10) Drive spider. (11) Output shaft and flange. (12) Driven transfer gear. (13) Reverse clutch. (14) Reverse pinion. (15) Forward clutch. (16) Driving transfer gear. (17) Forward Pinion. (18) Output gear.

Hydraulic System (Operation)

Forward Clutch Shown Engaged Position-Reverse Clutch Disengaged.
(1) Forward clutch. (2) High pressure regulator. (3) Control valve lever. (4) To trolling valve. (5) High pressure regulator. (6) Plugged trolling channel. (7) To sump. (8) Rate if rise piston. (9) Plate orifice. (10) Sump. (11) Reverse clutch. (12) Screen filter. (13) Hydraulic pump. (14) Heat exchanger-customer supplied. (15) Pressure gauge. (A) Sump. (B) Clutch apply oil pressure. (C) Lube oil pressure.

This marine transmission has forward, neutral and reverse positions obtained by means of the control valve. When these positions are selected, the control valve directs high pressure oil through internal passages to operate the clutches.

Oil is pumped through the system by the gear-type pump. The oil is taken from the sump through the strainer by the pump and discharged through the heat exchanger. The oil then goes to the combination control and pressure regulation valve. The oil enters the pressure regulation area of the valve where main pressure is regulated by cascading excess oil into the lube circuit. The lube oil is distributed through fixed controlled orifices to lubricate bearings and cool the clutches.

In neutral, the inlet ports to the clutches are blocked, the clutches are disengaged, and the area behind the clutch pistons is open to sump. Oil is distributed through the lubrication system.

When the control valve is shifted to engage either clutch, the control valve directs main pressure to engage the selected clutch pack. Oil is also directed through a port in the control valve stem to a fixed orifice in the orifice plate causing a controlled flow of oil to unseat the rate-of-rise piston and move it to seat on a shoulder in the pressure regulator springs. This progressively increases the clutch to engage at a controlled rate. Overage oil becomes lube oil. The control valve allows only one clutch to be engaged at a time, and the oil from the disengaged clutch is dumped to sump. When a clutch is disengaged, any centrifugal pressure head existing behind the clutch apply piston is relieved to sump through the control valve. This allows the return springs to move the clutch piston to the disengaged position to prevent clutch drag.

Control Valve Assembly

The control valve assembly contains passages and ports for the transmission and direction of pressurized oil within the hydraulic system. The pressure rate-of-rise piston within the control valve assembly provides a rapid, yet smooth, pressure rise for the hydraulic system during clutch engagement.

Control Valve (Neutral)

Control Valve (Neutral), Cutaway View.
(1) Connection to sump. (2) Control valve lever. (3) Connection to trolling valve. (4) High pressure regulator. (5) Connection to sump. (6) Piston springs. (7) Plugged trolling channel. (8) Rate of rise piston. (9) Plate orifice. (A) Passage. (B) Chamber. (C) Port. (D) Port. (E) Passage. (F) Passage. (J) Port. (K) Slot. (M) Passage.

Control Valve (Neutral), Sectional View.
(1) Connection to sump. (10) Stem. (11) Manifold. (12) Lube distributor. (A) Pressure regulator inlet passage. (B) Chamber. (C) Reverse clutch lube port (neutral position). (D) Forward clutch lube port (neutral position). (E) Passage. (F) Passage. (G) Port. (H) Passage. (J) Port. (K) Slot. (M) Passage.

Oil enters the control valve body through passage (A) and fills chamber (B). The oil causes the high pressure regulator piston to partially compress the piston springs against the rate-of-rise piston. This pressurizes the oil in chamber (B). This pressure varies with engine speed.

The movement of the high pressure regulator piston against springs (6) exposes port (C) in the valve body. Ports (C) and (D) direct overage oil to lubrication and clutch cooling system. Passage (E) (which is the engaging outlet to the reverse clutch) and passage (F) (which is the engaging outlet to the forward clutch) are interconnected by slot (K) in the control valve stem when in the neutral position. The slot is aligned with a drilled hole and cored cavity in the front face of the valve body. The drilled hole and cored cavity are aligned with drilled holes that pass through the manifold and the main housing to sump. Therefore, passages (E) and (F) are at atmospheric pressure at this time. Also, port (J) is at atmospheric pressure since port (J) inter-connects with slot (K). The area between the pistons and around the springs is vented to the sump and main housing. This area is at atmospheric pressure at all times permitting the return to sump of any leakage oil past the pistons.

Control Valve (Forward)

Control Valve (Forward), Cutaway View.
(1) Connection to sump. (2) Control valve lever. (3) Connection to trolling valve. (4) High pressure regulator. (5) Connection to sump. (6) Piston springs. (7) Plugged trolling channel. (8) Rate of rise piston. (9) Plate orifice. (A) Passage. (C) Port. (D) Port. (F) Passage. (L) Chamber. (M) Rate of rise valve discharge to sump passage.

Control Valve (Forward), Sectional View.
(1) Connection to sump. (12) Lube distributor. (A) Pressure regulator inlet passage. (B) Chamber. (C) Reverse clutch lube port (reduced flow). (D) Forward clutch lube port (full flow). (E) Passage. (F) Passage. (G) Port. (H) Passage. (J) Port. (K) Slot. (M) Rate of rise valve discharge to sump passage.

When a shift to the forward position is desired, the control valve lever is moved away from pump side position. The shift causes the control valve stem to rotate. The pressurized oil in chamber (B) is directed through passages (F) and (H). Passage (F) is aligned with a drilled hole and a channel in the manifold directing main pressure to the forward clutch. Pressurized oil from passage (H) travels through passage (M) and enters chamber (L) through an orifice in the orifice plate. The orifice in this plate meters the oil for a steady, smooth pressure rise in chamber (L). As chamber (L) fills with oil, the rate-of-rise piston moves against the piston springs until the piston is stopped by a shoulder in the valve body. This causes the pressure in chamber (B) to rise to clutch engaging pressure. When in forward, passage (E) remains at atmospheric pressure since slot (K) remains open to sump.

When a shift is made from forward to neutral, the valve stem is rotated. Under these conditions, passages (E) and (F) are connected to sump by slot (K). Passage (M) is also connected to sump by port (J) in the valve stem. Since passage (F) is connected to slot (K), oil drains rapidly from the forward clutch to sump. Since passage (M) is now at atmospheric pressure, the oil pressure in chamber (L) unseats the steel ball against the compression spring, permitting a rapid oil drain from chamber (L) to sump and allowing the rate-of-rise piston to move back against the orifice plate. The forward clutch is now disengaged and main system pressure reduced to neutral pressure.

Control Valve (Reverse)

Control Valve (Reverse), Cutaway View.
(1) Connection to sump. (2) Control valve lever. (3) Connection to trolling valve. (4) High pressure regulator. (5) Connection to sump. (6) Piston springs. (7) Plugged trolling channel. (8) Rate of rise piston. (9) Plate orifice. (A) Passage. (C) Port. (D) Port. (E) Passage. (L) Chamber. (M) Rate of rise valve discharge to sump passage.

Control Valve (Reverse), Sectional View.
(1) Connection to sump. (12) Lube distributor. (A) Pressure regulator inlet passage. (B) Chamber. (C) Reverse clutch lube port (full flow). (D) Forward clutch lube port (reduced flow). (E) Passage. (F) Passage. (G) Port. (H) Passage. (J) Port. (K) Slot. (M) Rate of rise valve discharge to sump passage.

When a shift to the reverse position is desired, the control valve lever is moved to pump side position. The shift causes the control valve stem to rotate. The pressurized oil in chamber (B) is directed through passages (H) and (E). Passage (E) is aligned with a drilled hole and a channel in the manifold directing main pressure to the reverse clutch. Pressurized oil from port (G) travels through passage (M) and enters chamber (L) through an orifice in the orifice plate.

The orifice in the plate meters the oil for a steady, smooth pressure rise in chamber (L). As chamber (L) fills with oil, the rate-of-rise piston moves against the piston springs until the piston is stopped by a shoulder in the valve body. This causes the pressure in chamber (B) to rise to clutch engaging pressure.

When in reverse, passage (F) remains at atmospheric pressure since slot (K) remains open to sump. When a shift is made from reverse to neutral, the valve stem is rotated. Under these conditions, passages (E) and (F) are connected to sump by slot (K). Passage (M) is also connected to sump by port (J) in the valve stem. Since passage (E) is connected to slot (K), oil drains rapidly from the reverse clutch to sump. Since passage (M) is now at atmospheric pressure, the oil pressure in chamber (L) unseats the steel ball against the compression spring permitting a rapid oil drain from chamber (L) to sump and allowing the pressure rate control piston to move back against the orifice plate. The reverse clutch is now disengaged and main system pressure reduced to neutral pressure.

Trolling Valve

The trolling valve contains passages and ports to work in conjuction with the control valve for the transmission and direction of pressurized oil within the hydraulic system required for trolling. The rate-of-rise piston of the control valve and the cam of the trolling valve work together to provide and maintain pressures within the hydraulic system required for trolling.

Selector Valve Assembly
(1) 1/16 NPTF plug. (2) Chamber.

The 1/16 NPTF plug (1) must be removed to allow pressure in chamber (2) to be drained to sump through trolling valve device.

Trolling Valve (Non-trolling Mode)

Trolling Valve (Non-trolling Mode)
(3) Trolling valve body. (4) Trolling stem and cam. (5) Plunger piston. (6) Seat orifice.

Trolling Valve (Trolling Mode Forward 1st/Reverse 2nd)
(3) Trolling valve body. (4) Trolling stem and cam. (7) Detent device. (8) Outlet to sump.

The trolling valve is in non-trolling mode when the cam/trolling lever is in the detent position. The trolling valve, with the cam/trolling lever in the non-trolling position, allows the valve to operate as standard control valve.

Trolling Valve (Forward Or Reverse)

When the trolling valve is to be used for either forward or reverse the cam trolling lever is moved out of the detent position and into the trolling range.

Selector Valve Assembly
(1) 1/16 NPTF plug. (2) Chamber.

Control Valve
(9) Chamber.

With the cam/trolling lever out of the detent position, the rate-of-rise piston position can be hydraulically adjusted by partially draining chamber (2) to decrease the compression of the outer, middle, and inner springs against the high pressure regulator piston decreasing the pressure in chamber (9) of the valve. With the cam/trolling lever out of detent, the trolling valve provides manual control by adjustment of trolling lever, at low pressures required for trolling.

NOTE: Be sure to observe and record marine transmission sump oil temperature. If temperature drops below 57°C (135°F) during trolling mode operation, it is recommended that a thermostatic bypass valve be installed in the transmission's hydraulic circuit.

The operator must select the trolling mode with the control valve lever in neutral and set the engine speed at or below the recommended maximum trolling rpm as stated in the oil pressure chart.

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Do not operate marine transmission in the trolling mode at engine speeds above the maximum trolling rpm. The maximum engine speed in trolling is 1100 rpm or 40% of full load engine speed, whichever is smallest. Install the pilot house instruction plate in an ara near the trolling valve control head in the pilot house where it may be easily read. Failure to obey this operating limit can result in major damage to marine transmission components, which can cause an unsafe operation condition to occur. Unsafe operating conditions could result in loss of vessel maneuvering control, vessel damage, and/or loss of property and/or life.

Power Flow

Neutral

(A) Input. (B) Output.

When in neutral, the forward and reverse shafts, transfer gears, and steel clutch plates rotate at engine speed. Other parts including the output shaft do not turn.

Forward

(A) Input. (B) Output.

In forward, the same parts are turning that were turning in neutral. When the forward position is selected, hydraulic pressure is applied to the forward clutch piston clamping the friction and steel clutch plates together. The forward input pinion will then rotate at engine speed and direction, because the friction plates are spline-connected to the pinion. Since the forward input pinion is in mesh with the output gear, the output gear and shaft will rotate in anti-engine direction. The reverse input pinion will be back-driven (engine direction) when the unit is in forward.

Reverse

(A) Input. (B) Output.

In reverse, the same parts are turning that were turning in neutral. When the reverse position is selected, hydraulic pressure is applied to the reverse clutch piston clamping the friction and steel plates together. The reverse input pinion will then rotate at engine speed and anti-engine direction, because the friction clutch plates are spline-connected to the input pinion. Since the reverse input pinion is in mesh with the output gear, the output gear and shaft will rotate in engine direction. The forward input pinion will be back-driven (anti-engine direction) when the unit is in reverse.

Back Driving

Current production marine transmissions can be back-driven (propeller windmilling with dead engine) in the following conditions provided that the vessel speed when back driving the marine transmission does not exceed the normal maximum propulsion speed of the vessel.

Intermittent Back Driving

Examples: Sail boat auxiliary - short trips, less than one day. Towing purse boats in seining operations. Twin screw vessel with operation of only one engine for part of the day. Towing home a boat with engine trouble, short trip - less than a day.

1. Start the engine and operate the marine transmission in neutral at normal fluid pressures for a minimum of four minutes, doing this once every 12 hours for Model MG 5050SC. Maintain the back driven marine transmission's oil level as for normal propulsion or use above full oil level.

2. If the engine can not be started, an alternative would be to lock the propeller shaft to prevent rotation. If it is not possible to lock the propeller shaft, plug the dipstick tube, fill the unit with oil, then pump the oil down to the recommended level.

Continuous Back Driving

Examples: Towing to deliver a boat. Towing home a boat with engine trouble, long trip. Sail boat auxiliary - long trip.

1. Prior to backdriving, start the engine and operate the marine transmission in neutral at normal fluid pressures for a minimum of four hours for Model MG 5050SC. Maintain oil level as for intermittent back driving.

2. If the engine can not be started, an alternative would be to lock the propeller shaft to prevent rotation. If it is not possible to lock the propeller shaft, plug the dipstick tube, fill the unit with oil, then pump the oil down to the recommended level.

Preventative Maintenance

General

Lubrication

All moving parts of the MG 5050SC are lubricated by the oil within the sump as it travels throughout the hydraulic system. The preventive maintenance required to keep the transmission functioning properly is slight; however, it is very important that the following directions be complied with. No other lubrication is required beyond the daily oil check.

Overhaul interval

A complete overhaul of the unit should be made at same time that the engine is overhauled. All parts showing signs of wear, fatigue, etc. should be replaced at that time.

Hydraulic System

1. Oil capacity

The oil capacity of the model MG 5050SC Marine transmission is 2.70 liters (.71 U.S. gallons) or to the 'FULL' mark on the oil level gauge. The oil used in the marine transmission should be of the same quality and type recommended by the engine manufacturer.

2. Oil level

The oil level should be checked daily. To check oil level, start engine and with gear in neutral, check level and adjust oil level at the full mark when oil temperature reaches the range of 45 to 55°C (113 to 131°F).

3. Oil and filter screen cleaning interval (maximum).

The oil must be changed and the filter screen cleaned every 1000 hours of operation or more often if conditions warrant. Boats that are placed in dry dock or storage for periods of three months or more, should have the oil changed in the marine transmission prior to return to active use.

4. Draining

Drain the transmission by removing the O-ring plug on the rear side at the bottom.

5. Filling

a. Remove the breather from the top of the main housing assembly.

b. Pour the oil through the breather opening.

c. Fill the sump with .38 litre (.1 U.S. gallon) of the correct weight oil.

d. Start the engine and let it idle with transmission in neutral until oil is circulated throughout the hydraulic system.

e. With the oil at operating temperature, transmission in neutral and the engine running at low idle, check the oil level.

f. Add oil as necessary to bring the oil level up to "FULL" on the oil gauge.

6. Oil screen filter.

Remove and clean the oil strainer at every oil change or sooner if necessary.

Periodic Visual Inspection

1. Check the mountings for tightness or damage such as cracks. Tighten loose mountings and replace damaged parts.

2. Inspect heat exchanger oil lines for leaky connections, kinks, cracks or other damage. Replace damaged lines.

3. Check pressure and temperature gauges where applicable.

4. Inspect the drive line and the input and output shaft oil seals for leakage. Replace parts as required.

5. Inspect unit nameplates for looseness and corrosion. Tighten mounting screws that are loose and replace nameplates that are corroded.

NOTE: Zinc anodes are installed in the heat exchanger to help protect it from corrosion. Remove and inspect the anodes frequently because they are consumed as they provide protection. Replace the anodes as necessary.