1980/03/03 Caterpillar

Connecting Rod Changes And Replacement Information{1218}


3406, 3408, 3412 Engines

An article "Wider Connecting Rods Have More Bearing Area" in the November 5, 1979 Service Magazine, and earlier articles give information about new connecting rods used in 3406, 3408 and 3412 Engines. A series of three new types of connecting rods have been released, and information about which of these are adaptable to earlier engines has not been clearly understood. This article gives an explanation of the differences in design of the three types of rods, and more details about the use of each type for service replacement. This will make the correct selection of replacement connecting rods easier.

The three different types of connecting rods used in 3406, 3408 and 3412 Engines are as follows:

NOTE: 3408 Engines with precombustion chambers do not use the third type except for service replacement, as shown in the chart.

... Straight Side. The first type has straight sides around the piston pin bore.

... Narrow Taper. The second type has a narrow (6°) taper at the top around the pin bore.

... Wide Taper. The third type has a wide (9°) taper at the top around the pin bore.

The first (straight side) and third (wide taper) types of connecting rods have the same weight and can be mixed in the same engine. The second (narrow taper) type connecting rod has a different weight, and must not be mixed with either of the other types. For this reason, the earlier (straight side) rod assemblies are canceled and the latest (wide taper) rod assemblies are used for replacement, but the second type (narrow taper) rod assemblies are still available for parts service. See the chart.

Because of the differences in piston design:

... Installation of "wide taper" rod assemblies as a replacement for "straight side" rod assemblies will not give all the advantages of the design. The reason for this is that the pistons for the "straight side" rods do not have the added bearing area around the piston pin.

... The "wide taper" rod assemblies can be installed in place of "straight side" rod assemblies, but not in place of "narrow taper" rod assemblies. This is the reason for use of 8N1728 Connecting Rod Assemblies as a replacement for the canceled 4N390 Connecting Rod Assemblies in earlier 3408 Engines with precombustion chambers (PC), but not in later 3408 Engines (PC). The later 3408 Engines (PC) use "narrow taper" rod assemblies. Only the 3408 Engines with direct injection (DI) have pistons for the 8N1728 Connecting Rod Assemblies.

In the identification of connecting rods, be sure to use the assembly part number which is put on the bottom of the connecting rod cap with a 3.18 mm (.12") high stamp. Do NOT use the forging number which is shown on one side of the center section of the rod. Since the same forging is used to make different connecting rod assemblies, use of the forging number as a reference can cause errors.

Caterpillar Information System:

1980/03/03 Spacer Plate Block Group Used For Parts Service Of Block Group With Counterbore Design{1101,1201}
1980/02/25 Identification Of Fuel Injection Lines And Nozzle Bodies For Different Combustion Systems{1252,1254}
1980/02/25 Drawings Available For Six Tools Used During Repairs Of Damaged Pin Bores In Two-Piece Booms{6501,0665}
1980/02/25 Plunger Movement Must Be Adjusted When New Rack Shut-Off Solenoid Is Installed{1259}
1980/02/25 Stronger Braces Used Between Air Cleaner And Engine{1051}
1980/02/25 Revision Of Special Instruction Form No. SMHS7267, "Use Of 5P8709 Tool Group For Alignment Of Piston Cooling Jets" Has Important Changes{1307}
1980/02/25 How To Check Operation Of Hydramechanical Shutoffs On D379B, D398B, D399 Engines{7418}
1980/02/11 Use The Correct Water Temperature Contactor{1350,1100}
1980/02/11 Warning: Avoid Use Of Fuel Mixtures Of High Volatility. If You Are Exposed To Such Mixtures, Be Aware Of The Hazards Involved And Take Proper Precautions{1280}
1980/02/04 Real Value Available Through Caterpillar Remanufacturing Programs{0374}
1980/02/04 Change To Gear On Accessory Drive Shaft Assembly Gives Longer Service Life{1207,1206}
1980/02/04 New Cylinder Liner Has Improved Design To Keep Liner Temperatures Lower{1216}
1980/03/03 Fuel Heaters Are Now Available For Field Installation{1296}
1980/03/24 Inspect Regulator Cover Assembly When Overcooling Is A Problem{1350,1380}
1980/03/24 Crankshaft Rear Seal And Wear Sleeve Are Now Serviced As A Group Instead Of Separate Parts{1161}
1980/03/24 New Top Piston Ring Has Plasma-Coated Face{1215}
1980/03/24 8S2252 Carbon Seal Tool Can Be Adapted For Use On 8N7001 Fuel Nozzle Assembly{0611,1254}
1980/03/24 Different Water Temperature Regulators Now Used To Prevent Overheating{1355}
1980/03/24 Visual Inspection Of Main And Connecting Rod Bearings{1203,1219,1230}
1980/03/24 New Fuel Injection Lines And Clamps Prevent Stresses And Contact Which Can Cause Leakage{1252}
1980/03/24 An Increase In Engine RPM Will Extend Vanes In Hydraulic Oil Pump To Start Pump Output{5055,5068}
1980/03/24 New Plugs And Rubber Stoppers For Machines With Sealed And Lubricated Track{4169,4170,4175,0622}
1980/03/24 New Control Valve Body{1155,1159}
1980/03/24 Different Vibration Damper Now Used{1205}
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