CAT 3406 engine spare parts: 3406B, 3406C and 3406E

AMS Parts · Caterpillar engine guide

The Caterpillar 3406 is one of the most recognised diesel engines ever built. A 14.6-litre inline six produced from 1973 through to 2007, it served as a truck, marine, industrial and generator engine across a 35-year production run, and its worldwide population ran to several hundred thousand units.

That longevity is exactly why sourcing parts for one needs care. A "3406" can be any of four quite different engines, and the differences between them are not cosmetic — they run from fully mechanical injection through to full electronic control. Ordering against the model name alone is the most common way to end up with a part that does not fit.

This guide explains the generations, what separates them, and how to specify parts correctly.

What is the Caterpillar 3406?

The 3406 is the inline six of Caterpillar's 3400 family, sharing its architecture with the V8 3408 and the V12 3412. It displaces 14.6 litres (893 cubic inches) from a 137 mm bore and 165 mm stroke, and was built in naturally aspirated, turbocharged and turbocharged-aftercooled forms depending on rating and application.

In generator service the 3406 typically covers roughly 200–400 kW. In marine and industrial applications ratings vary more widely, with high-output 3406E builds reaching considerably further.

What is the difference between the 3406A, 3406B, 3406C and 3406E?

This is the single most important question when sourcing 3406 parts, because the four generations differ fundamentally in how fuel is delivered and controlled.

3406 and 3406A (1973–1987). The original. Fully mechanical, with mechanical unit injection and mechanical governing. Simple, field-serviceable and entirely independent of electronics.

3406B (1987–1993). Still fully mechanical, with improvements to the injection system and internal components over the A.

3406C (1993–1998). Largely mechanical but with an electrically controlled fuel pump on later builds, depending on production year. This makes the C a transitional engine, and it is the generation where identifying the exact build matters most — two engines both badged 3406C may be configured differently.

3406E (1993–2007). Fully electronic, running Caterpillar's ADEM electronic control with electronic unit injection. This was by far the most produced version.

Caterpillar skipped the letter D in the sequence, which occasionally causes confusion when people assume a 3406D exists. It does not.

Are 3406E and C15 parts interchangeable?

Some are, many are not — and this trips people up regularly. The C15 succeeded the 3406E in 1999 and inherited a good deal of its architecture, which is why suppliers often list a part as fitting both. But the C15 is a 15.2-litre engine against the 3406E's 14.6 litres, and the internal dimensions differ accordingly. Treat any cross-listing as a starting point to verify, not as confirmation. Always check against the serial number prefix before ordering.

Why does the serial number prefix matter on a 3406E?

The 3406E was produced under several serial number prefixes, and they denote real differences in internal components and calibration rather than just build dates. Prefixes including 5EK, 6TS, 1LW and 2WS cover changes to piston design, internal components and calibration across the production run. A part listed for one prefix may not suit another, which is why the prefix is the first thing we ask for on any 3406E enquiry.

Where is the 3406 still in service?

The 3406's production volume means it remains widespread decades after the last units were built:

In generator service the mechanical generations are often valued precisely because they are mechanical — no ECM to become obsolete, and any competent diesel engineer can diagnose and repair them. That characteristic keeps a lot of 3406 plant working long past the point where an electronically dependent engine of the same age would have been retired.

• Standby and prime generator sets, particularly in the 200–400 kW band
• Marine propulsion and auxiliary power on smaller cargo, supply and fishing vessels
• Industrial power units and pump drives
• Oilfield and drilling support equipment
• Irrigation and agricultural pumping installations
• Legacy on-highway and heavy haulage applications

Which spare parts does the 3406 most commonly need?

Injectors and fuel system components

Fuel system parts are where generation matters most. Mechanical 3406A and 3406B engines use mechanical unit injection; the 3406E uses electronic unit injection under ADEM control; the 3406C sits between the two depending on build year. Injectors, fuel pumps and governor components are not interchangeable across these generations, and fitting the wrong type is not a matter of degraded performance but of the engine not running correctly at all.

Piston, liner and ring sets

Piston and liner specification varies by generation and by serial number prefix, particularly across the 3406E range where piston design was revised during production. A matched set should always be quoted against the prefix rather than the model, and the compression ratio for the specific build confirmed before ordering.

Turbochargers

The 3406 was built in naturally aspirated, turbocharged and turbocharged-aftercooled configurations, and turbo specification differs by rating and application. A generator-rated 3406 running steady load and a marine-rated unit cycling between full power and idle will not necessarily carry the same turbo, even at similar outputs.

Cylinder heads and valve components

The 3406E uses a 24-valve overhead cam head, which differs from earlier generations. Cylinder heads are a routine overhaul item on high-hours engines, with valve seat recession, guide wear and crack detection the standard inspection points. Given the age of most 3406s still working, many heads will have been overhauled before, so cumulative machining at the face needs checking.

Gaskets and seals

A complete gasket and seal set is standard at major overhaul. On engines of this age, material degradation is not visible on inspection, so reusing apparently serviceable gaskets is a false economy that tends to show up shortly after the rebuild.

Bearings and crankshaft components

Main and connecting rod bearings, thrust washers and crankshaft components are core overhaul items. Journal wear and bearing surface condition determine whether an in-frame rebuild is viable or whether the engine needs a full strip, so these should be assessed before the overhaul scope is fixed.

Oil, water and fuel pumps

Pumps are scheduled replacement or overhaul items. On marine installations the raw water pump in particular is a high-frequency item, with impeller condition deteriorating faster than operators often expect.

How do you identify the correct 3406 part?

Start with the engine information plate, which carries the serial number. The first three characters are the serial number prefix, and that is what identifies the build generation and configuration — not the model name stamped on the valve cover.

For a 3406, we need the full serial number and prefix before quoting anything in the fuel system, the air system or the overhaul group. Model name alone is not enough to specify these correctly, and with an engine that spans 35 years of production that is not a formality.

What to send with your enquiry

Supplying the right information up front removes a round of questions and gets you a firm price faster. For any quote on this engine, please include:

Why source from AMS Parts

AMS Parts is a UK based supplier of genuine and OEM spare parts for marine, power generation and industrial diesel engines. We verify every quotation against the engine serial number rather than leaving compatibility to the buyer. Our Caterpillar engine spare parts range covers generator, marine and industrial applications, with worldwide shipping to vessels, sites and service facilities.

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