Cummins 4BT vs 6BT: What's the Real Difference for Tractors and Skid Steers?

The Cummins 4BT is a 3.9L 4-cylinder diesel, while the Cummins 6BT is a 5.9L 6-cylinder diesel. They share a family resemblance but do not use the same gasket sets. Before ordering, confirm which engine you have. Arko Tractor Parts carries Cummins gasket sets and ships nationwide from Northridge, California.

Why Buyers Confuse the 4BT and 6BT

Both engines come from the same B-series diesel family and are mechanical, durable, and widely used in industrial and equipment applications. But the 4BT is the smaller four-cylinder member of the family and the 6BT is the larger six-cylinder engine. If you order a 6BT gasket set for a 4BT, or vice versa, it will not fit.

Cummins 4BT: Compact, Strong, and Common in Equipment

The 4BT gives diesel durability in a compact package — commonly found in skid steers, compact industrial machines, construction equipment, generators, and conversion builds. Its gasket set is specific to the four-cylinder layout.

Arko carries the Cummins 4BT 3.9L head gasket kit. Use this when removing the cylinder head, replacing a failed head gasket, or refreshing the top end of a 4BT engine.

Cummins 6BT: Larger, Longer, and Built for Heavier Work

The 6BT 5.9L is one of the best-known mechanical diesel engines in North America, used in Dodge Ram trucks (12-valve era), tractors, industrial equipment, pumps, and generators. It uses a different gasket layout because it has six cylinders.

Arko carries the Cummins 6BT 5.9L 12V top head gasket set.

Which Engine Do You Have?

Confirm the engine model from the data plate — not the machine model or prior owner. The easiest field check: a 4BT has four cylinders, a 6BT has six. That simple check prevents expensive ordering mistakes.

When a 4BT Head Gasket Kit Is the Right Product

Order a 4BT head gasket kit when the engine is a Cummins 4BT 3.9L, the cylinder head is being removed, white smoke with coolant loss is present, or combustion gas is entering the cooling system. Do not use a 6BT gasket set on a 4BT.

When a 6BT 12V Head Gasket Set Is the Right Product

Order a 6BT 12V head gasket set when the engine is a Cummins 6BT 5.9L 12-valve from a 1989-1998 Dodge Ram or similar 12V application. If you have a 24-valve engine, do not order a 12-valve set.

Aftermarket vs OEM Gasket Sets

For both engines, quality aftermarket gasket sets are often the practical repair choice. Correct fitment matters more than the source. Browse the full Cummins engine parts collection.

Frequently Asked Questions

Is a Cummins 4BT just a smaller 6BT?

They are related but not the same. The 4BT is a 3.9L 4-cylinder. The 6BT is a 5.9L 6-cylinder. They do not use the same gasket sets.

Can I use a 6BT head gasket on a 4BT?

No. The 6BT gasket is for a six-cylinder engine and will not fit a 4BT.

Where can I order the right gasket set?

For a 4BT: Cummins 4BT head gasket kit. For a 6BT 12V: Cummins 6BT 12V head gasket set.