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How to Correctly Swap in a Crate Engine

4BT Crated Engine

Cummins 4BT 140 HP Crate Engine Strapped to Pallet

Purchasing a new 4BT or 6BT crate engine can be an overwhelming task. We understand that many customers don’t think about engine replacement until something goes wrong. One day you’re out clearing land in your skid steer or hauling cargo around town in your Step-Van and boom.. a rod goes right through the block. The good news is we can step you through the process and get you back to work as painlessly as possible.

One the engine is purchased that is only half the battle. Installing or swapping in the engine is where the magic happens. However, it is important to get the right fit before the engine is even delivered. We try our best, here at Big Bear Engine Company, to match up one of our Cummins 4BT (3.9L), 4.5L, 6BT (5.9 L), ISB (6.7 L), ISC (8.3L) or CAT 3306DI models to what you currently have in place. Doing a “like for like” swap is always the best option.

Determining Current Needs and the Matching Engine Serial Number

The first step is determining what happened with your engine. Although our sales team are not on-site diagnostic experts, we can paint a picture of what is wrong with the engine more times than not over the phone/email. If only the cylinder head got hot or a few pistons are scored than maybe only the cylinder head needs to be replaced. If the engine dropped a valve and damaged the head, pistons and connecting rods; most likely the whole engine seized up and needs to be replaced. If the crankshaft spun a rod or main bearing or there is a hole through the block than the engine is toast! You don’t want to spend more money than you need to so it is important to do your due diligence with your mechanic.

CAT 3306DI Crate Engine Wrapped Up

CAT 3306DI Crate Engine Wrapped Up Ready For Shipment

The second step is matching up your engine serial number, critical parts list (CPL) and/or arrangement number. Once you provide your current ESN we can either plug that into Cummins Quickserve or CAT SIS and unravel the entire history and build specifications of your engine. Each make and model are different. A CAT 3306DI is not the same as a CAT 3306PC. We will look at the cylinder head, engine block, piston and fuel system configurations to determine if they match to one of our engines. Many times legacy engines/parts will cross over to new part numbers; therefore it is important really dig deep into the build sheets to make sure newer model crate engines will work with your application.

If the customer’s engine is determined to be a good fit for a crate engine we can ship with no problems. If the customer’s application is slightly different we can make recommendations on what is the best option. Sometimes a longblock only is the best option because to many variations exist. A customer can then swap over their ancillary parts (water pump, oil pump, turbo, injectors, etc...) and make the hybrid engine work with their existing application. With Cummins 4BT Engines we sell them in 105 HP, 130 HP and 140 HP models. We have seen customers with Cummins 4BT 116 HP Genset Applications, 87 HP Case Skid Steer, and even Cummins 4BT Marine 100 - 250 HP Applications. In cases where the Horsepower and Torque Ratings are less than the models we offer we can recommend going up in Horsepower only if the customer is aware modifications might be needed during the swap. For example, generator applications have a governor to keep the RPMs constant. Marine Applications require specially rated marine parts to prevent corrosion and fire hazards.

Parts Compatibility Issues

SAE Bellhousing Guide

SAE Bellhousing Guide Courtsey of Mer Equipment

Other issues you might run into with swaps is making sure the flywheel and flywheel housing will bolt up to the application. Cummins 4BT Engines are regarded as “universal” because they will attach to just about any application. There are many OE and Aftermarket Adaptor Kits available to mount up to most transmissions. Cummins 4BT Engines are built with the SAE #3 Housing which is pretty universal to all sorts of applications. Ford and GM make the most common adaptor kits are found on any number of 4BT used engines. Cummins 5.9 L / 6BT engines either come with SAE # 2 or SAE # 3 Flywheel Bellhousing.

Lastly the customer has to make sure there is enough room in the application to accommodate the engine. The Cummins 4BT is regarded as the biggest diesel engine that can fit in Jeeps, Land Cruisers, Ford Broncos and most legacy vehicles. If you are doing a 4BT Jeep Swap into a 1955 Chevy Pickup you better make sure it will fit. Newer trucks (1980 – Current) like Dodge Ram, Ford F150 or Chevy Silverado’s have bigger chassis making both a 4BT, 6BT or ISB 24 Valve Swap Possible. Cutting and welding back part of the chassis frame sometimes is necessary to make engine swaps work. We’ve even seen CAT 3126 or C7 engines swapped into automotive trucks. In fact Caterpillar engines in Ford Trucks are quite popular in Mexico even to this day.

Other considerations in terms of room also include top mounted or side mounted turbos configurations. The Cummins 4BT Models come with both side and top Holset HX30 Wastegate Turbo mounted applications. We’ve seen customer's with top mounted turbo configurations order side mounted engines much to their chagrin. Engine crossover tubes and inlet/outlet piping can also prove

SAE Bellhousing #3

SAE Bellhousing #3 Fits Cummins 4B, 4BT, 4BTA, 6B, 6BT, 6BTA Applications

to be an unexpected hindrance in terms of space once the engine is installed. Customers always find a way to make it work however sometimes swaps require some intensive labor modifications. Fuel pumps also throw a monkey wrench into the equation. Mechanical Inline Fuel Pumps like the Bosch A or P-7100 Pumps vary in terms of size, configuration and application from the larger Bosch VE or VP Rotary Style Pumps. Integrating a completely different fuel system will often require modification work to be done to the gear housing and valve cover.


Cummins 4BT Dimensions:
• 140hp : 25 x 26 x 34”, peak torque 370 ft lb @ 1500rpm

• 130hp : 25 x 26 x 35”, peak torque 280 ft lb @ 1500rpm

• 105hp : 26 x 26 x 36”, peak torque 243 ft lb @ 1500rpm


CAT 3306 Dimensions:
• 220hp : 80 x 44 x 60”, peak torque 585 ft lb @ 2300rpm

Crate Engine Electrical System and Chassis Compatibility

We also see customers who wish to put off-road rated industrial engines into automotive applications. Keep in mind that a QSB 4.5 L is different than an ISB 4.5 L. 24 Volt electrical systems, oftentimes found in large industrial equipment like dozers and excavators are not the best fit with 12 Volt on-road rated engines and vice versa. A 12V and 24V system will work however it won’t be the most efficient power supply to ancillary components of the engine.

Swapping in a diesel engine into an automotive application can be loads of fun but keep in mind that a significant amount of modifications will need to happen. The Cummins 4BT for example is roughly 800 lbs. and will require modified motor mounts, vibration dampers, upgraded axels and shocks, differentials, u-joints and adapter plates for your transmission. It is also important to know what horsepower and torque your transmission is rated for. Look for the nominal torque rating to determine if your old transmission can handle the power output specs of your new engine Check out these popular modifications to upgrade your horsepower and torque on your new Cummins 4BT or 6BT.

“Non-Like for like” crate engine swaps rarely just happen easily and will require some work to make your new diesel engine fit in your application. The good news is we have every resource available to help you make the best decision for your swap project. In fact we have written a second article which goes into more depth on how to properly research and buy a crate engine. At the end of the day most swap projects, whether it is a used, reman or surplus crate engines, go just fine with a little bit of finesse. It is best not to sweat the small set backs and just enjoy the process. Once you look at your project as a journey to learning everything about your new engine you'll find engine swaps are actually a lot of fun.

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