In-Frame vs. Out-of-Frame Kits: Which Way Is Best?

When it comes to heavy-duty diesel engines, whether for your semi-truck or construction equipment, repairs and rebuilds come with the territory. You can have all the preventative measures in the world and take excellent care of your engine, but the natural wear and tear of items mean your engine parts have a certain life expectancy.

So, once you start talking about rebuilding, you may begin to hear words like "in-frame" and "overhaul." Just as the name implies, in-frame repairs generally refer to repairs, modifications, and work that you are able to complete without removing the engine from the vehicle.

Meanwhile, a complete overhaul, sometimes known as an out-of-frame repair, indicates a need to take the entire engine out of the vehicle in order to perform a more thorough inspection and repair procedure. When it comes to in-frame vs. out-of-frame kits, you might find yourself asking, "Which way is best?” Well, today, we're going to guide you through how to know which overhaul kit you need and some of the advantages and disadvantages of each process to ensure your engine gets the best care it possibly can.

Which Kit Do I Need: In-Frame or Out-of-Frame?

Knowing which kit you need for your engine is fundamental to deciding which one is better for you. As we mentioned earlier, an in-frame overhaul kit assumes you won't be removing the engine from the vehicle. Since you won't be taking apart the front cover or removing the crankshaft, you will notice an in-frame kit omits a replacement front cover gasket.

Out-of-frame overhaul kits are generally much more involved because you typically use one of these when a critical part is no longer in working order. Failing parts like a crankshaft, dropped valve seat, or connecting rod can cause major engine damage, requiring a complete overhaul kit to make repairs.

So, before you start asking which one is best, it's a good idea to analyze the underlying problems with your engine and go from there. Even if your engine suffers from a minor issue not associated with a significant component, a complete overhaul kit may be your preference for performing full maintenance.

What To Expect from an In-Frame Overhaul Kit

Because people generally pick in-frame kits when a major part that requires taking the engine from the vehicle isn’t damaged, you may think of them as preventative. Performing maintenance on easily accessible items such as the piston rings, cylinder linings, and pins is achievable with an in-frame kit. While you may still need an out-of-frame overhaul kit down the road, investing in an in-frame kit can aid in preventing costly repairs down the road.

In-frame kits generally come with a few very specific, necessary items. You will find OEM-spec replacement pistons, cylinder liners, pins, pin retainers, and piston rings. In a more comprehensive in-frame overhaul kit, you should find crankshaft bearings and connecting rod bearings. These pieces allow you to perform basic in-frame repairs to your engine and are suitable for regular maintenance and upkeep.

When looking at in-frame rebuild kits, it's good to check if they include an oil pan gasket and an upper gasket set. The latter group should have a head gasket, exhaust manifold gaskets, intake manifold gasket, and applicable O-rings and seals for various engine types. A truly comprehensive set may also include electrical connector seals and a thermostat housing gasket, but not always.

A natural upside of the in-frame overhaul kit is that you do not need to remove the diesel engine from the vehicle during an in-frame overhaul. However, it is crucial to remember that the engine needs to be accessible from multiple angles to perform optimum maintenance.

What To Expect From an Out-of-Frame Overhaul Kit

Naturally, with an out-of-frame overhaul kit, you must remove the engine from the vehicle altogether. An overhaul is more expensive, more time-consuming, and a much larger project from start to finish. However, a notable advantage of this process is that the heavier focus allows for a much more thorough examination of the diesel engine. You are able to examine all the significant components of the engine from the head, block, and every OEM component.

One of the primary reasons for using an out-of-frame overhaul kit is when a fundamental hard-to-reach piece of the engine suffers damage. Fortunately, outside of extreme situations, vital components like the crankshaft and connecting rods are generally salvageable.

Out-of-frame kits generally come with many of the same pieces and materials as the in-frame kit. The increased cost of an out-of-frame overhaul kit is to cover the extras such as a lower gasket set and nearly every seal, O-ring, and gasket those hard-to-reach parts of your engine will require. The reason why many folks refer to the out-of-frame kit as an overhaul kit is that it's common to perform a complete overhaul of the engine.

Since you’re taking it out, dismantling the engine allows for every part to be cleaned and adequately tested. Out-of-frame overhauling is a lengthy process, but one that is vital for discovering any flaws, imperfections, or issues with the engine so those performing the task can address them adequately.

Which Kit Do I Need?

When asking which way is best when it comes to in-frame versus out-of-frame overhaul kits, there are many factors to consider. Your engine starts from the block and the crankshaft. It's a good idea to perform in-frame maintenance every 200,000 miles. If your truck goes over 700,000 miles, that's a good time to invest in an out-of-frame overhaul. Each kit is an investment, but taking precautionary measures to perform maintenance regularly may save your engine from unexpected complications in the long run.

Knowing what type of engine you’re working with and which parts work best for you are also helpful factors in deciding which kits to buy, potentially lowering expenses. If you need 3406e Cat overhaul kits, you're working with a wide operating range. Whether you need a complete kit or some replacement parts to tackle a specific problem, ATL Diesel Inc has the parts, specialists, and information you need for all your diesel engine needs. If you need in-frame or out-of-frame overhaul information, reach out to us today at or contact us by phone at 866-905-3916.

In-Frame vs. Out-of-Frame Kits: Which Way Is Best?