When the cylinder head in your diesel engine reaches the end of its useful life, you have an important decision to make.
You have two options:
The first option you have is to take your worn cylinder head to a machine shop and have them replace some of the broken/worn components. This includes things like valves, valve guides, valve seats, and injector sleeves. If the actual head is cracked, the shop will likely do some welding to fix it. Many diesel engine owners find this option rather attractive due to its low cost but they need to ask themselves how long they are going to keep their engine. A rule of thumb is if the engine has less than 500,000 miles or the intention is to replace the unit within 300,000 miles of the repair, this option may be applicable. If the goal is for it to last another million miles, they should consider purchasing a remanufactured cylinder head. From a performance and longevity standpoint, repairing a cylinder head presents a number of problems.
Let’s examine a few of them:
Wear: With engines today operating for a million miles or more before their first rebuild, the parts in the cylinder head are simply worn out. The problem with replacing some of the parts and performing a quick fix is that the cylinder head simply won’t withstand the wear and tear it faces from normal activities. Checking and replacing only the pieces that are out of specification almost insures the cylinder head will not last for another million miles. The reason for this is that even though a part is in specification for its measurements, it still has gone through countless
heat cycles and been subjected to numerous stress risers that will lead to a failure.
Cracks: In many instances, machine shops don’t do a very good job welding cracks on the head and a few months after the engine is up and running, the same exact thing happens again. Many machine shops don’t have the necessary equipment to properly repair a cylinder head and as a result, structural integrity and performance are compromised. There’s a reason many vendors offering this service carry heavy disclaimers.
Poor inspection: The tooling required to properly inspect a cylinder head and associated parts is getting more advanced. Not that long ago the first life of an engine was in the 500,000 – 750,000 mile range. The tolerances on the parts were not near what they are today. A good pair of calipers was all that was needed to check most pieces. Nowadays, tools such as ultrasound and eddy current machines are being used to check the surface, sub-surface and internal metal structure of parts to insure they will last. The price of these machines puts them out of reach for many repair facilities.
The second option when it comes to your cylinder head is to purchase one that has been remanufactured. The key here is to find a cylinder head that has actually been remanufactured. The terms rebuilt, reconditioned, refurbished, repaired, etc. all seem to get lumped in this category. However, a remanufactured cylinder head is one that goes through all the steps that it did when it was new at the factory and maybe even a couple more. These steps typically include: casting, machining, pressure testing, cleaning, and installation of new parts. For owners that are near or over the million mile mark and rely on their engine, this is your best bet.
Casting vs. welding: Cracking of the cylinder head is the number one cause for replacement. In the remanufacturing process, the head is recast rather than welded. This is done by cutting out any bad section of the cylinder head. The head is then heated to red hot molten temperatures and new metal is poured in. This meets the original specifications of your engine and is much stronger than welding, so you don’t have to worry about cracks opening back up.
New parts: Every single component (e.g., valves, guides, seats, springs, keepers, injector sleeves) is replaced (whether it’s worn or not) to ensure that every part works like the day the engine was new. This is a large factor of why remanufactured cylinder heads have a higher cost.
Warranty: Remanufactured heads will typically carry a much better warranty than a rebuilt head. This is because the inspection and repair processes are more thorough and all new parts are installed. Most importantly, remanufactured heads many times will carry a labor and progressive damage warranty whereas a rebuilt head will not.
A lot of owners are initially drawn away from this option because it costs more than replacing the worn parts and fixing the head, but over the course of time, the money saved by avoiding breakdowns and not having to continually bring your engine in to be repaired is well worth the investment. If you’ve already put a million miles on your diesel engine and you’re looking to put another million on it, this is the option for you.