Repairing Damaged Light-Duty Diesel Engine Castings

By Gary Reed


For the sake of this article, the term “light-duty” will apply to smaller diesel engines used in pickup trucks, AG equipment, and autos with engines made by GM, International, Cummins, Kubota, Yanmar, Volvo, Mercedes and many others (up to engines with bores starting at four inches in diameter). These small bore engines were often not designed to be rebuilt and often have cast-in cylinder sleeves and valve seats.

The biggest challenge these small engines present is they often have thin walls and have a higher rate of failures during normal operating conditions. In my article in January of 2010 I covered the issues of categorizing repairs into those that crack due to accidents and those that crack under normal operating conditions. If you missed that one I strongly recommend you go to AERA’s website and read it. It outlines many types of cracks and why they happen. This information is critical to produce permanent repairs.

The first rule in repairing these castings is that you should never do anything that could damage the structural integrity of the metal or the overall casting in any way. Inappropriate welding methods are the number one reason cast iron has a bad reputation for being a cheap, weak, and difficult if not impossible, metal to repair.

The repair methods I’ll share in this article are all based on cold or mechanical ways to repair specific castings. Metal stitching to repair cracks and holes offers the most reliable and easiest ways to recondition damaged parts.

5.7 & 6.2 GM and 6.9 &7.3 Navistar cylinder heads are common examples of cracking problems due to a manufacturing process common to late model gas and diesel cylinder heads.

Induction hardening process of the valve seats in cast iron heads usually results in a very high percentage of cracked heads because the localized rapid heating and cooling results in confined expansion and contraction stress. This stress is exactly the same as the stress caused by overheating an engine and poring cold water.

These heads also share a unique manufacturing process that involves drilling a coolant passage that runs between the valve ports just below the valve seats. This frequently results in the path of the drilled hole wandering and moving from the intended position.

The drilled hole can end up very close to the intake port wall or moving upward towards the seats so that attempting to machine out a head to receive seat inserts often ends up with the seat bore intersecting the drilled coolant passage.

The following is a popular and proven method for repairing and reinforcing these heads.

By following the instructions that come with the kit part number L6265K you can repair cracks across the seats, install a brass tube inside the drilled coolant passage and install new seats if necessary even if the bore cuts into the drilled coolant passage.

With this method new seats can easily be machined or ground right over the metal stitched repair, even in a cast in exhaust seat. In the past if you cut into the seat pocket the head could not be saved. The installation of the brass tube solves this issue also. Boring and installing the brass tubes after the crack repair, cutting new seat bores and installing the seat inserts will seal off a leak caused by cutting the seat bore into the drilled coolant passage. The piloted reamer used to open up the drilled passage is carbide tipped and will easily cut off the corner of the seat insert if it protrudes into the coolant passage.

The #53 Cummins 5.9 liter diesel engines with a crack on the passenger side of the block below the core plugs has haunted many owners. These cracks are caused by a simple core shift that resulted in a very thin area that is simply not strong enough to withstand the thermal strain that develops during normal operating conditions.

In a case like this, metal stitching the crack to 100% of original strength just will not be enough to prevent future cracking. Adding the LNS reinforcement brackets has proven to be a dependable solution to this problem. We recommend adding three of them to prevent future cracks and leaks. The kit comes with everything you will need to install them. The upper part of the bracket fits into a core plug hole and seals with an O-ring. The lower part of the bracket bolts down to the block below the repair.

Repairing cracked main bearing bolt holes in engines like the 6.5 GM diesel used to be impractical or very expensive. Now with our Full-Torque thread inserts it is very easy and quick to produce a repair that is significantly stronger than new and won’t crack again. As long as the crack does not extend beyond the bottom of the original bolt hole, the only thing required to repair the threads and the cracks is the Full-Torque thread insert.

If the crack turns toward the mail bore the FT thread insert will not be enough to repair the crack and you will need to metal stitch that part of the crack (see pictures on page 42).

Small cast iron diesel cylinder head cracks are very common as I mentioned above due to the induction hardening of the seats during the manufacturing process. Because there are many very small diesel engines and to the extent we are seeing very thin walls, we can expect to see a lot of cracked heads. Installing a seat insert where there was not one from the factory has become a very popular practice however I caution you to realize that these heads will be very thin in the corner of the seat bore. This is true with both gas and diesel heads. When stitching these heads it is a better practice to stitch the crack and then cut the new seat right on the stitching pin instead of installing a seat insert whenever possible. Our stitching pins are made of steel, not cast iron and they will not burn out or leak compression. Millions of heads have been repaired this way. So, if the old seat is serviceable avoid installing an insert.

The smaller cast iron heads are so thin they become more difficult to repair because there is just not much to work with. In these cases we use our smallest stitching pins because they have fine threads. Often the cracks will extend down into the pre-cup bore which can also be stitched.

Remember that all cracks in cast iron and aluminum parts are caused by mechanical forces. In most cases the cracks relieved the stress. So all you need to do is to seal the leak and restore or increase the strength of the part to create a durable repair. If the crack was caused by heat during the induction hardening process or by over-heating, the cracks relieved that stress and the part has relaxed.

If the cracks were caused by freezing or impact of some type, that force is gone also. If the cracks were caused by a casting problem or design problem, you will need to make the part stronger than new in order for it to be returned to its required function.Small aluminum diesel heads are also repairable by stitching but they always have seat inserts installed so the repair methods are a little different. There are cases with these heads where you can leave the seats in and actually stitch into the OD of the seats to remove and seal off the cracks. When stitching into a seat insert you should use the L4 Aluminum stitching pins. The next adjacent pin can be a C1 aluminum pins to add strength.
Gary Reed, owner of Lock-N-Stitch, has over 41 years of experience, over 20 patents and is a world renown expert in the field of casting repair. For more information, call (209) 632-2345, email, or go online: or

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