Click on a thumbnail to see the full-size image
What’s Hot In Cold Crack Repairs!
By Doug Kaufman
It is one of the most common ailments of a modern engine, requiring attention whenever it is discovered. It has the potential to be a great profit center, but it can also cause no end of frustration.
"It" is a crack, and whenever one is discovered in a cylinder head or engine block, it means repair or replacement. Unfortunately, discovering cracks is more common than ever, particularly in today’s newer, thin-walled castings.
With domestic cores becoming more and more scarce, some engine rebuilders may look to alternative sources for cores. "You can’t rebuild an engine unless you have cores, and they’re getting almost impossible to find," says David Diperstein, president of Seal-Lock International. "Yet, even some of the replacement cylinder head cores shops are getting are coming in with cracks. Salvage of castings is becoming vital."
The Chevy 350, the Ford 2.9L V6 and other engines are notorious for cracking, say engine rebuilders and manufacturers of crack repair materials. In fact, almost any cast iron or aluminum gasoline or diesel head or block can develop cracks, so learning and using appropriate repair techniques is imperative.
"Today’s engines are so thin, we’re doing crack repair in 1/8-inch thick material," says Gary Reed, general manager of Turlock, CA-based Lock-N-Stitch. "Half of our engines are failing under normal conditions because of light walls. Take the light walls and the induction-hardened exhaust seats which cause the crack, and we’re seeing failure numbers that exceed 50%. It’s getting to the point where an automotive repair shop can’t stay in business without fixing cracks."
According to Bill Sterback, director of engineering at Recon, Automotive Remanufacturers, Inc., Philadelphia, PA, repairing cracks is usually an unavoidable step in the process. "Especially with aluminum cylinder heads, we’re doing some heavy duty crack repair. At least 30% of what we do has to go through a major repair. It’s much more prevalent than it used to be," says Sterback.
Recon rebuilds approximately 250 engines per day, Sterback says, including gasoline, light diesel, high performance and marine. "On average, we probably pin 50 heads per day."
No heat needed
Pinning, plugging or metal stitching are all words to describe the method of repairing cracks in cast engine components without the use of heat. While definitely not a new practice, recent significant advancements make cold crack repairs easier and more reliable than ever before.
"If a shop expects to make money fixing cracks, they’re going to do it cold," explains Lock-N-Stitch’s Reed. "I’ve welded cast iron for years, still do welding in our shop and still teach it. But I will not weld an automotive cylinder head — there’s no money in it."
According to Reed and Seal-Lock’s Diperstein, cast iron welding in the shop makes little sense for several reasons, not the least of which is time, cost and welder experience. Because of the properties of cast materials, they are very difficult to weld properly, and improper welding leads to further cracking. Cast iron must be heated sufficiently and cooled slowly to take a weld properly.
"The place everyone gets into trouble with welding cast iron is they weld it too cold," says Reed. "If the weld cracks, it was done too cold. If the metal gets hard, it cooled too fast — simple as that. And, if cast iron cools too fast, it gets so hard you can’t machine it."
Without getting into advanced metallurgy, understand that in order for a weld to actually become part of the head or block, the metal around it must stretch as well. The weld material contracts as it goes from a liquid to a solid state, and the surrounding metal must stretch to let it do that.
The most common mistake that people make when attempting to weld cast iron is they fail to realize that it is the heat applied to the casting that determines the outcome and not the type of welding rod, wire, powder or method used. It’s all about the heat. Electric welding cools too fast. Oxyacetylene welding procedures perform the best but require preheating from 1,000° to 1,500° F, followed by a very slow cool down. Proper stress relieving takes place as the weld cools slowly between 1,800° and 1,200° F.
Welding can be successfully employed for repairing ears or corners of cylinder heads, says Reed, but not for engine blocks. It’s a skill that takes time to learn to do properly. "It takes years, literally, to learn to be a cast-iron welder — welding every day on an assembly line," says Reed. An automotive repair shop is not going to do that. They need something they can do quickly and get out the door."
Rick Geertsema, vice president and general manager of Excelsweld in Oakland, CA, explained the difficulties of welding in an article in the April 1996 issue of Automotive Rebuilder ("Turning Cracks Into Cash,"). In that article, Geertsema detailed the steps necessary to do welding correctly. "If it was easy, everybody would be doing it," he concluded.
Contacted for this article, he says his shop still does a great deal of welding — more than ever before, as a matter of fact, because there are so many fewer welders out there. "I’m the cast iron welder here," Geertsema chuckles. "In the 10 years I’ve been with the place, only one guy has asked me to teach him how to do it. They just don’t seem to have any interest in it anymore."
Welding cracks in cast aluminum, too, requires a special touch; one that Geertsema says isn’t easy to come by. "We brought in a guy who had spent two years learning to weld — had become a certified welder, in fact. He’d also worked in a fabrication place for a year, so he knew how to weld aluminum. But every head he welded leaked. It took him about six months to learn how to weld so the heads wouldn’t leak."
Pinning, on the other hand, offers that quick repair technique that, from all reports, is a cost effective, permanent repair, requiring minimal technician expertise and almost immediate payoffs. Not that it is foolproof and perfect for every situation, but pinning can offer significant profit potential.
"Crack repair can be the biggest profit maker in the shop," says Seal-Lock’s Diperstein. "And any cast iron or aluminum component that you can reach with a drill bit and tap and is at least 1/8-inch thick, can be repaired by pinning."
The original "pin," says Geertsema, was simply a tapered rod that was driven into a tapered hole drilled through a crack. Used to repair freeze cracks in Ford trucks during the 1920s, it likely was adapted from the repair practices used to fix cracks in large industrial presses and equipment.
The theory of the tapered pin was that it would expand the crack as far as it possibly can. The stresses of the metal are then trying to close back on the pin because it is being pushed apart so hard. Years later, Irontite began putting threads on these rods to offer additional holding power in the crack. Today, there are three main suppliers of pinning products: Irontite (recently purchased by Kwik-Way Inc., Marion, IA), Seal-Lock International, Dresher, PA, and Lock-N-Stitch, Turlock, CA.
The metal expansion mentioned by Geertsema is known as "radial spreading pressure," and, according to Reed, occurs anytime a standard threaded fastener is used in a crack repair procedure.
"This pressure is acceptable as long as the casting has enough structural integrity to contain the pressure. An example is the combustion chamber of a cylinder head, because they are strong structural shapes," he explains. "With the complex geometry of metal in the combustion chamber, you can tighten the pins in without overstressing the crack site."
A different situation is a crack running along an edge of a casting or into a core plug hole on a block, says Reed. Without the structural strength, a standard threaded fastener may not be appropriate.
"Once you start screwing the pins in and tighten them, you develop what’s known as ‘cumulative spreading pressure’ — each one picks up where the last one left off. So every one you add puts more force against the sidewall of the crack, defeating the advantage you’re trying to achieve.
"We prefer to call the type of repair we do as stitching’ rather than ‘pinning,’" says Reed. "We’ve taken the concepts of both automotive repair and industrial repair and refined them into a premium technology."
Lock-N-Stitch’s solution is the Castmaster pin. Developed in 1993, this specialized fastener at first glance looks similar to a standard straight pin, but features a Spiralhook thread pattern that actually ties the metal back together
"The threads all point in an upward direction," explains Reed. "On this fastener, the angle of the bottom of the thread is 45 degrees, but the top side of the thread is a negative 20 degrees — it’s actually a hook. The shoulder on top of the pin overhangs the threads and has a reverse angle under it. When you tighten it, the shoulder seats into a matching machined counterbore, pulling up on the threads and creating radial drawing pressure. We literally reverse the forces of the spreading pressure, drawing the metal together."
Further spreading of the crack has been a problem since the development of the pinning process, says Reed. The industrial world dealt with spreading by placing locking devices across the crack, which would create a grip and develop holding power across the crack.
"The problem is," Reed says, "that locking devices require a flat surface — you can’t wrap them around a corner, or put them in an inside corner or a tight radius. You couldn’t put one in a valve seat area, for example, or in a combustion chamber between the cylinders — they take a lot of room and it has to be flat.
"Say you have a block with a big freeze crack on the side of it," Reed continues. "We used to put locks in to hold it all together and then stitch up the crack. Because when you torque the head bolts down, it lifts up on the crack. When the engine runs, you have thermal expansion of the cylinder walls and compression, lifting up on the crack. There’s a need to tie this metal back together. Not just seal it, but return structural integrity to the repair."
Cold Crack Repair 101
Unlike welding, which can take years to learn correctly, cold crack repair is relatively easy to learn and perfect for many applications, say rebuilders. If you have good mechanical skills and can drill a hole and tap it, you can do an adequate job. Still, it isn’t a procedure you would want a first-day employee to try alone.
"Pinning isn’t quite as easy as the manufacturers make it seem to be," says Tommy Begley, production manager with Groom’s Engines, Parts, Machining, Inc., Nashville, TN. "You still have to really pay attention to the details. There is some training involved — as well as some art. Common sense helps, too."
Recon’s Sterback echoes this. "It is fairly easy — but no, it’s not a ‘first-day’ process. Of course, we consider our people to have a fair amount of mechanical skills and common sense, and we take a lot of time with training. We feel very comfortable with the heads we pin."
According to Seal-Lock’s Diperstein, initial training on the basics of cold crack repair can be accomplished in just two to three days. "After that, it’s a matter of the manufacturer just answering installer questions about specifics as they come up."
This is a repair procedure that has a definite impact on shop profitability, according to Sterback. "We have five or six stations just for pinning. One head may take two or three labor hours while another may take just 15 minutes. Out of the 250 engines we rebuild each day, we probably pin 50 heads. We’re seeing more and more exotic cracks that require the use of a Lock-N-Stitch Castmaster plug, but at least 75% of the time we’re fixing surface cracks which allow us to use standard threaded plugs, which, in this case, make a more cost-effective repair."
The cost of pinning — low-cost materials, relatively little training expense and less labor time — makes this method of crack repair a highly profitable shop procedure. "You can see the profitability with pinning because you’re offsetting a higher cost repair," Sterback says.
But, will it last under today’s higher engine stresses? Each of the people contacted for this article gave an unequivocal "yes" to that question.
"We’ve done a certain amount of pinning virtually forever," says Groom’s Begley. "Each one gets pressure tested. We make sure they’re right before they leave — and we just don’t have them come back."
Diperstein says he knows of repairs that are still in place 40 years after being installed. And, Lock-N-Stitch’s Reed points out that the U.S. Army approved his product back in the 1980s.
"They dyno-tested 75 engines for 450 hours each, each with more than 20 repairs. They took some of the engines, froze them to -50° F, thawed them as quickly as possible and then ran them for 200 more hours," Reed says. "In fact, some of the vehicles in Desert Storm had been repaired this way."
As Excelsweld’s Geertsema points out, the war on cracks will likely be fought more and more often using cold crack repair methods almost by default. "The future for welding looks to be difficult — I just don’t see anyone who wants to be an up and coming welder anymore." It’s a good thing then, that metal stitching technology continues to improve.