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Era Of Aluminum: Late-Model OHC Head Rebuilds
By Brendan Baker
Over the last few years, manufacturers have abandoned cast iron heads in passenger cars and light trucks. Cast iron is heavy and the more radical, lighter, aluminum overhead cam (OHC) designs are the challenges and opportunities facing today’s engine builders. Aluminum offers many advantages, but the cost to manufacture them is still relatively high. New aluminum castings are appearing for certain applications. But for most applications, aluminum cores remain the starting point for head rebuilds.
Most of the cylinder head rebuilders we talked to said that they repair from 70-90 percent of their cores. Rebuilders say an even higher percentage could be rebuilt, but that it just isn’t cost effective to do so in light of a new casting or a better replacement core.
Core availability for late model heads doesn’t seem to be a big issue. Most rebuilders say that is because new castings have in many cases filled in where cores were once unavailable or unrebuildable, and also better rebuilding techniques have made cores that were once thought to be junk, now repairable.
It’s possible for an engine shop to specialize in late model head work and carve out a nice niche in their area. More likely, however, engine builders will choose to supplement their other services and fill in gaps with these types of jobs.
A major advantage to doing head work is that turnaround times are quick and therefore can help generate cash flow in a tough market. One rebuilder we spoke with said that whenever he has an opportunity to turn a job into cash in one or two days, it becomes his top priority.
Lee Menke, owner of R&R Machine located in Akron, OH, says that the key to keeping these types of jobs in his shop is quick turnaround times. R & R Machine offers 1-3 day service depending on the head.
R&R Machine is a prime example of a full service shop. It mainly specializes in heavy-duty industrial engines, but offers a full array of auto and truck rebuilding service. R & R is a fairly large rebuilder and has a lot invested in the latest equipment. From locomotive heads to late model OHC aluminum cylinder heads, R & R can handle most rebuilding applications.
Menke says that what is most in demand today in the aluminum OHC market is the multi-valve, 4-cylinder and V6 heads. Menke stocks the most popular heads allowing R & R quick turnaround times and positive cash flow. Much of what Menke has invested in equipment can be used on a wide variety of engines. His cleaning equipment, for example, can be used for just about all the jobs he does, even some of the mammoth heavy-duty diesels.
Doug Anderson, president, Groom’s Engines, Nashville, TN, points out that the biggest obstacle in rebuilding late model cylinder heads is the cleaning process. "Whether you use soda, pressure wash them, or dry clean them, it’s not easy. You must make sure you get them completely clean and that you don’t leave anything behind."
Anderson cites the example of glass beads – you had better make sure you get all the glass bead out of the passages in the head or you could be facing a potential warranty claim.
Opinions vary on the best approach to cleaning late model aluminum heads. We talked to many engine builders that use ovens, blasting media, spray washers and aqueous systems, all of whom claim success. The best advice is to know the proper techniques to employ when using each type of cleaning equipment.
Many rebuilders use some sort of oven to clean their heads, according to Richard Moore, owner, Auto Motive Machine in Miami, FL. Moore’s shop does about 200 heads a month, mostly import aluminum heads. However, Moore says his shop "uses our ovens less frequently now because we know heat is really not good for (many) of these late-model aluminum heads.
"I’ve talked to some shops around the country that say they don’t put anything in an oven because temperatures over 500° F cause aluminum heads to lose their strength. But you have to take it up to about that temperature to get it clean." Although Moore says his shop has been heat cleaning heads for some time, he says he feels with newer, late model aluminum heads you can avoid some problems, like stripped threads for example, by not using heat cleaning. "Cleaning the head properly is one of the biggest, most expensive aspects of the whole rebuilding process," admits Moore.
Cleaning is one aspect of the rebuilding process, but you have to tear it down first. The extent of this depends on how much of the engine you’re rebuilding. In most cases, tearing down late model aluminum OHC heads is much more difficult and time consuming compared to cast iron. "You’ve got to be careful when taking these OHC heads apart. The valves are way down in a hole in many cases, so it’s hard to get them out without damaging the lifter bore," notes Groom’s Anderson.
Disassembling these heads can require special tools and equipment. If you’re doing a large volume of heads, a cylinder head workstation may do just the trick. These machines can take the headache out of assembly/disassembly, and it makes rebuilding quicker and easier. One manufacturer says using a workstation can save one hour of labor per head, which in a year’s time doing 100 heads a month can add up to approximately $2,000 in savings. Many of these machines come with rotating tables, quick clamping devices and high-powered pneumatic cylinders to compress valve springs and remove or install keepers.
After you get the heads torn down and thoroughly cleaned comes the next phase – you have to get them straight. There are several different ways to straighten aluminum cylinder heads and everyone has their own way of doing it. Some shops put them on a steel plate and put them in an oven; some press them; and some heat them.
Once they’re apart and clean, you have to deal with stripped threads, and because you’re dealing with aluminum you usually have some damage to the head. Spark plug holes often require thread inserts. According to Groom’s Anderson, spark plug thread repair is a common problem with aluminum heads.
Cam bore damage is another typical problem with aluminum OHC heads. Many OHC heads require line boring and some require the use of oversize cams if they’re available. Most late-model OHC engines don’t have cam bearing inserts. The camshafts ride directly on the aluminum surface with the only lubrication being a thin film of oil between the cam journal and head. And when the oil viscosity breaks down, guess what happens? Cam seizure is commonly the result. Overheating can also cause cam bore damage. Usually the middle bores are the most damaged because the head bows up in the middle.
The valves are small on late-model multi-valve OHC heads so concentricity is also an issue. "A little bit of runout on an itty-bitty valve is a lot. You also have valves and springs to deal with and 24 lifters can get really expensive, too. If you have a Chrysler 3.5L, you can’t buy the lash adjuster – you have to buy the whole rocker. A set of rockers with the lifters will cost you about $500! Needless to say, some rebuilders have figured out ways around that, but it’s not easy," says Anderson.
It takes a lot longer to rebuild an aluminum OHC head than it took with cast iron OHV heads. "If you spent more than 30 or 40 minutes on everything from start to finish, you were wasting time somewhere," says Anderson. Today we have aluminum heads that take 2 to 2-1/2 hours to rebuild plus another hour to repair. Then you have to build up the rocker shaft assemblies. Some, like the Saturns, have needle bearings that tear up the shafts and the rockers – and they’re not cheap. Saturn gets $45 a piece for the shafts and there are two of them on the SOHC head. Cams for these engines are expensive, too. You can easily spend $150 to $200 on a cam for a 1.9L Saturn or a 4.6L Ford."
Chuck Tiller, co-owner of Aluminum Head Rebuilders (AHR) in Portland, OR, says that he and his partner, Wayne Sullivan, have been in the automotive business for about 30 years each. "We’ve done a little bit of everything in the automotive industry," he says. "We chose to get into late-model cylinder head rebuilding primarily because it’s very specialized, and we felt that to be successful in this business you have to have a niche."
AHR has been in business since 1995. In that time Tiller has seen his production mix change from doing a majority of import head work to about an equal amount of domestic and import head work today. "When we first started we did about 70% to 80% import work," says Tiller. "It’s more like 50% import, 50% domestic now, and I think by the end of the year it’ll be closer to 60% domestic and 40% import."
In the last few years domestic manufacturers have gone to aluminum OHC heads. "They’re all going through a learning curve, like the Japanese did, so the quality isn’t always there yet," says Tiller. AHR is seeing a significant amount of failures on the domestic side. The domestic manufacturers’ problems are similar to what the Japanese manufacturers went through when they switched to aluminum heads about 20 years ago. "The biggest thing we’re seeing is the poor quality of the castings," says Tiller. "For instance, all the late model GM stuff looks like Styrofoam, and many of them have developed cracks that need repair. Although he says, unless there was a "catastrophic failure" about half of the Saturns and almost all of the GM heads have been repairable.
AHR still does a lot of import work because of its location. Portland and the Pacific Northwest, in general, is a big import market. "We have a lot of Volvos and BMWs in the area," Tiller says. "For a while BMW was putting out a really good product – almost no problems. But now the late-model twin cam they went to in 1993 is starting to crack like their old ones did.
"Literally, all the new twin-cam (BMW) heads are developing cracks. We don’t know at this point if it’s a design problem or a problem with the casting, but it doesn’t appear to be a cooling system failure. It’s similar to the BMW heads from the late ’70s and early ’80s. In the late ’80s and early ’90s BMW was running engine temperatures around 210° F and that caused many of their aluminum heads to fail. I’ve noticed now, since about ’94-’95, they lowered the cylinder temperatures back down by using a swirl type combustion, which while lowering the engine temperature still gives good fuel economy. As a result there have not been nearly as many problems," he says, adding that other manufacturers have done this as well.
Core availability, says Tiller, is not as big of an issue as it once was either. A few years ago, certain cores were hard to find, but the ability to find cores on the Internet has changed things a bit. Tiller says he now buys most of his cores on the Internet. Matching supply with demand may sound more like a FedEx commercial than a core issue, but that has been the effect of the Internet.
According to Tiller, there are several core suppliers in the area, thanks in part to an engine builder in Spokane that has built a healthy market in the Northwest.
AHR sells all of its heads exchange. "We guarantee all of our heads with at least half value core exchange. That way if the core isn’t good the customer still gets something back," says Tiller. "We see a large percentage of cores that aren’t repairable – probably only 30 percent of them are good enough to repair. And most of the time that is why they are buying a rebuilt head anyway – because it’s not cost effective for them to repair."
The cost of equipment can be a barrier to some shops wanting to do late-model head work, too, but there are ways to customize the tooling you may already have. AHR makes all of its own plates for pressure testing on a universal pressure tester. "We have found that universal pressure testing machines can’t apply the kind of pressure we really need," explains Tiller.
"We have made our own plates for each application as we go along. We usually make about two plates a month. This way we can plate a head to 120 psi, and it’s much more effective at finding leaks. In some instances, we’ll plate it up and bake it in the oven at 250° F. It’s a lot more accurate for depicting running conditions and may help find a small leak that might otherwise be hard to find."
But, some rebuilders have found one of the reasons they get late-model head work is because they’ve invested in the latest tooling. "I seem to never make any money because I am always purchasing new equipment I need to do a better job," says Auto Motive Machine’s Richard Moore. "I didn’t go out asking for late-model work, it just happened, and the reason it did is because we try to tool up for what’s necessary."
According to Moore there are three things that have made a significant difference in his 22 years of business. "Learning how to weld has probably made the biggest difference," he claims. "Giving a one-year guarantee made another big difference. Also, being able to straighten and line bore has made a difference, too."
Welding is a critical component to late-model cylinder head repair and the value cannot be overlooked. Moore says that he took a welding course several years ago and learned the basics, but what made him into a good welder was practice. "We don’t send much out at all," he says. "My competitor down the street doesn’t weld so he buys new cast heads. I have offered to fix his cores for him, but for some reason he doesn’t want to give me business. He scraps cores that could be repaired, and sells new aftermarket heads instead. However, my heads are usually cheaper than his new heads."
While there are probably some areas of the country where core availability is an issue, for the most part they are readily available either over the Internet or from core suppliers and salvage yards. But, depending on your equipment and personnel it may be more cost effective to buy new cast heads or rebuilt heads from a cylinder head supplier or remanufacturer.
Import heads still hold a larger percentage of the late-model OHC market. But domestic aluminum OHC heads are becoming more common. And the domestic manufacturers’ learning curve will benefit late-model cylinder head rebuilders.