The main bearings of an engine aren’t the sexiest things to talk about when you are discussing building a performance powerplant. For most of us, engine bearings are something we slap in, ensure the fit is right, have enough clearance, and then pretty much forget about them. When an engine bearing is working like it’s supposed to, then it isn’t something you really have to concern yourself with. Now, when an engine bearing fails, well, that is bad for everybody, and usually results in a lot of oil cleanup. When constructing an engine with a lot of horsepower, bearing choice becomes more critical. To find out why, we talked with the folks at MAHLE who design and manufacture high-end engine bearings every day.
MAHLE started out as a piston company back in the day (and they do still make pistons), but these days, the company is mainly known for its engine bearings. Most notably, the MAHLE team manufacture the Clevite engine bearings used by both NHRA and NASCAR teams, among others. We sat down and chatted with Dan Begle, Performance Sales Engineer at MAHLE Aftermarket, and he laid out for us why bearing choice in racing engines is so important. The first thing you need to know about Begle is he is a definitive expert on engines. He has 27 seasons under his belt working at NASCAR engine shops. He had his own shop for while and also did 13 years working for Robert Yates Racing Engines. His job at Robert Yates was as a reliability specialist performing failure analysis on all of the team’s race engines.
As the person who figures out why engines fail, Begle wasn’t always popular with the NASCAR drivers. Joey Lagano came through Robert Yates’ shop and when he met Dan he said, “So, you’re the guy that raises the flag when my parts don’t look good and I’m to blame for hurting these engines.” Begle’s reply was a simple, “Yup, I’m that guy.” Begle says he can look at parts and immediately know which car they came out of.
“For example Carl Edwards versus Greg Biffle,” says Begle, “Their engines had completely different component colors.” Historically, racecar drivers never like to take the blame for anything that happens. Drivers will say, “I didn’t do anything.” But, a quick look at telemetry will show they shifted from third to second instead of third to fourth. But sometimes it isn’t a missed shift that causes havoc. “Wheel hop on road courses can cause the engine to unload which causes an over-rev. We will see that evidence when tearing down the engine,” Begle says.
Now that Begle has moved on from working specifically with NASCAR teams and is full-time at MAHLE, he has the opportunity to be involved in the improvements of engine component manufacture and be innovative. “People send me pictures of rings and bearings, and I can help mentor people, whether you are a newbie to motorsports or a seasoned veteran,” says Begle. “At MAHLE I get to help find solutions to engine problems for a lot of people.”
According to Begle, he simply enjoys geeking out as an engine builder. “I have put in thousands of bearings. It is a part you don’t really think about. They stick them in and go. I know because I was there. Bearings are kind of like gaskets. People have no clue what goes into a bearing or a gasket, they just bolt it on and go. But, there is so much technology in these components.”
Some of the technology and design that Begle is referring to is what MAHLE puts into its Clevite bearings. “Clevite is our Tri-Metal bearing with a steel back, and a cast copper-lead substrate with an overlay. The term Clevite is known in the industry for cast-copper lead, it is different than other manufacturers. Cast-copper lead is created by melting materials and then cooling them, putting in a strength grain, and then molting it at 2,000 degrees, which makes the bearing 20- to 30-percent stronger. It is so strong, it can handle 11,000 horsepower. Anytime you see that kind of horsepower, that is a Clevite bearing.”
Currently, Begle takes care of MAHLE’s NHRA nitro top fuel customers. “Those NHRA teams use new bearings after every quarter-mile run. They use how much the rod bearing compresses to let them know how much more tuneup they can put into the car. They measure the bearing when it goes in and when it comes out, and that measurement helps them know how far they can go.”
Clevite bearings are commonly used in aluminum engines. Believe it or not, aluminum engines can require a different bearing than a cast-iron engine. “There are certain applications, for instance, a big-block Chevy aluminum block where Clevite can really make a difference,” says Begle.
Aluminum’s Growing Pains
“When a block manufacturer converts from a cast-iron block to an aluminum block, we will use a different bearing. Take the big-block Chevy, for example. It was originally cast iron, but in racing weight is speed, so aluminum is lighter and therefore quicker. But aluminum has more thermal growth. We design a bearing based on a housing bore. There is a dimension called stand-off: one bearing is flush, the other stands proud; the amount is stand-off. When they are clamped together a force is applied. We call that clamp load, which gives us contact pressure for the bearing.”
With more thermal growth in the main housings, the main bearings want to walk around inside the main bore. Begle did analysis on this and used a lot of engineering to determine there was not enough clamp load on the bearing when the block was at operating temperature. The thermal growth was too much with an aluminum block and the bearing would move or spin.
Begle’s team attempted to get more oil clearance in an aluminum block by making the housing bore larger, but that reduced the clamping force, making the problem even bigger. They got oil clearance, but they lost force to keep the bearing in the block. Begle says, “We figured out what we needed to do for thermal movement of an aluminum block. We determined exactly how much stand-off needs to be in place. MAHLE has a database all bearings go through to get this just right.”
For bearings to handle the thermal change in an aluminum block, it all comes down to stand-off when installing the bearings. “We use some bearing stand-off on all of our aluminum blocks, big-block Chevy, and Hemi blocks in the Nitro world,” said Dan. “Any race Hemi will have stand-off for that aluminum thermal growth.”
Currently, NHRA racers are mandated to run the Hemi main bearing. Begle indicated in racing applications things really get dicey. Crank torsion can cause bearings to walk. He can see wear on the overlay, showing crank whip happening. One of Begle’s creedos is that all parts have a story to tell. You just have to know what to look for. From that data, you can diagnose and build better engines.
Clevite engine bearings have been tested and given a 12,000 psi rating, the highest in the industry. They are more resistant to corrosion and out-perform traditional bearings by a claimed 20-percent or more, making Clevite’s TriMetal material the strongest currently available in the industry. We also spoke with another employee at MAHLE, Bill McKnight. McKnight is the training team leader and he is the actual person who answers all of the online tech questions that come into MAHLE.
McKnight says, “Anything above 400 horsepower you need to be looking at race bearings.” He explained how a passenger car can have a very hard bearing that can last for 250,000 miles. However, a racing engine needs a completely different type of bearing — a softer bearing that can handle the loads of high horsepower. These bearings will allow for more horsepower but, will also need to be replaced sooner than that of your average grocery-getter.
MAHLE makes several different styles of race bearings. The H-Series (copper-tin-lead TriMetal bearing) is a harder bearing with less flex. The K-Series is moly-based and works at high temperatures. The V-Series (lead indium overlay) has the same bearing strip, with different plating. It’s softer, so it won’t last as long, but allows for movement of parts when you make a lot of horsepower. Then the M-series is designed for extremely special applications where increased crank deflection load the edges of the bearings.
While the reality is an all-out race bearing is not going to get 100,000 miles of service life, but it will handle huge horsepower demands. When getting into high-power aluminum applications, there are so many more variables to consider. Luckily, Clevite has done most of the homework already.