Maintenance Matters

May 2009 Issue

The Cam Problem: Corrosion, Failures

Shops are telling us both Lycoming and Continental cams show more premature failures and getting a second run out of one is iffier than it used to be.

Just as you thought it was finally safe to buy a cylinder, now comes a crisis over camshafts. Specifically, engine shops tell us they’re seeing premature wear and failures due to spalling and many also report that cams that used to make it through one TBO run and into another are now too worn to reuse. This trend has actually been brewing for a number of years and no one seems able to say definitively if it’s getting better or worse. Opinions bridge the divide. "Definitely worse, in my opinion," says Penn Yan Aero’s Bill Middlebrook, who shipped us a couple of scrapped cams to prove the point, along with a couple of spalled lifters. "We had a brand new cam come apart in the test cell—it wiped one lobe," he added. This sort of thing used to be limited to Lycomings, whose cam is mounted higher in the engine core, away from oil misting from the crankcase and in line with blowby from the cylinders. But lately, shops tell us they’re seeing more cam-related wear issues in Continental engines, too. TCM seems to have noticed this and in 2005, it issued SID 05-1, a service directive related to cam and tappet wear. And speaking of tappets, some in the industry think that’s definitely the problem and a worn cam is the secondary result. "We think the problems definitely start in the lifters, predominantly," says Greg Merrill at Aircraft Specialties Services, a Tulsa house that regrinds and reconditions cams and tappets for many engine shops. His company also developed CamGuard, an anti-wear, anti-corrosion oil additive. "We do see the occasional cam with a bad lobe, but it’s rare. It’s almost always a problem with the tappets," Merrill adds. What exactly is going on here? Everyone has a theory, so take your pick. Some, like Allen Weiss at Opa Locka, Florida’s Certified Engines believe that something changed in the fuel or the oil in the recent past, recent being perhaps in the last 10 years.

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