Chain Tensioner Blues
TAKING AIM, by Chris Maida, Editor
I’ve been getting a lot of letters from readers concerned about the cam chain tensioners in their Twin Cam engines. They want to know at what mileage the fiber shoe on the tensioners will wear out. Unfortunately, there’s no simple answer to this question, since it depends on a few factors.
For starters, tensioner shoe wear is tied to engine rpm, not mileage. An engine spinning at 2500 rpm when the bike is in second gear and going 30 mph is wearing out its tensioner shoes the same amount as when the bike is in fifth and going 60, and yet the bike is traveling twice as many miles. This means a bike ridden mostly around town will wear out its tensioner shoes at a lower mileage than a bike ridden mostly on the highway.
Another factor to consider is whether your bike has the spring-loaded tensioners or the newer hydraulic units. The spring type is original equipment in all 1999-2006 Twin Cams, except 2006 Dynas, which got the hydraulic units that year. All 2007 to present Twin Cams have the hydraulic tensioners. This is important because the spring-loaded tensioners wear out much faster than their hydraulic counterparts. The spring-loaded tensioners are always applying the same amount of pressure onto the cam chain and, therefore, the tensioner shoes.
The hydraulic tensioners apply pressure based on engine oil pressure. When the engine is idling or at low power settings, engine oil pressure is low, so the tensioners are not applying much pressure to the chains, keeping shoe wear to a minimum. This is why the spring-loaded tensioners usually wear out their shoes in 15,000-30,000 miles while the hydraulic units have been lasting anywhere from 30,000 to 70,000.
You can check the outer tensioner’s shoe by pulling off the cam cover, which brings us to the final factor to remember. The inner tensioner shoe, on both spring and hydraulic tensioners, always wears out faster than the outer one. If the outer shoe is three quarters worn, the inner one is probably gone or just about to go.
To change the inner tensioner and its shoe, you have to pull the entire cam support plate assembly out of the engine and take this assembly apart. This is why many owners take this opportunity to upgrade to the new-style hydraulic units and cam support plate. (Why go into your engine again in 20,000 miles or so?) It’s also a good idea to upgrade to the new-style oil pump at this time. Many owners also put in a set of performance cams that don’t require any headwork at this time, since the only additional cost is the cams themselves, a fuel tuner, and the tuning time, but that’s a whole different issue.
See you on the road.
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This column originally appeared in issue #314 of American Iron Magazine.
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