Camshafts: To replace or not to replace

Blogs Truck Parts and Service Staff July 2, 2013

So, you have 1,000,000-plus miles on your engine and you’ve decided it’s time for a rebuild. Some parts you know you have to replace but others you aren’t so sure about. Fuel injectors, oil coolers, oil pumps, and oh, what about the harmonic damper? Our staff gets questions on these parts all the time, but one item that doesn’t get nearly as much attention is the camshaft, and it should.

A high mileage camshaft needs to receive just as much care as any other “standard” replaceable part during the rebuild process, but it is often overlooked. Most people assume that if the camshaft isn’t flaking, pitted or ground right down, it can be put back into use without any further inspection or maintenance.

However, in many instances a camshaft can be worn well past its reuse limit without any obvious visual signs of wear and tear. The old, “I ran my fingernail across it and it didn’t snag” routine just doesn’t cut it anymore.

So what’s changed with camshafts?

The need for more horsepower, better fuel economy and lower emissions has led to the demand for improved cam designs. A great example of this can be seen in racing. NASCAR is very closely regulated to make sure every team is using the same engine.

The basics of the engine haven’t changed in years, yet the horsepower being produced from these engines has increased from 650hp to as much as 900hp. Most of this boost can be attributed to more aggressive cam lob profiles but because they place added stress on valve train components, they also need to be replaced with more sophisticated parts. Diesel engine manufacturers are using the same principles to drive advancements.

How does this affect your engine rebuild?

Almost all newly manufactured engines feature camshafts with lobe designs that make it difficult for the average repair shop to measure wear and tear. In most instances the repair shop will only send the cam and cam followers to the machine shop for repair if they see visual signs of damage.

The assumption should be made that any wear on the cam will also be found on followers, so they should also be sent out. Makes sense, right?  Wrong.

Many repair shops lack the training and tooling to handle new camshafts. The tooling required at a machine shop to measure, let alone repair these new camshafts is extremely expensive. It can easily cost over $100,000 for the measuring stand and a CNC machine capable of repairing a cam can go into the millions. For these reasons 90 percent of machine shops are unable to properly repair the latest camshafts.

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