Auto Repair Q&A



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Camshaft Repair

Overhead cam

The camshaft, one of the most important mechanical components of an engine. It consists of a thick steel rod onto which cams (egg-shaped bumps) are either milled or attached. Most modern vehicles have overhead cams, making them relatively easy to get to for the DIY mechanic.

The bad news is that when a camshaft goes bad, which is rare, it is likely due to a much more serious engine problem.

How a Camshaft Works

The camshaft is usually turned by a pulley around which the timing chain or belt pulls. As the engine turns, the crankshaft in the block turns the belt, which then turns the camshaft(s). Most engines have overhead camshafts, either one down the middle or one on either side, sitting on top of the heads.

The camshaft itself turns inside its bearings and each cam pushes down on a cylinder at just the right time. This creates or relieves pressure inside the cylinder, depending on the engine design or timing setup.

Camshafts are lubricated by engine oil.

Most Common Camshaft Failures

The most common reasons for a camshaft repair or replacement are:

  • Bearing Wear-Out
  • Sliding Friction Damage
  • Structural imperfections

The last reason is rare, as most auto manufacturers thoroughly test the robustness of their camshafts before selling a car. If this is the reason the camshaft has failed, it will likely happen early in the car's life rather than later.

Bearing replacement

The first reason, bearings wearing out, is the most common camshaft issue. The engine will make loud knocking or squeaking noises while running and listening closely will pinpoint the problem as being in one of the camshafts. Replacement of the bearings is required.

If a bad bearing is left for too long, then eventually the second failure will happen as the failed bearing will allow the camshaft itself to wiggle or slide while it's turning. This leads to serious wear on the camshaft and likely wear on everything attached to it.

Common Camshaft Repair Issues

When the camshaft fails, the issue is usually not with the camshaft or its bearings, but with something else in the engine. Most often, this is due to not having adequate lubricant.

Inadequate lubrication comes from not changing the engine oil often enough or using the wrong type of oil for the vehicle's needs.

Other common failure reasons can be distributor linkage problems, a bad timing belt, loose pulleys, and similar problems.

Camshaft repair can be an expensive process, but not necessarily time consuming. A qualified, experienced mechanic will require from 1 to 4 hours to do this, depending on whether the seals need replacement (new camshaft usually means new seals as well). The cost of the camshaft itself varies by vehicle, but most average in the $350 range for new ones. Older ones can sometimes be turned on a lathe to restore them, but only rarely.