The Summit Racing tech department tackles your automotive-related conundrums. This week, we’re discussing common causes of camshaft failure and what you can do to prevent it. 

Q: What causes a camshaft to fail?

A: We’ve gotten that question (or something very similar) a lot. We’ve also heard a lot of questions about camshaft installation and break-in procedure. Since proper installation and break-in go hand-in-hand with camshaft success or failure, we’ve decided to tackle it all in one post. In conjunction with the Summit Racing tech department, we’ve assembled the eight most common causes of camshaft failure:

1. Lobe wear

Lobe wear is often caused by improper lubrication during installation.

Use only the manufacturer recommended lubricant, which is generally included with the cam. This lubricant must be applied to every cam lobe surface, and to the bottom of every lifter face of all flat tappet cams. Roller tappet cams only require engine oil to be applied to the lifters and cam.

Also, apply the lubricant to the distributor drive gears on the cam and distributor.

2. Improper Break-In

After the correct break-in lubricant is applied to the cam and lifters, fill the crankcase with fresh, non-synthetic oil. Use motor oil with an engine break-in additive (ZDDP or ZINC camshaft additive), especially with flat tappet camshafts.

Prime the oil system with a priming tool and an electric drill so that all oil passages and the oil filter are full. Preset the ignition timing and prime the fuel system. Fill the cooling system. Start the engine, run it between 1,500 and 3,000 rpm, varying the rpm up and down in this range for 20 minutes. During break-in, verify that the pushrods are rotating, as this will show that the lifters are also rotating. If the lifters don’t rotate, the cam lobe and lifter will fail. Sometimes you may need to help spin the pushrod to start the rotation process.

3. Old Lifters with a New Cam

You can use new lifters on a good used cam, but never pair used lifters with a new cam.

If you are removing a good used flat tappet cam and lifters and are planning to use them again in the same (or another) engine, you must keep the lifters in the order they were removed from the cam they were on. Lifters “mate” to their specific lobes and can’t be changed. If the used lifters get mixed up, discard them, install a new set of lifters, and break in the cam again.

4. Incorrect Valve Spring Pressure

Never install valve springs without verifying the correct assembled height and pressures. Recommended valve spring pressures are as follows:

  • Street-type flat tappet cams: 85-105 pounds
  • Radical street flat tappet cams: 105-130 pounds
  • Street-type hydraulic roller cams: 105-140 pounds
  • Mechanical street roller cams: no more than 150 pounds

Race roller cams with high valve lift and spring pressure are not recommended for street use, because of a lack of oil splash onto the cam at low speed running. Springs must be assembled to the manufacturer’s recommended height.

5. Mechanical Interference

This comes in a few different forms:

  • Spring coil bind: This happens when all the coils of a spring contact each other before the valve fully lifts. Valve springs should be capable of traveling at least .060 inches more than the valve lift of the cam from its assembled height.
  • Retainer to seal/valve guide boss interference: At least .060 inches of clearance is required between the bottom of the retainer and the seal or the top of the valve guide when the valve is at full lift.
  • Valve to piston interference. This occurs when a change in cam specs (lift, duration, or centerline) is enough to cause the valve and piston to contact. Also, increased valve size or surfacing the block and/or cylinder head may cause this problem. Minimum recommended clearances are .080-inch intake and .100-inch exhaust.
  • Rocker arm slot to stud interference. As you increase valve lift, the rocker arm swings farther on its axis. Therefore, the slot in the bottom of the rocker arm may run out of travel and the end of the slot will contact the stud and stop movement. The slot in the rocker arm must be able to travel at least .060-inch more than the full lift of the valve.

6. Excessive End Play

Some engines use a thrust plate to control the forward and backward movement of the camshaft in the block. The recommended amount of end play on these types of engines is between .003- to .008-inches. Many factors can cause end play to change. When installing a new cam, timing gears, or thrust plates, be sure to verify end play after the cam bolts are torqued to factory specs. If the end play is excessive, it will cause the cam to move back in the block, causing the side of the lobe to contact an adjacent lifter.

7. Broken Dowel Pins or Keys

The dowel pin or Woodruff key does not drive the cam; the torque of the timing gear bolts against the front of the cam does. Reasons for the dowel pin or key failing are: Bolts not being torqued to correct specs, incorrect bolts of a lower grade stretching and losing torque, not using the correct hardened washer which may distort and cause torque of the bolt to change, LocTite not being used, or some interference with the cam, lifters, or connecting rods causing the cam to stop rotation.

8. Broken Cam

A broken camshaft is usually caused by a connecting rod or other rotating part coming loose and striking it. Sometimes the cam will break after a short time of use because of a crack or fracture in the cam due to rough handling during shipping or improper handling prior to installation.

Keywords
Camshafts, Monday mailbag
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Author: OnAllCylinders Staff