Camshaft wear: symptoms and causes

A worn camshaft rarely shows dramatic symptoms - it creeps up on you. Power drops a little, the idle gets slightly rougher, and one day you are left with a lobe that barely lifts the valve. Understanding what wear looks like, what causes it and when it is time to act saves you from expensive secondary damage.

Visual signs of wear

The first thing you notice when inspecting the camshaft - or already on the lifters if you pull the valve covers - is the surface. Howard's Cams and Hot Rod Magazine describe several stages:

• Normal wear pattern - a cam lobe that has bedded in correctly with its lifter shows a narrow, even contact band (tracking pattern) that is centred but slightly offset from the middle of the lobe. That is normal and desirable.
• Pitting - small pits in the lobe surface, often at the flank. An early stage that can be tolerated briefly but signals that the surface is starting to give way.
• Scoring - deeper scratches along the surface of the lobe, usually caused by contaminated oil or a lifter that has stopped rotating. Serious - the lobe is damaged.
• Rounded nose - the tip of the lobe (the nose) has rounded off and lost lift. Clearly visible when compared with a new lobe of the same profile.
• Discolouration - a blued or brownish surface indicates extreme heat, often from insufficient lubrication or too much spring pressure.

The lifter reveals the problem

On a flat tappet lifter, the underside should be convex (crowned). If it is concave (dished) instead, the contact load has been too high - the lobe has hammered the lifter's face inward. That is a sure sign that both the lifter and the cam lobe need to be replaced.

Measurement: 0.025 mm matters

Visual inspection is not always enough. Measure the lobe's lift with a micrometer or feeler gauge and compare it against the cam manufacturer's specification. The rule of thumb from the engine-building world: 0.025 mm (0.001") of lost lobe lift shifts the valve timing events by around 3 crank degrees. That does not sound like much, but in a turbo engine a few degrees of timing deviation can noticeably affect boost buildup and overlap behaviour.

Check every lobe - wear is rarely spread evenly. A single worn lobe is enough to justify replacing or regrinding the whole camshaft.

Causes of cam wear

1. Insufficient ZDDP in the oil

ZDDP (zinc dialkyldithiophosphate) is the additive in engine oil that forms a protective sacrificial film at the metal contact between the cam lobe and the flat tappet lifter. Hot Rod Magazine points out that modern consumer oil (with the API starburst mark) has sharply reduced ZDDP levels because it can damage catalytic converters, but all modern engines run roller lifters that do not need ZDDP.

Older engines and performance builds with flat tappet need oil with at least 1,200-1,500 ppm zinc. Diesel oils ("big truck" oils) and specialist oils from performance oil manufacturers contain a sufficient level.

2. A failed break-in

The first 20 minutes with a new flat tappet cam are critical. If the break-in procedure is not followed - the right oil, the right rpm, the right spring pressure - the lobes can start to degrade before the engine even leaves the workshop.

3. Incorrect spring pressure

Kelford Cams stresses that flat tappet cams should never be run with a higher open pressure than the manufacturer's spec. Oversized springs load the lobe surface beyond what the sliding contact can withstand. On the other hand, springs that are too weak cause valve float, which slams the lifter back against the lobe uncontrollably.

4. Lifters that do not rotate

Howard's Cams explains that the flat tappet lifter's rotation in its bore is absolutely essential. The lobe's taper and the lifter's crown create the rotating motion. If the lifter sits too tight in the bore (under 0.03 mm clearance) or if the taper or crown is wrong, it will not rotate, and without rotation you get point loading that destroys the lobe quickly. A simple check: fit the cam, lifters and pushrods, press the pushrod down by hand and rotate the engine - the lifter should turn roughly one revolution for every revolution of the engine.

5. Contaminated oil or oil starvation

Dirt in the oil acts like grinding paste between the lobe and the lifter. Insufficient oil flow to the lifter bores - whether due to a clogged oil pump, blocked galleries or poor pump pressure - results in metal-to-metal contact with no lubricating film.

Regrinding vs replacement

A camshaft can be reground - that is the foundation of Meksta's camshaft grinding work. During a regrind, a new profile is ground onto the existing blank. It works as long as:

• The core material is not damaged deeper than what can be ground away
• The camshaft bearing journals are still within tolerance
• There is enough material left to hold the new profile's base circle, lift and transition radii

If a lobe is so worn that it lacks enough material, or if the cam shows cracks or deep discolouration, replacement is the only option.

Prevention

• Always use oil with the correct ZDDP level for flat tappet cams
• Follow the cam manufacturer's break-in instructions to the letter
• Match the spring pressure to the cam profile - no more, no less
• Inspect the lifters at every cylinder head job
• Check the valve lash regularly on mechanical cams - increasing lash can be the first sign

Summary

Camshaft wear is rarely sudden - it is progressive and diagnosable. Visual inspection, lobe measurement and attention to changes in valve lash catch problems early. The right oil, the right springs and a correct break-in prevent most of it. And if it is time regardless, contact Meksta and we will help you with a regrind or a new camshaft.

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