A worn camshaft rarely announces itself with dramatic symptoms. It creeps up on you. Power drops a little, the idle gets slightly rougher, and one day you are looking at a lobe that barely lifts the valve. Understanding what wear looks like, what causes it and when to act saves you from expensive follow-on damage.
Visual signs of wear
The first thing you see when inspecting the camshaft, or already on the lifters once the valve covers come off, is the surface. Howard's Cams and Hot Rod Magazine describe several stages:
- Normal wear pattern: a cam lobe that has broken in correctly with its lifter shows a narrow, even contact band (tracking pattern), centered but slightly offset from the middle of the lobe. That is normal and desirable.
- Pitting: small craters in the lobe surface, often on the flank. An early stage that can be tolerated briefly, but it signals that the surface is starting to give way.
- Scoring: deeper grooves along the lobe surface, usually caused by contaminated oil or a lifter that has stopped rotating. Serious. The lobe is damaged.
- Rounded nose: the tip (nose) of the lobe has rounded off and lost lift. Clearly visible next to a new lobe of the same profile.
- Discoloration: a blued or brownish surface indicates extreme heat, often from insufficient lubrication or excessive spring pressure.
The lifter tells the story
On a flat tappet lifter, the underside should be convex (crowned). If it is concave (dished) instead, the contact load has been too high and the lobe has hammered the lifter face inward. That is a sure sign both lifter and cam lobe need replacing.
Measurement: 0.025 mm matters
Visual inspection is not always enough. Measure the lobe lift with a micrometer or feeler gauge and compare 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 roughly 3 crank degrees. That sounds like nothing, but in a turbo engine a few degrees of timing drift can noticeably affect boost build-up and overlap behavior.
Check every lobe. Wear is rarely evenly distributed, and 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 on the metal contact between cam lobe and flat tappet lifter. Hot Rod Magazine stresses that modern consumer oil (carrying the API starburst label) has sharply reduced ZDDP content, because ZDDP can damage catalytic converters, and every modern engine runs roller lifters that do not need it.
Older engines and performance builds with flat tappets need oil with at least 1,200 to 1,500 ppm zinc. Diesel oils ("big truck" oils) and specialty oils from performance oil brands contain sufficient levels.
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 (right oil, right rpm, right spring pressure), the lobes can start degrading before the engine even leaves the shop.
3. Wrong spring pressure
Kelford Cams stresses that flat tappet cams should never be run with more open pressure than the manufacturer's spec. Oversized springs load the lobe surface beyond what the sliding contact can handle. On the other hand, springs that are too weak cause valve float, which slams the lifter back against the lobe uncontrolled.
4. A lifter that does 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 its bore (under 0.03 mm clearance), or if the taper or crown is off, it stops rotating, and without rotation you get point loading that destroys the lobe fast. A simple check: install the cam, lifters and pushrods, press down on the pushrod by hand and turn the engine over. The lifter should rotate roughly one turn per engine revolution.
5. Contaminated oil or oil starvation
Dirt in the oil works like lapping compound between lobe and lifter. Poor oil flow to the lifter bores, whether from a clogged oil pump, blocked galleries or low pump pressure, means metal contact with no oil film.
Regrinding vs replacement
A camshaft can be reground. That is the foundation of Meksta's camshaft grinding work. A regrind puts a new profile on the existing core. It works as long as:
- The core material is not damaged deeper than what can be ground away
- The cam bearing journals are still within tolerance
- There is enough material left to support the new profile's base circle, lift and transition radii
If the lobe is so worn that the material is no longer there, or if the cam shows cracks or deep discoloration, replacement is the only option.
Prevention
- Always use oil with the right ZDDP content for flat tappet cams
- Follow the cam manufacturer's break-in instructions to the letter
- Match spring pressure to the cam profile, no more and no less
- Inspect the lifters at every cylinder head job
- Check the valve lash regularly on mechanical cams. Increasing lash can be the first warning sign
The short version
Cam wear is rarely sudden. It is progressive, and it can be diagnosed. Visual inspection, lobe measurement and attention to changes in valve lash catch problems early, while the right oil, the right springs and a correct break-in prevent most of it. And if the time has come anyway, contact Meksta and we will help you with a regrind or a new camshaft.