Nothing lasts forever, and engine parts are no exception. Well maintained engines should last upwards of 200,000 miles, but sometimes they don’t because of internal parts failure. Here is a list of some common causes of these failures:
Most common causes of bearing failure usually consists of dirt contamination, loss of lubrication (low or no oil pressure), oil break-down (not changing the oil in a timely manner). Bearings can also fail at high mileage due to metal fatigue. Bearings can also become pitted as a result of corrosion, also due to not changing the oil often enough.
Worn piston rings can lead to oil consumption, oil burning, loss of compression and loss of power. Piston ring wear can also be caused by dirt contamination, loss of lubrication (low or no oil pressure), oil break-down (not changing the oil in a timely manner), and may break as a result of detonation (spark knock).
Pistons that are “Burned” (a hole melted in a piston) is usually the result of detonation (spark knock) and pre-ignition which are commonly caused by an overly lean fuel mixture. Underlying causes include dirty fuel injectors, improper air/fuel mixture, over advanced timing, low octane fuel.
Rods can sometimes break or snap as a result of excessive RPMs or bearing seizure. Stock powder metal rods in late-model engines often need to be upgraded to forged steel rods if significant power modifications are being made!
Bearing seizure, loss of oil pressure, rod failure, main bore misalignment, missing or out-of-balance harmonic balancer, or excessive loads on the crank snout can cause catastrophic failure. Crank journals with minor damage can be reground to an undersize and fitted with an oversize bearing equivalent to the offset.
Excessive overheating of the engine, stretching or fatigue, loss of valve-lash or detonation/pre-ignition can cause failure in exhaust valves. High-mileage exhaust valves shouldn’t be reused, replace with new.
On Interference engines intake valves may be bent if a timing belt or chain breaks, allowing the piston to contact the valve. Of course a bent valve must be replaced! Carbon build up on the valves can also be a problem if the valve guides are worn or if the engine has GDI (Gasoline Direct Injection). These carbon covered valves will obstruct airflow and cause performance issues.
Springs typically lose tension over time due to metal creep, or they may actually break due to metal fatigue. New springs are definitely recommended for high-mileage engines.
Guide wear can be caused by normal side loading from the valve stem. Wear will increase oil consumption and may foul the intake valve with carbon build up. Guides may be replaced, reamed to new valves with oversized stems or even restored.
CAMSHAFT & LIFTERS
Poor lubrication is the ultimate cause of failure in this section! Oil that lacks sufficient anti-wear additive (ZDDP) may contribute to an accelerated wear. ZDDP (Zinc dialkyldithiophosphates) additive or specially formulated oils that are recommended for older flat tappet engines can prevent such wear. A new camshaft should never be used with old lifters.
Excessive RPMs and overloading may bend the pushrods causing cylinder misfire and valvetrain noise. Stronger, stiffer pushrods are recommended for all performance applications.
Believe it or not, chains stretch with age, which eventually leads to noise and change in valve timing. A stronger double-roller chain is recommended for all performance applications.
These are used on engines with VVT (Variable-Valve Timing). Phasers may become noisy as a result of high-mileage wear or failure due to becoming clogged with sludge.