Valvetrain & Camshaft

That pattern points strongly at valve stem seals. While the engine sits, oil drains down the valve guides and collects on top of the valves, then burns off in the first few seconds of running, which is why the smoke appears at start up or after idling at a junction and then clears. Worn rings smoke more consistently, especially under load, and come with crankcase pressure and reduced compression. A compression and leakdown test separates the two before you commit to a repair.

On many engines yes, and it is a worthwhile job. With the camshaft removed and the piston at top dead centre, compressed air is fed into the cylinder through the plug or injector hole to hold the valve up while the spring is compressed and the keepers removed. The seal is then changed and everything reassembled. The risk is dropping a valve into the cylinder if air pressure is lost, which means the head has to come off after all. Work methodically and keep the pressure on.

Because the seal cannot compensate for a worn guide. If the stem can rock in its guide, the valve wobbles as it opens and the seal is worked sideways on every cycle, so oil finds its way past regardless of how new the seal is. Measure guide clearance before deciding: where it is within specification, seals alone cure the smoke, and where it is not, the head needs guides replaced or reamed, which means removing it.

Excessive valve clearance in most cases, which on engines with shim or mechanical follower adjustment means the clearance has opened up as the valve seat wears in. On engines with hydraulic followers, tapping usually means a follower that has bled down, which is an oil pressure or oil condition matter rather than a wear one. Camshaft lobe or follower wear produces a similar note. Check clearances against specification first, since that is measurement rather than guesswork.

It rotates the camshaft relative to its drive sprocket under oil pressure, letting the control unit advance or retard valve timing continuously. Failure comes in two forms: the mechanism sticks or its locking pin fails, producing a rattle at start up and a timing fault, or the oil supply is inadequate because the control valve screen is blocked or the oil is degraded. Test the oil side first, since the control valve is far cheaper than the phaser and often the actual culprit.

Compression testing points at it and a leakdown test confirms it. A cylinder with low compression that does not improve when oil is added to the bore has a sealing problem at the valves rather than the rings, and a leakdown test tells you where: air escaping from the intake means an intake valve, air from the exhaust means an exhaust valve. Exhaust valves burn more often because they run hotter and shed heat only through their seats and guides.

Parts in this category are cheap relative to the work of fitting them, and that ratio should shape how you buy. Keepers, spring seats and valve stem seals cost almost nothing. Valves and springs are modest. Camshafts and phasers are the expensive items, and an oil control valve sits between the two. The current spread appears in the band overhead. Since the head has to come off for most of this work, order the full set of seals and gaskets rather than the single failed item, because the labour is what you are really paying for.

Replace them as a set when you are replacing any. Springs lose free length and rate gradually with heat and cycles, so a single new spring alongside a set of older ones closes its valve with different force, which affects seating at high engine speed and wears its seat differently. They are inexpensive relative to reaching them. Measure free length against specification if you are trying to decide whether an otherwise healthy set needs replacing at all.

Where the seats are worn, pitted or recessed, yes, and that is a machine shop operation using seat cutters to restore both the angle and the contact width. New valves lapped onto worn seats give a poor seal and a short life. Where seats are in good condition and you are simply replacing a valve, careful lapping can be enough. Check the seat width and position after any work, since a contact band in the wrong place burns the valve.

Only where the number agrees. Lobe profiles, journal sizes, the reluctor pattern for the position sensor and the phaser interface all follow the specific variant, and a camshaft with a different profile will run against the vehicle's fuelling and timing calibration even where it fits. Read the number stamped on your own camshaft, match it, and use the quote form where the reference brings back nothing so the factory catalogue is checked properly.

It is the whole story on a variable timing engine. Phasers and hydraulic followers are hydraulic devices operating through very small passages, and degraded or incorrect oil either fails to move them or blocks their filter screens. Many rough running and timing fault complaints on these engines are resolved by an oil and filter change with the correct grade. Use the specified oil, keep to or shorten the interval, and treat a timing fault as a reason to look at the lubricant first.

Yes. Camshafts, valves and springs sell in small numbers on any given engine, so most of this category is handled by enquiry. Quote the reference with the engine code, and say how many pieces you need where the part is per cylinder. Order the valve stem seals as a full set even if only one is leaking, since they harden together and the head is off either way. Where you suspect a phaser, price the oil control valve first. It is the cheaper part, it causes the fault more often, and it can be changed without removing the camshaft.