TECHNICAL NEWSLETTER. Hydraulic lifter noise diagnosis.
Several causes of lifter noise exist.
SYMPTOM: Noise is there at start up and will not go away under all conditions. Noises will start when the wear, in the mechanical parts between the valve tip and the lifter, can no longer be compensated for by the hydraulic lifter pumping up to adjust. This more commonly relates to an old engine.
Areas to inspect are valve tips, rocker arm tips and the saddles or pivots of the rockers. It is not common to find damaged pushrod ends; but check these also.
Should the noise develop with a recently reconditioned engine, particularly if this starts when being tuned on a chassis dyno, check for a damaged camshaft lobe. Most common will be when using a solid camshaft profile. The choice of a solid camshaft is made when the budget doesn’t allow for the safer roller cam.
Less common will be a small foreign particle that has been fed into a lifter by the lubrication system. If this has occurred at the first start up of a new engine, run it for a test period until it clears, or, failing this, when the decision has to be made to change the lifter.
With the later model lifters fitted to overhead camshaft engines, neoprene seals within the lifter can harden and their leakage rate deteriorate until the oil supply can no longer keep up with this leakage and the lifter bleeds down. Typically, the engine may have been overheated, or running at above normal temperatures for a period, and these lifter seals have been damaged. Expect the exhaust lifters to suffer most. Heat coming up the valve stem will be a factor.
Where the noise occurs after just fitting a timing belt, is very noisy and at an even level in all cylinders, check the camshaft timing. The valves may be hitting the pistons.
Where the noises are general, and the head has just been fitted following a recondition, this may only be the short time it will take to bleed the lifters up after we have bled them during our reconditioning procedures. We do this because many of the multi valve head designs run the valves very close to the pistons. This eliminates the off chance that a pumped up lifter holds a valve off it’s seat and strikes a piston at the first turn at start up. The bleed up may take a few minutes and will improve during this period as each lifter pumps up after the oil supply to the head displaces the air inside the oil gallery in the head. Note that due to the need for absolute cleanliness with the variable camshaft mechanisms, our reconditioning procedures are to remove the oil gallery plugs from these heads for proper cleaning. Inevitably, air will exist within the gallery system and it will be displaced by the oil feed at start up.
SYMPTOM: Noise starts several minutes after start up and will not go away until after the engine is shut down for five minutes and restarted again. The engine restarts quietly as before but after a few minutes the noise returns. Suspect an oil supply problem immediately and investigate. Do not test drive. Do not suggest to the owner to “run it for a few days”. pull the oil filler cap and assess the condition of the oil. Put a master gauge on it and see what,s going on. It is common for the multi valve engines to suffer badly from missed oil changes. The oil clearances in these engines are much smaller than in the older American engine designs. Partial blockages within the oil gallery system, from oil pick-up screen right up to the fine filters now found in the heads of the variable cam designs, will restrict oil flow to the lifters.and even to the point of starving the crankshaft-bearings. The inevitable seizure will occur. This will start at noisy lifters then oil starvation to the main bearings and then quickly to the camshaft and con rod joumals as the main bearing metal circulates around the system. Treat this symptom seriously.
Equally serious, and with the same symptoms, is a dent in the sump that has masked the oil pick up screen. This will run fine at idle speeds but once road speed is reached, the restriction will cause the pump to draw an insufficient volume of oil to cover the normal volume losses from all the bearings within the lubrication system. Lifters will then start to bleed down and the noises will start.
SYMPTOM:Noise is intermitant under all conditions.
Mechanical wear to one of the component parts can cause the lifter to pump up, noise then goes away, until the wear comes back into play causing the lifter io bleed back. The noise is the interim time taken for the lifter to readjust. A minor element of running in of a reconditioned engine can have a period of this; particularly where the rocker system uses bridges or pivots . (older American engine designs)
SYMPTOM: Noise is there at start up but goes within several seconds and is not there again until after another engine rest period of 24 hours for example.
This is often diagnosed as result of a bled down lifter or two that have held a valve off it’s seat over night. However, the factors that come into play here are numerous: Some lubrication systems will bleed back over night and leave an air space inside the oil gallery. Until this air is displaced, several lifters can quickly bleed down until the pressure of air and oil reaches them. Should air get into the lifter, then some noise can occur until the oil displaces it.
Where a modified engine is involved, yet other factors come into play. Consider camshaft profiles, valve spring rates, make of oil filter, oil restrictor kit or other oil gallery modifications, and even the grade of oil. Until operating temperatures are reached, and given that the noise is correctly diagnosed, reserve judgement until the engine design settles down at the right temperature when acceptable levels of noise should then exist.