It is sometimes easy to forget that after all the efforts a cam manufacturer makes in producing his products, the greatest cause of failure is not in the installation or its timing but in the first few seconds and minutes of its active life.
It's a sobering thought but no matter how fine the surface finish or accurate the machining, inevitable imperfections - however slight - will lead to contact high spots at first run. Unless these are carefully ground down in a controlled way in the initial stages of running, these can lead to localised surface overheating, micro-welding and scuffing of the cam lobe surface. Eventually, catastrophic failure later on in the life of the engine could occur. The initial starting of the engine and bedding-in of the cam and its associated components is therefore of critical concern.
Cleanliness and the absence of any foreign matter is surely a given, and in order to ensure surface protection during assembly and timing, cam lobes and journals should be well oiled. Many builders go so far as to use specialised assembly lubricants containing an increased amount of anti-wear additives which, being heavily polarised, physically stick to the surface of the cam during the build. As a general rule it is unwise to introduce additional and unknown additives into the engine since some additives may not be compatible with those in the oil, and will produce precisely the opposite effect of that intended. However, if sourced from the same lubricant manufacture, any potential conflict should be minimised.
Before first fire it is always a good idea to build up the oil pressure, not only in the main oil gallery but also those leading to the valvetrain, and ensure that the lobes are well oiled. For many aftermarket dry-sump oil pumps this is a simple matter of removing the drive belt and priming the oil system by hand. With other systems or engines it may be necessary to crank the engine on the starter motor before firing until full oil pressure is achieved.
Once you are happy that there is enough oil where it needs to be, the engine can be fired, while at the same time taking care not to allow the engine to rev. As a rule, slow running kills camshafts so idling at any point during the break-in stage is to be avoided, but initially around 2000-2500 rpm should be fine. If particularly aggressive cam profiles are in use, it may be better to use softer valve springs during the early stages. If using dual valve springs, simply omitting the inner spring during the build, to be refitted later, will have the desired effect. When running just the single (or softer) spring, remember to limit the speed of the engine to avoid the outset of early valve bounce.
Pre-heated oil often works better than that straight from the can. Not only is it less viscous (and will therefore flow much quicker) but many of the anti-wear additives are sensitive to temperature, and don't actually start to become active until around 60 C. During the running-in stage some people also prefer to use diesel-type lubricating oils. These will generally have a greater detergent/dispersant content than those intended for gasoline use, to cope with the increased amount of soot and particulates expected in the combustion gas. Using diesel oils will therefore be better at trapping any wear metal generated and deliver it to the filter or hold it in suspension where it can do minimal harm. Once fully bedded-in, the diesel oil should be replaced with the race oil and double flushed to minimise any cross-contamination.
As oil quality has improved over the years, some specialist oil manufacturers are beginning to offer specific break-in oils for their customers. Formulated to allow controlled bedding-in of components and with a higher than normal detergency, these must not be used for any serious wide-open throttle work. Furthermore, by keeping to the same supplier, any potential unintended additive interaction can also be avoided. These specialist race oils will have a greater level of anti-wear additive and less in the way of detergents than most other API or ACEA formulations.
Taking care of your cam during its early life will produce dividends later on.
Fig. 1 - Take care of your camshaft
Written by John Coxon