The trend today is for engine designs that will not need what we know as a "tune-up" or in older terms, a "hot-set". "Tune-Up", in Cummins language, is a term used to describe periodic re-adjustments of the valve clearances, crosshead settings, injector settings and engine brake clearances or, taken together, the adjustment of "engine overheads".
The term "hot set" as a matter of interest, derives from the days when rocker housings were made from cast iron rather than aluminium and the overhead settings (injector tension and valve clearances) were quite different depending on whether the engine was cold or at operating temperature. The choice then was to set the overheads when the engine was cold (ie before it has been operated for the day) or alternatively, when the engine was "hot" (defined as 140 degree Fahrenheit oil temperature). True "hot sets" were the dread of mechanics of the time because thermal gloves had not become available and physically handling 140degF is both painful and dangerous.
Over time, "hot set" became a euphemism for "tune-up" or overhead adjustment and the 140degF requirement was forgotten particularly as advanced engine design made that early requirement unnecessary.
The manufacturer makes specific recommendations in relation to the intervals at which these overhead adjustments are to be performed. The intervals vary between engine models.
The Tune-Up will achieve four important outcomes:
Some later engine series have crossheads that require no adjustment and some valve clearances that never need to be touched, however, in the main, an engine has measurable wear in these key areas and periodic readjustment is necessary in order for peak efficiencies to be realized and valve life top be optimized.
Valve clearances can reduce as valve faces and seats wear or they may widen if wear develops on the camshaft that directly activates the valve. Valve clearances that are outside manufacturers recommendations are costing you money in terms of lost power, higher fuel consumption and increasing the potential for engine failure.
Correct fuel injector rocker settings for Cummins PT, Celect and ISX injectors are extremely important. If the setting is too high, excessive mechanical injector cup loadings are likely and will result in failed injector cups and overloaded camshaft rollers and lobes. If it is too low, injector plunger tip carbonising and excessive smoke will result along with potential unloading of the cam roller and camshaft (Top Stop style injectors). If the roller and cam lobe are allowed to have clearance, the cam will be "hammered" and will almost certainly be destroyed prematurely.
Crosshead settings, especially in earlier engines such as NT's and V8's, ensure that the valve pairs open together and that the crosshead guide post is not overloaded sideways. Opening the valves together gives the most efficient cylinder thermal flow control and therefore the higher engine efficiency. Limiting side loading on the guide will prevent it breaking off in the cylinder head casting.
Engine Brakes, whether Jake Brakes, C-Brakes or Inter Brakes, need to have the correct clearances in order for the maximum braking effort to be realized. They also require periodic seal replacement and control valve spring inspection in most applications. This is all part of a Torquepower performed, Tune-Up.
Tune-Ups are not intended, primarily, to give you more available engine power although in many cases that is one of the consequences. Rather, a Tune-Up is a maintenance procedure that ensures you get the best balance or power, performance, economy and longevity from your Cummins product.
If you think your vehicle has not had a Tune-Up for some time, come and talk to us and we'll show you the correct intervals for your model and application. It generally takes from 2 to 5 hours to complete the Tune-Up depending on the model and access to the engine.
We'll even provide you with a Fixed Price before we begin.
Tune-Ups are a very important aspect of your Cummins engine total care.
