Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/684411
54 | ASP June 2016 Technical While applications for composite head gaskets continue to exist, the majority of production and performance engines now use MLS (multi-layer steel) gaskets. MLS head gaskets MLS cylinder head gaskets have been employed by OEMs since about 1991 (with Ford and Mitsubishi) and are commonplace in OE engines today. Unlike a composite gasket, MLS gaskets are constructed of multiple layers of hardened stainless steel, featuring embossed outer "active" layers and "passive" or "stopper" inner layers. Te embossed layers are raised areas that provide sealing, with the stopper layers providing both a dead-stop during clamping (which prevents over-compression), as well as the desired gasket thickness. Te assembly, which may feature three to fve layers depending on the application, is secured together with rivets. Te embossed active layers compress and expand during engine operation as the cylinder head tries to lift of of the deck during combustion, essen- tially acting as tensiled springs to maintain constant sealing contact between the head and block deck. Bill McKnight, MAHLE – Clevite and Victor aftermarket training manager, ofers a way to visualize the task of the head gasket. "What happens as an engine runs is that the cylinder head is actually lifted of the block from the fring pressure in the cylinder," he says. "It's hard to imagine this, but the head bolts are elastic and stretch a bit to allow this head lift-of. "Te MLS gasket actually acts as a spring, relaxing, then being compressed again every time the cylinder fres. If you drove your car at 70 miles an hour for 200,000 miles and it ran a steady 2,400 rpm, the cylinders would each fre 201,600,000 times. "Te math is simple: 2,400 rpm means each cylinder fres 1,200 times a minute (two revs of the crank for each fring) times 60 minutes per hour is 72,000 times in an hour. At 70 mph it As the rear engine cover is installed, the nylon seal guide centers the seal to the crankshaft fange and falls out once the seal engages. This prevents the seal lips from peel- ing rearward. Do not add any additional chemicals to either side of an MLS head gasket. Today's sophisticated MLS gaskets feature coatings that seal minute deck surface machined fnishes. All threaded fasteners must be tightened to spec- ifed value, but this is extremely critical for main cap and cylinder head bolts. Where torque-plus- angle tightening is specifed, using an electronic torque wrench that accomplishes both torque and angle saves time and increases accuracy. Today's electronic torque wrenches provide both visual and audible alerts as your desired torque values are approached and obtained.