Magazine for the auto service professional
Issue link: http://asp.epubxp.com/i/684411
Circle 120 on Reader Service Card Technical would take 2,800 hours to drive 200,000 miles. So, 2,800 hours, times 72,000 times per hour, is 201,600,000 times! Tis means, of course, we have compressed then relaxed the head gasket material 201,600,000 times!" Since a bare stainless steel gasket surface would have a difcult time in sealing against even the fnest machined surface, a special- ized coating is applied to the outer surfaces that aids in flling microscopic voids in the deck surface fnishes. As Fel-Pro Product Manager Ron Rotunno points out, in the early days of MLS head gaskets, the seal coating was somewhat sticky, which prompted handling cautions, advis- ing installers not to remove gaskets from their packaging until immediately prior to installation. "Te concern was that contaminants such as airborne particles or transfer from dirty fngers, etc., would stick to the surfaces, pos- sibly preventing an ideal sealing surface," says Rotunno. Te coatings used today by leading makers of MLS head gaskets do not feature a super-sticky rubber, so it's OK to expose the gaskets to the air at any time. According to Rotunno and McKnight, today's coatings, depending on the specifc application, may consist of advanced polymers and/or FKM Viton. While early generations of coatings demanded an extremely fne surface fnish, today's coatings are capable of sealing even on less-than-ideal surfaces, allowing compatibility with slightly rougher Ra fnishes. Cylinder block deck and head deck surface fnishes are commonly graded on a roughness-average (Ra) scale, with a lower Ra indicating smoother and a higher Ra as less- smooth. For instance, an Ra 5 would indicate an extremely smooth, almost mirror-like fnish, while an Ra of 100 would indicate a rougher machined surface. Today's advanced MLS gaskets are more