Head Case - Tuner Tech

If you are about to replace a leaking head gasket, you may wonder why you almost never see oil or coolant leaking from the gaskets on newer vehicles, even those with plenty of miles on them. After all, that used to make detection of a failed gasket much simpler.

You may also be asking yourself what you can do to avoid head gasket problems in the future. Well, it just so happens Bill McKnight has the answers. He's Director of Training for Victor Reinz - the world's largest supplier of head gaskets, a leading supplier of gaskets to European car makers and a supplier of gaskets to the replacement market.

McKnight tells us all OEM head gaskets installed on modern vehicles are multi-layer steel (MLS) construction. They feature the same elements as the MLS gaskets installed on virtually all vehicles in the '90s, but unlike today's MLS gaskets, those early ones are now known to develop premature oil and coolant leaks.

Why the apparent improvement in head gasket performance over the last 20 years? McKnight unravelled the mystery by first giving us a brief history: "Before '93, most European car makers installed a paper-like, composite head gasket on their engines. By comparison, the newly introduced MLS technology features spring-steel to steel to spring-steel construction, offering many advantages over composite gaskets.

"Unlike composite gaskets, MLS technology contains no paper-like material that can get soft, de-laminate or degrade over time. It won't tear apart with thermal motion during engine operation either. When it comes to strength, newer MLS gaskets are far superior to their composite counterparts.

"Another point in their favor is that MLS gaskets don't require the consideration of a relaxation factor when installing them, unlike composite gaskets. With the composite type, if you tightened the cylinder head to about 60 lb/ft or 80 Newton-meters, and then went back 12 hours later to check, the load would be less because the gasket's paper-type facing would naturally compress and lose some of the load. With MLS gaskets, however, you never find any sign of relaxation because there's nothing soft in them. The layers of MLS gaskets are composed of compressed steel sandwiched by compressed spring-steel. The load you put on an MLS gasket is going to remain the same whether you check it tomorrow, a month from now, or anytime after that," said McKnight.

No longer needing to allow for a 20-35% safety margin to account for this relaxation, Victor Reinz engineers can be more precise when specifying the tightening load for engines. Because the load required to seal MLS gaskets is less than that of a composite gasket, you don't have to tighten the bolts as much. The result is reduced cylinder bore and cam bore distortion. This in turn promotes longer life for piston rings as well as camshafts and cam bearings.

Fine tolerance
While it's clear MLS gaskets offer many advantages over composite parts, those early MLS head gaskets did have one problem - they required extremely fine tolerances between the head and block. Such things are possible on an assembly line, but difficult to duplicate in a workshop or the floor of your garage. This plagued installers and led to the onset of coolant and oil leaks relatively soon after installation, unless everything was perfect.

When MLS gaskets were introduced, they were expensive and radically different from composite gaskets. Engine builders will tell you that before those early MLS gaskets could be installed, the finish of the head and block needed to be as smooth as glass in order for the gaskets to achieve a good seal. McKnight claims that shops were often unable to meet these stringent specifications, but nonetheless, the multi-layer steel quickly replaced all other materials in the manufacture of head gaskets.

Aware of the problem, the Victor Reinz team ultimately solved the fluid leak. The source of the problem was found not to be in the steel sandwich construction, but instead it was the coating used on the steel facings.

This wasn't the first time coatings have caused a headache for gasket manufacturers. Composite head gaskets for the early VW Rabbit, for example, needed to be kept wrapped in their plastic packaging until moments before installation. Otherwise the gasket's coating would quickly harden when it came in contact with moisture in the air.

In the case of MLS technology, the coating formulation is no longer an issue. Owners of new vehicles can expect the OEM MLS gaskets to perform leak-free for the life of the engine. And tuners can also expect to enjoy those same benefits because the gaskets will seal with conventional engine surfaces and tolerances that almost every shop can achieve.

In fact, the average life of an engine has been extended from about 120,000 miles to approximately 200,000 miles since the '90s. That's because the early MLS gaskets were prone to leak at about 80,000 miles. But today, when you install a replacement MLS head gasket on your late-model VW, BMW, Audi or similar, you can expect it to perform leak-free for well over 180,000 miles, provided you take proper care of the engine and cooling system.

For more information on Victor Reinz' MLS head gaskets, visit www.engineparts.com

Before replacing head gaskets, check the cylinder head and block surface for flatness with a straight-edge and feeler gauge. Here you can see a faint line on the head where the outside edge of the old gasket had been. The BMW engine doesn't give much surface area for the gasket to contact the head, making it more difficult for it to seal the combustion gases into the combustion chamber	Here an exhaust manifold gasket is shown upside down. The plate, which is visible, is actually a gasket for sealing the exhaust manifold to the cylinder head. The gasket has a built-in metal heatshield to protect the induction system against exhaust heat. The shield deflects heat so it doesn't vaporize the fuel	In the event of a blown head gasket, the engine's aluminum cylinder head may warp and need to be resurfaced to ensure it's perfectly flat. To do this, the machinist should totally disassemble the head, otherwise the milling machine used to resurface the head will hit and damage any open valves, since there are always some valves open at any given time
After disassembly, check the block (this is from a 325i) for flatness using a straight edge and feeler gauge. The manual calls for decking the block if warping exceeds 0.004"	In preparing to resurface the head, the machinist needs to remove the rocker arm shaft from the head. He does this by pushing the rocker arm shaft through the rocker arms, which allows him to then remove the rocker arms. Here a rod is used to push the rocker shaft through the rocker arms and out the other end of the cylinder head	Before fitting the new head gasket, be certain the top of the block is clean and free of debris, because this could prevent the new gasket from sealing properly, leading to premature failure. And you don't want that
After removing the rocker arm shaft, the machinist will detach the clips and lift off the rocker arms. When all rocker arms have been removed, the valve springs will automatically close the valves, enabling the machinist to resurface the cylinder head without damaging any valves	To tighten the head bolts, first torque all bolts in sequence with a torque wrench for even compression of the gasket. Factory specs then call for tightening the bolts an additional 90. Don't guess; get a torque angle gauge, set the gauge stop to prevent it rotating as you turn, zero the gauge, then turn it 90 using a breaker bar