At H.A.M. we take a value-added approach to cylinder head rebuilding. It’s our commitment that your heads will be ready to install as shipped. We deal with all of the pesky details that other shops either ignore/don’t notice and leave for the customer to deal with or want to upcharge for. If your heads are from the M96/97 or 9A1 line that commitment extends beyond the cylinder head itself to include the valve covers and cam bearing caps. Our base price includes cleaning and detailing the valve covers and cleaning the cam bearing caps so you can install them right out of the bag. It’s best to think of the heads and these parts as a unit, all of which need attention during service and should be kept together at all times.
When it comes to M96/97 cylinder heads we have been the global leader in reliability, R&D, repairs and performance since we began working with them back in 2007. We are the choice of leading professional engine builders and shops who want only the best. We are happy to consult with each customer to make sure you know your options and get the most out of your engine. And because we are a micro business that doesn’t have a sales staff or secretary, your pipeline to us is direct with no middleman.
All M96/97 exhaust flanges are refaced as part of our base service. Because of the secondary air injection passage arrangement the flanges see very high temps with hot spots that cause waviness that can cause an exhaust leak. The steel factory exhaust gaskets usually etch the surfaces and on later heads we often see erosion around the entrance to the large secondary air passage (the single big one that cuts through the head). This erosion can be severe enough to require welding to build up the surface. Throw in some corrosion and it’s clear that the exhaust surfaces on these heads need a fresh surface. The 9A1 heads don’t have this SAI passage arrangement and therefore don’t suffer with this issue so refacing isn’t part of the base service price, but if the surfaces are damaged or corroded refacing is available.
Of course all head gasket surfaces are diamond milled for a perfect finish that exceeds factory specs.
All 3.4 987, 3.6/3.8 996/997 heads get new valve guides and valve seats. Click here for a detailed explanation of why we insist on this preventative service for these heads. All other M96 heads are typically easy on valve guides and we have yet to see a seat drop on any of them so we are okay with servicing them without replacing the seats and guides if stock performance is acceptable. If you want to kick performance up to another level, we can machine the factory valve seats with flow tested Serdi profiles, though for precision we do insist on replacing the valve guides so we can finish them to fit our Serdi pilots perfectly.
It’s worth noting that while reliability is the primary reason for replacing the valve seats on 3.4 987, 3.6/3.8 996/997 heads there is also a significant performance benefit. We install blank seats that we then machine from scratch with Serdi blades that we selected after flow testing. Because the ports on these heads are stout performers in stock form, we can make very nice flow gains with the right seat profiles and our ultra precise machine work. The valves sit proud (not sunk) in their new tight-fitting seats which greatly improves flow around the valve and aids in the critical pressure recovery period.
All valves are carefully cleaned (no small parts tumblers! They are fast but hard on stems) and inspected. Fortunately the O.E. valves are super durable and we have never seen one fail, with the exception of keeper fretting on abused track cars. Click here and scroll down for a picture of this condition. Once the valves pass inspection they are ground on our centerless valve grinder with a T.I.R. of 0.0000″ – 0.0001″. A much tighter tolerance than factory. In performance applications we back-cut the intake valves. And the angles we use are not random or selected from the common angles most machinists have used for years. Many years ago we did extensive testing on this subject and have found very specific angles that work best when combined with the seat profiles we work with. We leave no stone unturned when it comes to reliability and performance.
996TT heads are wonderful, durable heads. We have never seen them drop seats, but they are brutally hard on valve guides. Our service for these heads mirrors the service we offer for M96 heads with guide replacement. Unless the exhaust flanges are corroded they typically don’t need refacing but we are happy to do so if needed.
Click here for specific info about the services that go into our aircooled 911 heads.
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