Part Number: TMZ-4G63-Head-Dowel-(size)
Quantity: 10 Dowels Per Set
(Head Studs and Head Gaskets Sold Seperately)
These are specially machined 4340 Pre-Hard Chromoly Alloy Steel shouldered dowels that are designed to be inserted into the cylinder head at the head stud locations to reinforce the cylinder head casting and prevent crushing of the casting under high boost pressure applications. The inserts sit below the head stud washer, and allows the torque applied to the head stud to be properly distributed into the cylinder head casting. It also will reduce the issue of elongating the head stud holes from using a 7-bolt DSM motor with 6-bolt DSM cylinder head and 11mm studs. With the larger 1/2″ inserts installed you can use the potential of the stud without worries of crushing your cylinder head casting.
The cylinder head bosses must be spot faced and then the head stud holes are bored with an SAE-sized tool to fit the OD listed below, then the dowels are press-fit / tap-fit installed. With 1/2″ head studs, the engine block and cylinder head both get machined, and the 4G63 7-bolt blocks can be tapped to 1/2″ without any issues. The 6-bolt applications require (10) 1/2″ “Time-Serts” to be installed into the block by the machinist.
11mm uses a 0.625″ OD on the dowel. Uses 11mm head studs. Uses 5/8″ boring tool.
12mm uses a 0.656″ OD on the dowel. Uses 12mm head studs. Uses 21/32″ boring tool.
1/2″ uses a 0.6875″ OD on the dowel. Uses 1/2″ head studs. Uses 11/16″ boring tool.
The shoulder OD is 0.940″ on all versions.
These are also great repair parts for cylinder heads that have seen elongation or crush on the seats that is repairable so you don’t have to toss your cylinder head in the garbage if this scenario happens; a likely one when you are running a high boost application.
*Note: With Evo 9 MIVEC cylinder heads, you must drill the head dowels to allow for the oiling ports, or drill through after they are installed. You will destroy stuff if you do not do this!!