BOMB PROOF TOP END
Fire rings, head studs, valve train upgrades for 6.7L Cummins
No matter the power plant, the natural design of the internal combustion engine—where the cylinder head(s) bolts to the block—lends itself to eventual head gasket failure. While not quite as frequent as the failures you see on other engines (the 6.0L Power Stroke or LLY Duramax, to name a few), blown head gasket scenarios are surprisingly common on the 6.7L Cummins. Some believe head gasket failure occurs more often with the 6.7L due to it building more cylinder pressure (i.e. torque) than the 5.9L mills did. Others contend that the 6.7L’s larger bore lessens the available sealing area between cylinders and water jackets when directly compared to the 5.9L.
No matter the cause, a head gasket job always warrants a look at “upgrading” things so the failure doesn’t occur again. When this ’09 Dodge Ram 3500 came into Flynn’s Shop in Alexander, Illinois, with a pressurized cooling system, the owner knew he wanted to fix the problem permanently. For that, the head would take a trip over to Scheid Diesel to be resurfaced, fire-ringed, fitted with threaded freeze plugs, and equipped with performance valve springs. A set of Scheid’s Stage 1 push rods and ARP Custom Age 625+ head studs would finish off the parts list. Follow along for the ultimate tutorial on how to bulletproof the top end of a 6.7L Cummins. UDBG
This is what the 6.7L Cummins cylinder head looked like after the folks at Scheid Diesel got their hands on it: resurfaced and cut for fire-rings. The fire-ring process is something Scheid Diesel has all but perfected over the years, and when the finished product gets installed, there are no maintenance concerns after the fact. This means that—contrary to the belief that firerings are for competition-only purposes— fire-rings are perfectly acceptable for daily drivers, tow rigs, and of course, high performance trucks if done correctly.
The fire ring grooves in the head are cut between 0.040-inch to 0.041-inches deep, while each ring encompasses a 4.340-inch inside diameter. As for the head gasket, a factory 6.7L MLS unit is used, albeit with the center rings removed (to make way for the fire rings).
Made from mild steel, the fire rings themselves are 0.105-inches thick. Once crushed between the head and block (and sitting in their respective grooves in the head,) a much stronger seal is employed to help contain excessive cylinder pressure.
Oversized valve seats were also pressed in while the head was at Scheid’s. The larger valve seats are installed so that, when the head heats up and expands, the seat won’t drop out (which is known to happen from time to time when the factory seats are still in place).
To accompany the oversized valve seats, the valve springs were also upgraded. A set of 110-pound springs sit in place of the stockers, and should be good for elevated boost and drive pressure levels, in addition to handling higher rpm.
As an added insurance measure, Scheid ditched the factory (pressed-in) internal freeze plugs in favor of the thread-in style. At elevated power levels, the 11 internal freeze plugs within the top side of the head are all fair game for blowing out. And when one does, coolant disappears quickly, while mixing with engine oil at a rapid rate. The threaded freeze plug method all but rules out this possibility and makes sense to do anytime head removal is necessary.