Diesel World – October 2019

(Jacob Rumans) #1
WithhighmilesandprolongedexposuretoexcessiveEGT,it’snotuncommonfor24-valvecylinderheadsto
crackvalveseatsorevendropthemaltogether,whichcanspelldisasterinatleastonecylinder,if notforthe
entireengine.Toeliminatethispotentialproblem,Fleeceinstallshardened,oversizedvalveseats(inboththe
exhaustandintakesides)thatfeaturea radius’dedgeonthesidethatinstallsfacedownwithinthehead.

TECH COMPETITION-READY, OFF-THE-SHELF AVAILABILITY

 Like any other engine-related operation, Fleece relies on good usable cores to provide
the lifeblood for its Performance cylinder head program. And because the quality of any
core head Fleece receives is unknown initially, each head is stripped (valves, springs,
seals, guide liners, freeze plugs), thermal cleaned and shot-blasted, and undergoes a
thorough inspection before being qualified as usable.

 For maximum combustion sealing between the block and head,
Fleece cuts fire rings into the fire deck of every Performance series
head it sells (all fire-ring protrusion exists in the head). This high
horsepower insurance policy ensures, with the help of a quality head
fastener, that boost pressures in excess of 80-psi can be run without
worry of blowing a head gasket. A fire-ring head gasket kit with a
multi-layer steel gasket and 4.550-inch diameter mild steel rings
accompanies each Performance head.

 Before leaving the confines of the Haas VF-4SS, the head is
machined to accept screw-in type pipe plugs in place of the 11 freeze
plugs located internally on the exhaust manifold side. High horsepower,
high miles, and old age can lead to the factory freeze plugs blowing
out, which allows coolant to mix with engine oil. Every cylinder head
that passes through the doors at Freedom Racing Engines is treated to
screw-in freeze plugs.

After measuring the starting thickness of the core head, the extensive job of
transforming it into a Performance version begins with the decking process. Within
Fleece’s Haas VF-4SS VMC (vertical milling center), 0.003 to 0.005 inches of material is
removed during a typical resurfacing, with the exact measurement being recorded on each
head’s data sheet upon completion. We’ll note that the head we followed from start to
finish was a unit off a 6.7L Cummins.

The next stop for the Performance series head brings it to the valve seat station, but before the oversized
valve seats are installed, the head’s cast-in valve guides are treated to fresh valve guide liners. The K-Line
bronze valve guide liners incorporate a spiral pattern that aids lubrication. After they the liners are in place, a
broaching process expands them, essentially locking them in place within the valve guides.

78 OCTOBER I 2019 • DIESEL WORLD http://www.dieselworldmag.com

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