Fire rings, head studs, valve train up­grades for 6.7L Cum­mins

Ultimate Diesel Builder's Guide - - Contents -

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.

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