Born Again

6.6L Du­ra­max LB7 Short-Block Re­build: Part 1

Diesel Power - - Contents - Words by JA­SON GONDERMAN + Photos by JA­SON GONDERMAN

6.6L Du­ra­max LB7 short-block re­build: Part 1

DIESEL en­gines are de­signed to be in ser­vice for a very long time. Be­cause of this, it’s no sur­prise that we of­ten find prime ex­am­ples run­ning flaw­lessly with mileage well into six dig­its. How­ever, with the rise of the diesel per­for­mance in­dus­try has also come more fre­quent re­builds. One camp re­builds due to dam­age, while the other does so to in­crease per­for­mance. We fall into both camps.

The ’02 Chevro­let Sil­ver­ado 2500HD owned by Mon­ica Gonderman (yes, the Truck Trend Net­work’s daily news edi­tor) came with a 6.6L Du­ra­max LB7 engine that had suc­cumbed to a blown cylin­der head gas­ket, burned pis­ton, and munched head by way of poor tun­ing and a throt­tle-happy pre­vi­ous owner. A botched re­build landed the truck in Mon­ica’s drive­way for lit­tle more than a song. While she could have quickly slammed the engine back to­gether with an eBay pis­ton and re­place­ment head, the Gon­der­mans de­cided that with more than 200,000 miles on the odome­ter and fu­ture power goals of more than dou­ble the stock out­put, they will be bet­ter served to tear the engine down and do it right.

For this, Mon­ica turned to the skilled hands at L&R En­gines in Santa Fe Springs, Cal­i­for­nia. L&R is a small fam­ily-run shop that was founded in 1976 in the garage of Larkin Ran­ney and his wife Rob­bie. Now, 41 years later, the busi­ness is still a fam­ily af­fair, with sons Derek and Brent join­ing their par­ents for the daily grind of op­er­at­ing a highly suc­cess­ful engine-build­ing en­ter­prise. L&R can han­dle any­thing from clas­sic flat­heads to large ma­rine diesels and has a par­tic­u­lar spe­cialty in build­ing per­for­mance Du­ra­max en­gines.

L&R first dis­as­sem­bles the dirty short-block, then gives the core a much-needed wash in the hot tank be­fore Mag­naflux­ing it to check for hair­line cracks and ir­reg­u­lar­i­ties that could pose is­sues down the road.

Af­ter clean­ing and in­spec­tion, the cylin­ders are bored and honed, the main bear­ing bores are line-honed, and fi­nally the deck sur­face is milled. This all en­sures the block is per­fectly square and ready to run for an­other quar­ter-mil­lion miles. Af­ter in­stalling new freeze plugs and a quick coat of paint, the block is ready for re­assem­bly, which we’ll re­view in a fu­ture re­port.


The engine was taken to the Du­ra­max ex­perts at L&R En­gines in Santa Fe Springs, Cal­i­for­nia, where it was stripped down and re­ceived the full prep treat­ment (clean­ing, ma­chin­ing, and such).


Frank, an L&R engine spe­cial­ist, has been build­ing en­gines nearly his en­tire life. Be­fore start­ing the re­build, he gives the block a good clean­ing. Brake cleaner and a rag work won­ders for re­mov­ing any re­main­ing ma­chin­ing oil and residue.


Du­ra­max en­gines use oil squirters to pro­vide cool­ing for the pis­tons . These small tubes are af­fixed to an oil gal­ley with banjo bolts and pro­vide a con­cen­trated blast of oil di­rectly to the bot­tom of the pis­ton.


Clean­li­ness is of ut­most im­por­tance when build­ing any engine. Frank takes the time to clean ev­ery part—even down to the bolts—be­fore re­assem­bly. Here the camshaft re­ceives a hot bath be­fore be­ing lubed for in­stal­la­tion. The stock cam is reused be­cause it works ex­ceed­ingly well for the power level

(650 hp) Mon­ica and Ja­son are shoot­ing for, but also be­cause not many af­ter­mar­ket re­place­ments ex­ist.


In­ter­est­ingly, L&R reuses the fac­tory cam bear­ings. Build­ing one to two Du­ra­max en­gines a week, Derek says they have yet to come across a failed fac­tory bear­ing. He be­lieves the stock hard­ware is made bet­ter and stronger than pieces that are avail­able in the af­ter­mar­ket.


One of the most com­mon fail­ure points on Du­ra­max en­gines is the cam-gear re­ten­tion pin. This tiny dowel pin is fully re­spon­si­ble for keep­ing the camshaft timed to the engine’s ro­ta­tion. Sur­pris­ingly, we found the pin had ob­longed its mount­ing hole in the camshaft, and it lit­er­ally fell out. The re­built engine would have been mo­ments away from cat­a­strophic fail­ure had this prob­lem not been dis­cov­ered.


The so­lu­tion to the dowel pin is­sue is to ma­chine a pocket in the camshaft and in­stall a 5mm woodruff key. Com­monly re­ferred to as “key­ing the cam,” the woodruff key al­lows the cam tim­ing gear to at­tach with no mod­i­fi­ca­tion and will stay in place even at the most ex­treme power lev­els.


Back at the wash tank, Frank pre­pares the lifters for in­stal­la­tion. The rollers on the lifters are es­pe­cially sus­cep­ti­ble to con­tam­i­na­tion, so it’s im­por­tant they go back in clean.


A heavy coat of as­sem­bly lube is ap­plied to each lifter. This thick lubri­cant helps en­sure no dam­age is caused to the lifter or camshaft upon the ini­tial start-up, be­fore the oil­ing sys­tem reaches full pres­sure.


Insert­ing the lifters into the engine is as much an art as it is a sci­ence. Each pair is held in place with a guide plate and keeper as­sem­bly and needs to be per­fectly aligned for the setup to at­tach prop­erly.


With the camshaft and lifters in place, Frank turns his at­ten­tion to pre­par­ing to in­stall the crank­shaft. The Cle­vite H-Series main bear­ings be­ing used fea­ture en­larged cham­fers at the sides for greater crank-fil­let clear­ance and are pro­duced with­out flash plat­ing for bet­ter seal­ing.


Lay­ing the crank­shaft is a two-per­son job due to its size and weight. The crank needs to be low­ered into the block as straight and level as pos­si­ble to pre­vent any dings or scratches to the pol­ished bear­ing sur­faces.


An­other Du­ra­max engine fail­ure point is at the crank­shaft. While it’s ex­tremely rare, Du­ra­max cranks are known to break near the first coun­ter­weight. This of­ten hap­pens when peo­ple in­crease power and rpm but don’t prop­erly bal­ance the ro­tat­ing as­sem­bly. The crankshafts also suf­fer from the same is­sue as the camshaft’s dowel pins and are of­ten keyed as well.


In an ef­fort to in­crease bot­tom-end strength, the stock main-bear­ing bolts are ditched in fa­vor of ARP studs. Each stud is threaded in by hand be­fore be­ing cinched down with an Allen head socket to en­sure it is in­stalled to the proper depth.


With the studs in­stalled, Frank carefully low­ers each of the main-bear­ing caps into place. These caps need to be in­stalled in the same po­si­tion and same ori­en­ta­tion they were re­moved from, and care needs to be taken not to dam­age the stud threads while low­er­ing the cap into place.


Af­ter ap­ply­ing co­pi­ous amounts of ARP’s Ul­tra Torque lubri­cant, Frank torques the main-cap studs to 175 ft-lb and the cross bolts to 90 ft-lb in the proper se­quence.


In ad­di­tion to the ver­ti­cally ori­ented studs, Du­ra­max en­gines also use re­tain­ing bolts that run hor­i­zon­tally through the block on ei­ther side of the main-bear­ing caps. They are in­cluded with the stud kit and torqued to spec­i­fi­ca­tion af­ter the studs are se­cured.


With the crank­shaft in­stalled, Frank turns his at­ten­tion back to the camshaft by bolt­ing the re­tain­ing plate into place. This can be done at any time, but it ac­tu­ally co­in­cides with the next step.


Af­fix­ing the camshaft tim­ing gear and align­ing it with the crank­shaft is the fin­ish­ing task for cam and crank in­stal­la­tion. Du­ra­max en­gines uti­lize a gear-driven tim­ing sys­tem in­stead of belt or chain ar­range­ments, and the camshaft is driven di­rectly by the crank­shaft.

Upon find­ing a burned pis­ton and a poor at­tempt at a re­pair and re­assem­bly, Mon­ica and Ja­son Gonderman made the tough de­ci­sion that the 6.6L Du­ra­max LB7 engine in Mon­ica’s ’02 Chevro­let Sil­ver­ado 2500HD needs to come out. And be­cause the truck has more than 200,000 miles on it (the ac­tual mileage is still a mys­tery) and the plan is to achieve a power fig­ure that will push the lim­its of the stock in­ter­nals, a full re­build is in or­der.

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