Eric Sch­miege’s Rat Ate a Nut. We Cured the Sick Short-Block, but Top End, Oil Pan, and Drive­abil­ity Is­sues Still Need Fix­ing.

Hot Rod - - Hotrodtotherescue - Mar­lan Davis Jeff Smith


When the big-block Chevy in Eric Sch­miege’s 1965 Bel Air swal­lowed a nut, it cracked a cylin­der wall and dam­aged a pis­ton. Fur­ther anal­y­sis by for­mer HOT ROD ed­i­tor Jeff Smith re­vealed an out-of-square block with ex­ces­sive cylin­der-wall ta­per and ex­ces­sive main and rod bear­ing clear­ances. Last month, Jim Grubbs Mo­tor­sports sleeved the cracked cylin­der, bored the en­gine 0.070-inch over, and rema­chined the block to square it up. Smith then re­assem­bled the block, in­stalling new SRP forged pis­tons and premium rings. He also re­placed the Bel Air’s old hy­draulic flat-tap­pet cam with an Isky hy­drauli­croller pro­file that bet­ter matches the Bel Air’s driv­e­train gear­ing and Sch­miege’s driv­ing style. How­ever, pis­ton deck height, val­ve­train, oil sys­tem, and drive­abil­ity is­sues still re­mained to be dealt with.


On steel-rod en­gines, high-perf big-block Chevy builders usu­ally shoot for near-zero pis­ton-to­block deck heights (the pis­ton deck is about flush with the block deck at top dead cen­ter, or TDC). With typ­i­cal 0.038–0.041inch com­pressed-thick­ness com­po­si­tion head gas­kets, this achieves good quench with the Rat mo­tor’s com­plex com­bus­tion cham­ber and still leaves an ad­e­quate pis­ton-to-head, high­rpm clear­ance safety mar­gin.

That was cer­tainly Smith’s orig­i­nal in­tent, but, as he ex­plains, “Be­fore we sent the block out to Grubbs for re­pair and ma­chin­ing, we checked the old pis­ton-to-deck clear­ance and found the block decks were not even close to square. They were out al­most 0.008 inch rel­a­tive to the crank cen­ter­line front-torear with the front por­tion high, which is why we had Grubbs mill the block to square it up. But now when we went and in­stalled the new pis­tons, we dis­cov­ered they were stick­ing up out of the block by about 0.013 inch on av­er­age, prob­a­bly be­cause the deck had been pre­vi­ously milled in a prior re­build, but not rel­a­tive to the crank cen­ter­line. For­tu­nately, Fel-Pro saved our ba­con with its 0.053- inch com­pressedthick­ness M LS[ multi layer steel] Per­maTorque gas­ket that also of­fers su­pe­rior seal­ing po­ten­tial

with the proper deck sur­face fin­ish. If our deck was zero, we would have used an 0.041 head gas­ket, and the com­pres­sion would have been al­most ex­actly the same.” Even with all the deck and head milling, pis­ton-to­valve clear­ance was still more than am­ple, com­ing in at 0.190 inch or higher at the clos­est ap­proach for both the in­take and ex­haust valves.


Isky’s new hy­draulic-roller cam re­quired a com­ple­men­tary valvespring and re­tainer up­grade. As for the lifters, Smith went with Isky’s “real Mc­Coy” John­son short-travel retro­fit units with paired guide bars. With proper preload, shorter lifter travel of­fers more high­rpm sta­bil­ity com­pared to stan­dard-travel hy­draulics.

Smith bolted the heads onto the block us­ing ARP per­for­mance head bolts and pro­ceeded to estab­lish the val­ve­train ge­om­e­try. “I like to use that old trick, where with the lobe on the cam base cir­cle, you want to place the roller tip-to-pushrod con­tact point at roughly one-third in from the pushrod side of the valve stem tip. This pushes the rocker tip across the cen­ter­line at max lift and then back again. At max lift, the cen­ter of force should ide­ally be ex­erted on the cen­ter of the valve tip.

“To get there, we needed pushrods that were shorter than rec­om­mended, prob­a­bly be­cause the heads and deck had been cut so many times. Us­ing an ad­justable pushrod, we ended up spec’ing 7.600-inch for the in­take and 8.550 for the ex­haust side. These can be spe­cialordered from Isky, but there is a two-week wait, so Isky sent us a set of 7.650 and 8.600 lengths they had in stock.

“I looked at the con­tact point with the pushrods still ‘off ’ a lit­tle, and it looked OK—not ideal, but ac­cept­able. I think this shows with a stud-mount rocker, you can be off 0.050 inch or so and still be OK—at least on a mild street car.”


Smith also took the time to ad­dress some an­noy­ing prob­lems Sch­miege had been liv­ing with be­fore the ma­jor en­gine fail­ure brought things to a head. The Bel Air had been low­ered 2 inches with dropped spin­dles, caus­ing the ex­ist­ing oil pan of un­known pedi­gree to bounce

and rub against the steer­ing drag link. Smith re­placed the pan with a Milodon 6-quart pan; listed for a 1957 Chevy, the sump doesn't ex­tend as far for­ward, pro­vid­ing more clear­ance. It re­quired a match­ing Milodon pickup and screen as­sem­bly. With a new pickup, Smith fig­ured he’d may as well re­place the old oil pump with a Milodon high-vol­ume/ high-pres­sure pump.


That left only the Bel Air’s part-throt­tle ping, which could have been caused by any com­bi­na­tion of too-high com­pres­sion, a mis­matched cam, an overly ag­gres­sive spark curve, or carb mis­cal­i­bra­tion. The first two items were ad­dressed dur­ing the en­gine re­build, so af­ter bolt­ing on Sch­miege’s old Offy du­alquad in­take, 600-cfm Hol­ley carbs, and MSD dis­trib­u­tor (Isky’s roller cam doesn’t need a spe­cial drive gear), Smith set up

“I would not charge less than $1,000 [in la­bor] to build an en­gine like this. I have over 50 hours of time in it, in­clud­ing as­sem­bly. That’s only $20 per hour. I’d be bet­ter off work­ing part-time at In-N-Out!”

— Jeff Smith

MSD dis­trib­u­tor (Isky’s roller cam doesn’t need a spe­cial drive gear), Smith set up the en­gine on his Sum­mit test stand. “We pre­set the tim­ing at 12 de­grees BTDC and used the elec­tric fuel pump on the stand to pre­fill the car­bu­re­tors. We hit the ac­cel­er­a­tor pumps about four times and then let the fuel va­por­ize for about 30 sec­onds be­fore at­tempt­ing to start the en­gine. It started im­me­di­ately.

“But we had an idle-qual­ity is­sue that ini­tially made it hard to main­tain rea­son­able ini­tial tim­ing un­der 1,000 rpm. We found the ad­vance curve in Sch­miege’s MSD dis­trib­u­tor came in way too quickly: all in by 1,100 rpm. In­stalling a heav­ier cen­trifu­gal ad­vance spring slowed the curve down, let­ting us achieve a smooth idle at 850 rpm while also cur­ing the car’s pre­vi­ous part-throt­tle ping. We stayed con­ser­va­tive, lim­it­ing to­tal ad­vance to 33 de­grees with MSD’s blue stop-bush­ing and our ini­tial 12 de­grees tim­ing.

“We wanted to break the new rings in prop­erly, so we lim­ited the time on the test stand to 10 min­utes. With the en­gine in the car and no leaks, we put the en­gine on the road at light cruise un­til oil and wa­ter temp nor­mal­ized,

10 min­utes of driv­ing, we hit it to WOT [wide-open throt­tle] for a few sec­onds and al­lowed it to pull back down. This al­lows the rings to seat prop­erly.”


Sch­miege was able to drive the car home to San Diego from Smith’s north­ern Los An­ge­les shop that same af­ter­noon af­ter the en­gine had first been fired, a 4½-hour drive in traf­fic, with no drive­abil­ity glitches and no cool­ing is­sues. With 16 inches of idle vac­uum, the power brakes work great. When Sch­miege gets on it, the Isky hy­draulic roller cam’s broad torque curve is well matched to the big full­size Bel Air. “It drives like a champ, bet­ter than it did be­fore,” Sch­miege says hap­pily. “I’ve got my car back me­chan­i­cally!” The only glitch: “Idle oil pres­sure is a bit higher than I would like,” Smith says. “With oil up to temp, it idles at 55 to 60 psi with Lu­cas 10W-30 oil. So we will change it to 5W-20 when it’s time for the next oil change. I am try­ing to avoid load­ing the dis­trib­u­tor gear when the en­gine is cold with high oil pres­sure, which now is as high as 80 psi.”


Don’t rush. Per­form mock-ups with the parts you will ac­tu­ally be us­ing dur­ing the fi­nal build. “Get­ting all these lit­tle de­tails right de­mands hours of work to re­solve,” Smith says. It may take 50 hours or more to as­sem­ble an en­gine to the qual­ity stan­dards shown here— and that’s just for a mild street hot rod mo­tor!

01] Stronger, big­ger, and bet­ter, the now-469ci big-block Chevy drops back into the 1965 Bel Air. You’d think there’s plenty of room in a full­size Chevy, but Smith says, “It was dif­fi­cult to get the en­gine in and clear the carbs with just a sin­gle-chain hoist. We could have used one of those en­gine-tilter chains with the ad­justable lev­eler.”

[ Among the re­main­ing is­sues: With the Bel Air’s front-end low­ered 2½ inches, the ex­ist­ing oil pan kept bounc­ing off the drag link.

[ Car owner Eric Sch­miege read­ies the mo­tor for run-in on a Sum­mit test stand, com­plete with pres­sur­ized cool­ing sys­tem and full ex­haust.

[ The Chevy Rat in Sch­miege’s 1965 Chevy Bel Air died. Last month, we fixed the short-block. Now, we’ll fix the re­main­ing prob­lems.

02–04] SRP’s pis­tons were 0.013 inch above the block deck atTDC ( 02), caus­ing both ex­ces­sively high static com­pres­sion for pump gas as well as in­ad­e­quate pis­ton-to-head clear­ance. Fel-Pro came to the res­cue with its thick, 0.053-inch com­pressed-thick­ness MLS head gas­ket ( 03), yield­ing a friendly 0.040-inch pis­ton-to­head-deck clear­ance value. It also re­duced the com­pres­sion ra­tio to a pump-gas-friendly 10.03:1 with the Edel­brock heads’ 108–109cc cham­bers (as mea­sured by Smith, 04). To use an MLS gas­ket, both the head and block deck sur­faces must be mir­ror-smooth like they were on Sch­miege’s newly ma­chined parts. Fel-Pro of­fers MLS Rat-mo­tor gas­kets in 0.041-, 0.053-, 0.061-, and even 0.071-inch com­pressed thick­nesses.04



[ Jeff Smith fixed the sick 469ci short-block. This month, he deals with pis­ton deck clear­ance, val­ve­train, oil pan, and drive­abil­ity is­sues.

[ The Rat that roared: Af­ter Smith threw a curve in the dis­trib­u­tor, Sch­miege hit the road and drove straight home to San Diego.

[ Milodon’s ex­tra-low-pro­file oil pan, high­vol­ume oil pump, and match­ing pickup and screen re­solved the Bel Air’s oil pan is­sues.

12–14] “The ex­ist­ing non-ARP rear main cap stud was too long,” Smith says. “I had to cut it down and use a spare 12-point nut to clear the Milodon high-vol­ume pump’s thicker cast­ing” ( 12). ARP sells in­di­vid­ual 180,000-psi 12-point nuts if you need one. Use ARP Ul­tra-Torque on the threads and be­tween the nut or bolt head and washer top (never the washer bot­tom). Fel-Pro brings modern seal­ing tech to the 1965–1990 Mark IV Rats with its one-piece, 0.094-inch-thick oil pan gas­ket made from molded rub­ber with a rigid car­rier ( 13). Mea­sur­ing off the pan rail with gas­ket in place, sub­tract the oil pump screen dis­tance from the pan sump depth ( 14). “I like to see 3⁄ inch from the8 screen to the bot­tom of the pan,” Smith says. “Ours was closer to ½ inch—close enough be­cause Sch­miege isn’t go­ing rac­ing.”

11] Milodon’s en­gine-plug set in­cludes all those hard-to-find en­gine cup and screw-in plugs. The freeze plugs are cor­ro­sion-re­sis­tant brass. The old-school Chevy orange paint is by Du­pliColor. Two FRAM tough-guard oil fil­ters were ex­pended: one for ini­tial run-in, one for af­ter. Lu­cas sup­plied the high-ZDDP mo­tor oil.

The cen­trifu­gal ad­vance curve did need some re­work. With the ex­ist­ing soft “ball­point pen” light-blue springs, Smith says the “ad­vance curve was all in by 1,100 rpm! It wouldn’t idle un­der 1,100 rpm at any­thing less than 25 de­grees ini­tial, even with the vac­uum ad­vance dis­con­nected.” Re­plac­ing one of the light springs with a heavy sil­ver “garage-door” spring was the cure. 17]

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