Eric Schmiege’s Rat Ate a Nut. We Cured the Sick Short-Block, but Top End, Oil Pan, and Driveability Issues Still Need Fixing.
THE RESCUE SO FAR
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.
THE FIX: DECK HEIGHT
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.
THE FIX: VALVETRAIN
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.”
THE FIX: OIL PAN
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.
THE FIX: TUNE-UP
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]