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EZ-EFI Issues on 1967 Corvette Traced to Bad Valve Seals

The 350 in Bill Hedekin's 1967 Corvette Backfires, Stalls, and Uses Oil

Marlan Davis Jun 22, 2017
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01B 1967 Corvette Bill And Linda Hedekin 660x440 2/57

Bill and Linda Hedekin bought their vintage 1967 Corvette in the late 1970s. The exroad racer has long since been returned to the street.

The Combo

Bill Hedekin's 1967 Corvette should have been a runner. Once a late-1960s-style SCCA B/Production road racer, the car was returned to street duty, still equipped with a vintage 355ci Mouse with fuelie heads and vintage Edelbrock Torker single-plane intake—but upgraded and rebuilt with Total Seal piston rings, a modern Comp Cams Magnum 280HR hydraulic roller cam, an MSD-6AL ignition, and a FAST EZ-EFI self-tuning, throttle-body fuel injection. Power is transferred back through an M21 Muncie close-ratio, four-speed manual trans to a 3.73:1 Posi IRS.

02A 1967 Corvette Static 660x440 3/57

The vintage small-bock was rebuilt a few years ago with a big hydraulic roller cam and EZ-EFI. It had poor driveability and burned oil.

The Problem

After the engine refresh, "The car never seemed to be right," Hedekin says. "It popped and banged whenever I backed off the gas, like a backfire from an old-fashioned carburetor. It always starts fine, but cuts out under throttle. There's always oil on the [spark] plugs. I've changed the plugs myself three or four times, even tried specialty plugs. Several shops tried to tune it. Nothing really helped." In his rescue request interview, Hedekin primarily blamed the EFI, mentioning the oil-fouled plugs only in passing. When pressed, he allowed, "The car does burn some oil—probably 1 quart every 100 miles."

The Diagnosis

04 Norm Rollings 660x440 4/57

One of a vanishing breed of full-service auto-repair shops, Norm Rollings can fix anything—early to late, stocker to race car.

We sent the Diamond Bar, Californiabased car to Rollings Automotive, a full-service shop in Mira Loma, California. Owner Norm Rollings immediately homed in on the oil consumption—not the EFI—as the primary stumbling block. Explains Rollings, "You don't lose that much oil unless there's something physically wrong. EFI won't work right with an oil-use problem. Oil attacks the O2 sensor, which messes up everything, including the system's self-tuning ability. We needed to find out where the oil was coming from.

"The first step was to look at engine vacuum. A vacuum leak can suck oil into the [intake] manifold runners, from a poor manifold-to-head intake-surface seal or even the wrong intake gasket. That can be tough to find because it can be sucking in from the bottom (the valley side, underneath the manifold). But vacuum was still about 15 inches, even though a vacuum hose had fallen off.

"The disconnected hose did cause the fuel pressure regulator to go to maximum pressure at idle, which will contribute to the driveability issues, but sticking the hose back on produced no significant change in vacuum or driveability for the moment."

07 Vacuum Hose Disconnected 660x440 5/57

Vacuum was an acceptable 15 inches, even though a hose had fallen off the throttle-body. The hose's other end connects to the fuel pressure regulator, but hooking it back up didn't initially improve driveability.

"We then pulled the [spark] plugs. They were really contaminated with oil. We did a leakdown and compression test. The cylinders had good compression and only 8- to 10-percent leakage, which is about ballpark for Total Seal rings on a street car, so it probably wasn't the rings or valve seats."

08 Oil Fouled Spark Plugs 660x440 6/57

Engine compression and leakdown test readings were normal, but the spark plugs were oil-fouled.

"Next we pulled the valve covers to check the valve-guide slop on the engine's rare camel-hump factory heads. To measure this, we had to pull the valvesprings. In the process, we found a broken inner damper. This made us question the integrity of all the springs."

09 Z28 Valvespring Broken Damper 660x440 7/57

Several valvesprings had broken dampers.

Hedekin says the springs were "an old Z28 design that fit the stock valvespring pocket." Z28 springs were designed for the old lazy stock solid lifter cams and they don't really have enough pressure to support today's hydraulic roller cams.

Springs removed, Rollings observed, "The heads still had old OE umbrella valve seals. Today we machine the guides for positive-stop seals. They offer better oil control in all cases, but with Hedekin's high-lift cam, positive-stop seals are mandatory: The big lift was crushing the seals into the top of the valveguide; we could visually see there was contact. The old seals could only support around 0.470 lift, but Hedekin's cam had 0.525 lift. But at least the heads' bronze valve guides were still nice and tight. So in terms of oil consumption, the only problem was retainer-to-seal interference. The crushed seals let oil run right down the guides. Engine vacuum sucked oil down the valve stem into the engine."

03 Umbrella Valve Seals 660x440 8/57

High oil use was traced to umbrella-type valve seals getting crushed by the spring retainers. The seals were too tall for a 0.525-inch-lift cam.

The minimalist (and more affordable) approach is modifying the existing heads to accept modern springs and positive-stopstyle valve seals. The Daddy Warbucks method is a top-end swap to modern aftermarket aluminum heads. We'll show you both ways to go.

The Fix: Existing Heads

12 Comp Cams Valve Guide Cutter 4726 And Arbor 4732 Callouts 660x440 9/57

To install positive-stop valve seals, remove and disassemble the heads, then machine the top of the guide with a special cutter and arbor. The cutter (A) must match the guide od and the arbor (pilot, B) the valve-stem od. These old Chevy heads had 0.530-inch-od guides and stock 1132-inch valve stems. Comp Cams sells the correct cutter under PN 4726 and the arbor under PN 4732.

13A Use Drill To Mod Guides For PC Seal 660x994 10/57

The guides can be cut at home using a common hand drill. Rollings usually places a thick valvespring seat insert in the pocket to protect the guide during the machining process, then cuts the "chimney" portion of the stock guide down about 0.200 inch to where it widens out.

"Original positive-stop or 'PC seals' were made from Teflon," Rollings explains. "They're OK for the race engines they were originally developed for, but today's street motors don't like a pure Teflon-based seal. They're not malleable enough to conform to the valve stem and can also wear the stem where the seal's 'cylinder' rides. Instead we use a Viton-based seal, with a spring around it for radial tension. It doesn't harden, and it's not affected by heat-cycling. It wipes oil off the stem like a windshield-wiper blade wipes water off the windshield." Modifying the valve guides for positive-stop seals is easily done at home with a hand drill and the appropriate arbor and cutter tooling available through Comp Cams.

14 Positive Stop Seal Guide Machined 660x440 11/57

Here, the right-hand guide pair is still unmachined. The bronze wall guides' "chimney" still sticks up out of the guide casting. On the finished left-hand pair, the guide has been lowered about 0.200 inch and its major diameter decreased. The chimney is now flush with the top of the guide.

15 Machined Guide Now Has Plenty Of Clearance 660x994 12/57

The cut-down guides provide up to 0.881-inch clearance between the bottom of the retainer and the top of the guide. Subtracting 0.100-inch to allow for the new seal height plus a 0.060-inch safety margin in case of valve float, still leaves sufficient clearance for a 0.721-inch-lift cam. (Hedekin's cam has 0.525-inch lift with his existing 1.5:1 Comp Pro-Magnum roller rockers.)

The valvespring issue was harder to resolve. Back in the day, the usual approach was machining the spring pockets oversize to accept double (or even triple) springs. But this doesn't always work for all heads. Hedekin had No. 492 castings; those made before 1972 have thin spring pockets and machining them with a traditional flat seat cutter may break through into the water jacket. Special stepped cutters are available, but Rollings says they're not compatible with his preferred modern, hydraulic-roller-cam-compatible spring designs. In any event, there was also insufficient material between the outer pockets and head-bolt holes on each end of the head to adequately support larger springs.

16 461 Head Machined For Big Spring ARROW 660x440 13/57

This is a classic small-block No. 461 early camel-hump "fuelie" head. Its stock 1.290-inch spring seats have been cut oversize for these 1.430-inch-od triple race springs—yet there's still enough material (arrows) between the pocket's outer edge and the head bolt/stud hole at the end of the head to support the wider spring; the casting material does not have a steep drop off.

17 Chevy 492 Head No Material To Accept Big Spring ARROW 660x440 14/57

This is Hedekin's later No. 492 head with the conical spring and positive-stop seal installed in the stock 1.290-inch seat. This casting lacks sufficient material (arrow) between the pocket's outer edge and the head bolt hole at the end of the head to support a large-diameter pocket; the casting wall "drops off a cliff," which would leave a larger-diameter spring "hanging in the wind."

What was needed was a spring and retainer that fit the stock pocket while developing adequate pressure for the hydraulic roller cam. Enter a Comp Cams conical spring and retainer combo originally developed for today's LS engines with their small spring pockets and 8mm valve stems. Conical springs increase the valvetrain rpm limit, reduce resonance, and decrease dynamic spring oscillations. The result: longer spring life and the ability to run more aggressive cams. Comp offers a hybrid 7-degree lock that allows installing this spring and retainer on an old small-block's 11/32-inch valve stems. On paper, the conicals are designed to generate the desired seat and open pressures at the usual small-block 1.800-inch installed height.

As it turns out, the new springs' retainers are effectively thicker than the retainers used with conventional springs; with no other changes, the installed height ends up about 0.100-inch shorter, considerably raising spring pressures (table). Even so, Comp Cams' Valvetrain Group Manager Billy Godbold maintains these higher than "normal" pressures are still OK with a hydraulic roller. With Hedekin's 0.525-inch-lift cam, there's still 0.050 inch remaining until coil bind. That's a little tight according to old-school theory, but again, Godbold isn't worried: "Due the conical spring's unique design, it actually likes and performs best when installed close to coil-bind."

18 Concial Spring Retainer Thickness 660x440 15/57

The distance on the smaller-od (but thicker in height) conical spring retainer is actually greater from the valve locks to the spring-to-retainer lip contact point than it is with a conventional retainer. With no other changes, the conical's 1.700-inch installed height (right) ends up at 1.700 inch, 0.100-inch shorter compared to a "standard" spring and retainer (left) installed in the existing pocket at 1.800 inch.

If (as is the case on 492 heads) the pocket can't be deepened and you're uncomfortable with a shorter installed height, don't want such high seat pressures, and/or have an even higher-lift cam, the first step is offset valve locks, which offer about 0.050 inch more clearance. The next step is 0.100-inch longer-than-stock valves. On a small-block Chevy, "plus-0.100" valves require about 0.100-inch longer pushrods to restore proper valvetrain geometry—assuming the existing pushrod lengths were correct in the first place. The cam's base circle diameter, lifter height, head-gasket thickness, and the amount the block and heads were milled also influence pushrod length. Rollings recommends mocking up the motor and using a Manley pushrod checker to positively determine the proper length.

19 492 Head Long Valves Conical Spring Positive Stop Seal 660x440 16/57

To compensate for the thicker retainers, Rollings installed 0.100-inch longer-than-stock SI stainless steel valves. Use at least a 0.015-inch shim to prevent seat erosion from the valvespring's harder chrome-moly steel. Here, you can see the Comp conical springs, positive-stop seals fully installed, new valves, and shims in the process of assembly.

The Fix: Edelbrock Heads

20 Edelbrock Small Block Chevy Performer RPM Head 60895 Angled 660x440 17/57

In the end, owner Hedekin thought it was an opportune time to upgrade to a set of modern, free-flowing Edelbrock Performer RPM heads. They deliver great throttle response and power from 1,5006,500 rpm, shed front-end weight, and come in several bare and fully assembled variations for compatibility with modern cams and unleaded fuel.(Photo: Edelbrock LLC)

22 Fel Pro Head Gasket 1003 660x440 18/57

The same Fel-Pro Performance-series head gasket (PN 1003, shown), intake set, and valve-cover gasket work on both the old GM and the new Edelbrock heads. The head gasket features a flattened stainless steel fire ring that minimizes aluminum head brinelling while providing optimum sealing. Use a thread-chaser tap to clean out the old corroded head-bolt holes.

The other solution—and the one Hedekin self-selected—was swapping on modern Edelbrock Performer RPM heads. Perfect for street performance, daily drivers, street rods, and muscle cars, the specific version installed on the Vette (PN 60895) has 64cc combustion chambers and straight spark-plug holes, and comes fully assembled with hydraulic-roller-cam-compatible springs. They bolted right on to the Vette's existing short-block. The only glitch was due to the new heads' slightly taller valve-cover rails: One of Hedekin's existing Chevrolet Performance bow-tie valve covers had to be notched at the rear driver-side to clear the Vette's power-brake vacuum booster. Hedekin also had Rollings replace his old Torker intake with an Edelbrock Air-Gap dual-plane unit (PN 7501).

24 Valve Cover Notched For Booster Clearance 660x440 19/57

On the driver side, the Edelbrock heads' taller valve-cover rails caused the rear outer corner on the owner's existing Chevrolet Performance bow-tie valve cover to hit the power-brake vacuum booster. Michael Cox Racing Development notched and reshaped the cast-aluminum cover for clearance, then Rollings retouched it with VHT black-wrinkle paint.

23 ARP Head Bolt Kit 134 3601 660x440 20/57

Rollings trash-canned the old corroded head bolts. ARP's High Performanceseries small-block Chevy bolt kit (PN 134-3601) fits the OE iron as well as Edelbrock Performer RPM heads. Since the bolts go into the water jacket, be sure to put a Teflon-based sealant on the threads to prevent weeping.

The Fix: EZ-EFI

25 Weird Fuel Pressure Reading Low ARROWS 660x440 21/57

Engine buttoned up, Rollings addressed the EFI: "We checked the fuel pressure. It was roughly 38 psi when it should have been 50. Whenever we accelerated, the fuel pressure went down to 30 psi or less. It should have gone up along with rpm. This was even with the now-reconnected vacuum hose (arrows), so we knew we had either a fuel-pump or fuel-filter problem."

10AB Debris Plugging Screen Style Fuel Filter 660x440 22/57

Rollings discovered debris plugging the Vette's rear-mounted, screen-style fuel filter.

Oil consumption solved and new heads installed, the EZ-EFI was cleared and put into self-tune mode. Idle and part-throttle after warm-up quickly normalized. However, accelerating hard, the engine shut off under load. The fuel pressure was actually declining as rpm rose, when it should have gone up. This indicates either a fuel-pump or fuel-filter problem. Rollings found a clogged fine-mesh screen in a fuel filter poorly located between the fuel tank and fuel pump. As there already was a larger fuel filter installed after the pump, Rollings simply removed the redundant screen filter, then set the fuel pressure regulator to 55 psi. Fuel pressure issue rectified, the only additional manual tweak needed was dialing in a little more cold-start enrichment.

26 Remove Fuel Filter Between Tank And Pump ARROWS 660x440 23/57

The Vette had a fuel filter (A) installed between the tank and pump. Rollings says, "I don't like a filter in that location because it can pull vacuum, but in this case, it was even worse: Inside the filter there was a 1-inch disk with a fine-mesh screen that was plugged up with debris." There's another filter (B) after the pump—as there should be—so Rollings removed the upstream filter.

27 EZ EFI Tuner Screen 660x440 24/57

"Once we set all the basic adjustments on the supplied handheld tuner," Rollings explains, "the system was able to do its own tuning, and the car now runs fine. We did have to manually supply 'more choke' at cold start-up by turning the cold-start enrichment screen on the handheld tuner up a couple of clicks."

Lessons Learned

Don't just bolt things together. You must be sure the valvespring is compatible with the cam, the retainer-to-valve guide and valve-seal clearance is right, and the spring's installed height develops the recommended pressures without going into coil bind. Don't use a fine-screen filter between the fuel tank and fuel pump. Make sure the engine internals, the electrical system, and the fuel-supply system are up to snuff before casting blame on the fuel injection.

28 1967 Corvette Hedekin Engine Bay After Rescue 660x440 25/57

New life for an old Corvette: Rescue complete, the classic Vette's engine bay proudly shows the new Edelbrock heads, the Air-Gap intake that replaced his ancient Torker, and the now-perfected EZ-EFI system. Hedekin's next goal: Install a newfangled electric air-conditioning system.

05 Comp Conical Spring And Positive Stop Seal On GM 492 Head 660x440 26/57

The old GM heads were machined for positive-stop seals, then upgraded with Comp Cams conical springs and 0.100-inch-longer SI valves.

06A 1967 Corvette Motion 660x440 27/57

After resolving the mechanical issues, sorting out the EZ-EFI was easy. Now the Hedekins can handle those mountain twistys in style.

11 Cleaning Off Carbon Deposits Cropped 660x440 28/57

There was so much oil in the motor, the pistons and cylinder head combustion chambers had a ton of carbon buildup. Rollings explains, "Carbon particles glow at high temperature, which can promote preignition when fuel is introduced. We removed them using Scotch-Brite, gasket scrapers, carb cleaner, and lots of elbow grease."

21 Small Block Chevy Use Silicone On Head Deck Intake Corner__20160812_120531 660x440 29/57

Rollings applies a little silicone sealant in the last inch of the trough area between the intake manifold corners and the head-gasket surface to prevent weeping. The "dimples" on the block China wall show you just how old the vintage block was; it was an old-school end-gasket sealing trick before silicone became available.

Contacts:

Accel, a Holley Performance Brand; Bowling Green, KY; 866.464.6553; Holley.com/brands/accel/

Automotive Racing Products (ARP); Ventura, CA; 800.826.3045 or 805.339.2200; ARP-Bolts.com

Champion—Fel-Pro (Federal-Mogul Corp.); Southfield, MI; 800.325.8886; ChampionAutoParts.com, FelPro-Only.com, or FMe-cat.com

Comp Cams; Memphis, TN; 800.999.0853 or 901.795.2400; CompCams.com

Dura-Bond Bearing Co.; Carson City, NV; 775.883.8998; Dura-BondBearing.com

Edelbrock LLC; Torrance, CA; 800.416.8628 (tech) or 310.781.7222 (general); Edelbrock.com

Gates Corp.; Denver, CO; 303.744.5651; Gates.com

Lucas Oil Products Inc.; Corona, CA; 800.342.2512 or 951.270.0154; LucasOil.com

Manley Performance Products Inc.; Lakewood, NJ; 800.526.1362 or 732.905.3366; ManleyPerformance.com

Michael Cox Racing Development; Jurupa Valley, CA; 714.376.6113; Mwc247@gmail.com

O'Reilly Auto Parts; Springfield, MO; 888.327.7153 or 417.829.5727; OReillyAuto.com

Prestone Products Corp.; Danbury, CT; 888.269.0750; Prestone.com

RockAuto LLC; Madison, WI; 866.ROCKAUTO or 608.661.1376; RockAuto.com

Rollings Automotive Inc.; Mira Loma, CA; 951.361.3001; Plus.Google.com/+RollingsAutomotiveIncMiraLoma

RPM—Ron's Precision Machine, Inc.; Santaquin, UT; 866.700.5877 or 801.754.5338; RpmRons.com

SI Valves; Simi Valley, CA; 800.564.8258 or 805.582.0085; SIvalves.com

Summit Racing Equipment; Akron, OH; 800.230.3030 (orders) or 330.630.0240 (tech); SummitRacing.com

VHT Paints, a Division of Dupli-Color, Inc., a Sherwin-Williams Co.; 800.247.3270; Cleveland, OH; VHTpaint.com

Wix Filters; Gastonia, NC; 704.869.3421 (customer service), 704.864.6748 (sales), or 800.949.6698 (USA, product information); WixFilters.com

NEED JUNK FIXED? If your car has a gremlin that just won't quit, you could be chosen for Hot Rod to the Rescue. Email us at pitstop@HotRod.com and put "Rescue" in the subject line. Include a description of your problem, your location, a photo of the car, and a daytime phone number.

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