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Corvette Distributor Rebuild - Rebuilding The Tach-Drive DistributorRestoring Performance In A Delco-Remy Window Cap Distributor From the January, 2010 issue of Corvette Fever By Moses Ludel Photography by Moses Ludel
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Delco-Remy's window cap distributor... Delco-Remy's window cap distributor was an engineering breakthrough. A unique breaker point design allows point adjustment through the cap's window. This can be done with the engine running, a timesaving, fine tuning approach. Another innovation of the window cap distributor is its spring hook hold-downs. The postwar General Motors OHV V-8s were difficult to tune. Ignition distributors mounted at the firewall end of the engine, and the breaker points and condenser were difficult to replace. In the late '40s and 1950s, professionals turned to distributor strobe machines and worked on the ignition with the distributor removed from the engine. As a solution to these tuning difficulties, the '56 Cadillac introduced Delco-Remy's innovative "window cap" distributor. The newly designed ignition afforded ready access for breaker point adjustment. Dwell angle settings and point gap changes could be made with the cap in place and the engine running. This eliminated the cumbersome, repetitive removal of the distributor cap while performing a tune-up in the engine bay. Other G.M. divisions adopted the window cap distributor, and by 1958, only the dual four-barrel carbureted, dual-point Corvette engines retained a non-window cap distributor. This '57-'61 #1110891 application is smaller in diameter at the cap to permit installation of two WCFB carburetors. From 1958-'74, single-point Corvette distributors have window caps. (Most '58-'65 mechanically fuel-injected engines feature a unique, dual-point window cap distributor. Some later applications use a transistorized distributor.) The window in the distributor cap provides access to a set of redesigned points that use a horizontally positioned breaker-point adjuster screw. Window caps simplify and refine the tuning of breaker points. This Corvette #1111493 distributor... This Corvette #1111493 distributor shows years of wear and various aftermarket, non-OEM parts. The performance goal is to restore the reliability of the distributor. To enhance the car's value, this 350 horsepower, 350 V-8's ignition will also receive authentic detailing. The distributor has wobbly bushings and general wear. Breaker point Delco-Remy distributors were well crafted and durable. Engineering innovations, like a window cap distributor, were aimed at ease of service. In addition to the window cap, the breaker points have a pivoting feature that enables external adjustment of the point gap. Using a dwell meter, the point gap is set without needing to remove the distributor cap several times. These point sets can be adjusted with the engine running! Unknown to many tuners, the window cap distributor's breaker points can often be adjusted without a dwell meter. In the earlier service data, one approach called for adjusting the points roughly, enough to start the engine. Gap the points with a feeler gauge or by eye then install the cap. Start the engine. With an Allen (hex) wrench inserted into the adjuster screw, turn the screw clockwise until the engine begins to misfire. Back the screw out 180 degrees. This brings dwell within specification in most cases. Trackside, this fast breaker point adjusting method proved a boon. It also works nicely when the points fail while cruising through a deserted neighborhood at night. If you carry an extra set in your road kit, you can install points and adjust them with nothing more than an Allen wrench. You can confirm dwell with a meter once your Corvette is back in a secure environment-with access to more tools. Rotor removed, the centrifugal... Rotor removed, the centrifugal advance mechanism is visible. Congealed and crusty grease prevents weights from moving freely. Spring length and tension determine the rpm at which spark advance occurs. The weight movement swings the distributor cam in the advance direction. A limiter bushing (below the drive flange) sets the total degrees of advance. Traditionally, these point sets were packaged with the points preset, often close enough to start the engine. Slots at each end of the point set allow easy installation of the points without removing either hold-down screw. The starting gap is approximately 0.016 inch, which can be eyeballed if a feeler gauge is not available. As soon as the engine starts, adjust the points with a dwell meter or use the "turn-in-to-roughness then back out 180-degrees" technique. Accurate dwell angle must be set with a dwell meter. Tuning must be performed each 12,000-15,000 miles, even with the long life point sets available. Some owners opt for installing an electronic breakerless conversion, and this is not difficult with the kits available. The choice is simply owner preference. Most kits permit restoring the distributor to stock if necessary. Tach-Drive Distributor Rebuild
At higher mileage, a C-1 through 1974 window cap distributor likely needs rebuilding. For restoration or rebuilding purposes, a tachometer drive distributor has some additional wear points. The distributor illustrated is distinguishable by its iron housing and no drive for the fuel injection. The 1111493 distributor tag number indicates a '69-'70 350 horsepower 350 V-8 application. This design is typical of '62-'74 non-transistorized, non-fuel injection units. Tach drive coupler is a softer... Tach drive coupler is a softer bronze material. When removing the drive gear, loosen the coupler with a suitable driver. This tool can be fabricated from sheetmetal thick enough to fill the cross slots snugly. Create a notch to clear the drive gear. While loosening or tightening the coupler, hold the tool steadily to prevent damage to the slots. A fluctuating dwell angle reading is the first clue that a distributor needs rebuilding. If the distributor shaft bushings have wear in excess of two degrees variation on the meter, the distributor needs a complete rebuild. Shaft and bushing play can be tested with the distributor still in the engine. Remove the cap and check the movement of the shaft. If a dial indicator is not available, insert a feeler gauge into the point gap with the rubbing block on the high point of the cam lobe. Pull and push the shaft toward and away from the rubbing block. Note the amount of change in the point gap. Excess movement is a clear sign of bushing wear. If in doubt, remove and disassemble the distributor. Often, after cleaning away varnish and debris, the shaft play will be even greater. If a rebuild is necessary, mark the location of the distributor base and the intake manifold. Cap removed, index the rotor by placing the crankshaft damper at the TDC mark for #1 cylinder. Mark the distributor housing where the rotor points toward #1 spark lead. This will enable easier installation of the distributor and provide a firing position for starting the engine. Once the engine starts, you can verify timing with a light, following the procedure in your factory workshop manual. Carefully remove the tach... Carefully remove the tach drive coupler and drive gear. Remove the distributor drive gear's pin and the drive gear. Slide the driveshaft out and remove the spring or wave clip that retains the point breaker plate. Measure the height of the upper bushing above the housing bore. Using a suitable bushing driver with an arbor press, carefully remove the two bronze bushings from the housing. Though not complicated, distributor rebuilding requires care, detail, and cleanliness. The distributor's driveshaft spins the oil pump, which must function flawlessly. Debris that falls into the engine can contaminate the crankcase. If abrasive, debris can circulate and cause internal parts damage. Use a shop vacuum around the distributor's base and the intake manifold before removing or installing the distributor. Cover the distributor opening with a clean rag to prevent debris or hardware from dropping into the engine when the distributor is out. The ignition distributor, including its advance mechanisms, plays a crucial role in the performance and reliability of a Corvette engine. Adequate spark and timing accuracy determine the ease of startups, acceleration, cruise performance and passing power. When wear exceeds simple tune-up needs like new spark plugs, points, condenser, rotor and cap, a distributor rebuild can restore power and provide years of reliable service.
| Difficulty Index - 3 Wrenches |
| Anyone’s Project: no tools required | 1 Wrench |
| Beginner: basic tools | 2 Wrenches |
| Experienced: special tools | 3 Wrenches |
| Accomplished: special tools and outside help | 4 Wrenches |
| Professionals Only: send this work out | 5 Wrenches |  Upper bushing and its grease...  Upper bushing and its grease cavity show wear and solidified grease. Bushings are durable and need no attention over the distributor's service life. Use of proper greases during assembly will preserve the breaker plate and upper bushing. Align the upper bushing's oil hole and the tach drive gear's notch when fitting the new bushings.  Wear points in these distributors...  Wear points in these distributors are clear. Fortunately, the points, condenser, rotor, breaker plate, driveshaft, shaft bushings, weights and springs, the drive gear, vacuum advance and hardware are still available for this distributor. The tach drive parts are also vulnerable to wear, with parts available in the aftermarket.  Parts like this breaker plate...  Parts like this breaker plate have bearing surfaces and electrical wiring. The bushing on this plate has no appreciable wear. The wire is a ground and shows slight oxidation and corrosion. The corrosion can be eliminated with a quality contact cleaner or baking soda rinse. Driveshafts seldom wear out; however, a replacement shaft is currently available if needed.  Unless the distributor cam...  Unless the distributor cam lobes have bad wear or scratches, the surface can be restored with a polishing buffer and metal polish. This cam must be smooth, or the breaker point's rubbing block will deteriorate quickly, closing the point gap. Take time to restore shafts and running surfaces.  The cam assembly looks like...  The cam assembly looks like new after polishing and cleaning. Hard parts need abrasive cleaning with appropriate soda or glass bead blasting. The breaker plate can be re-plated if necessary, using a zinc electroplating system like the one available from Eastwood Company. Apply these restoration procedures if new parts are not available.  These crucial parts are now...  These crucial parts are now restored. Cost of NOS parts can be high, depending upon demand. By restoring the housing, breaker plate, and cam assembly to perform as new, this Corvette distributor remains authentic and ready for another four decades of service. OEM and NOS parts assure the quality that Delco-Remy built into these components.  Before disassembly, the height...  Before disassembly, the height of the old bushing was measured and noted. This new bushing must match the height of the original. If undersize, bushings should be reamed carefully. Once reamed nearly to size, bushings should be finished and burnished to match the shaft diameter. A drill motor, an old driveshaft, and lapping compound work well for this task. Metal polish can create a polished, final finish. Thoroughly clean away any abrasive.  Use an arbor press and proper...  Use an arbor press and proper diameter bushing drivers to prevent peening edges. Apply an anti-galling lubricant when pressing parts together. Size and burnish the bushings to fit. To maintain bore alignment of these two bushings, use a long reamer or polishing shaft to size both bushings at the same time.  Bushing positioned properly...  Bushing positioned properly and polished in alignment with the lower bushing, this distributor is ready for assembly. Cleaned in a parts washing cabinet, glass beaded and then washed again, the housing looks new. Iron is strong and durable. Later distributors shifted to aluminum housings, which require careful handling and mild abrasive cleaning.  Appropriate masking, primer,...  Appropriate masking, primer, and paint will restore the housing to new appearance. Use a suitable engine-grade primer and paint. This Dupli-Color engine enamel covers well, has excellent adhesion on freshly scoured iron, and contains ceramic for heat resistance. Eastwood and others also offer products for these tasks.  This array of parts represents...  This array of parts represents a true restoration. NOS centrifugal weights, a new driveshaft, drive gear, small parts, Echlin premium tune-up parts, a new primary wire and grommet, plus new shaft bushings create a like-new distributor! Points, condenser, rotor, and cap are routinely replaced.  Assembly is the reverse of...  Assembly is the reverse of disassembly. A felt pad and grease retainer help lubricate the breaker plate. The plate pivots on the upper housing bushing. Make sure that the retaining wave washer and nylon grease seal are properly in place. Bosch grease for breaker point rubbing blocks works very well in this grease cavity.  When rebuilding a distributor...  When rebuilding a distributor thoroughly, you will want to replace the vacuum advance unit. These calibrated vacuum canisters must match the factory rated pull. If you cannot find a canister match, based upon the distributor tag number, there are universal, adjustable canisters available from Mr. Gasket and others.  This is a strobe check of...  This is a strobe check of the vacuum and centrifugal advance mechanisms. Vacuum advance works at throttle tip-in and light throttle. The centrifugal advance weights and springs, located beneath the rotor, determine the rpm and degrees of total mechanical advance. Centrifugal advance responds solely to engine speed.  Wires must be clear of moving...  Wires must be clear of moving parts and able to move without chafing or wear over time. Keep wires well below the spinning rotor. Route wires away from metal edges. Lube the point rubbing block and oil wick with a grease like Bosch #5700 002 005. Apply grease as noted in the point set instructions.  Insert the tach drive gear's...  Insert the tach drive gear's button if removed during service. Grease the tach drive gear and cavity. Use a new sealing washer at the base of the bronze coupling. Secure the coupling and spin the distributor shaft. The shaft drive gear uses a thrust washer(s) that must be installed between the gear and distributor housing base. Use a new pin to secure the gear.  Insert the tach drive gear's...  Insert the tach drive gear's button if removed during service. Grease the tach drive gear and cavity. Use a new sealing washer at the base of the bronze coupling. Secure the coupling and spin the distributor shaft. The shaft drive gear uses a thrust washer(s) that must be installed between the gear and distributor housing base. Use a new pin to secure the gear.  This is the restored and run-ready...  This is the restored and run-ready #1111493 Delco-Remy distributor unit. The factory tag is on the collar of the housing, signifying the application (350 horsepower, 350 V-8). If you want a matching numbers restoration, this is it! Remove the cap to index the rotor position during installation in the engine.
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