The first step in replacing...
The first step in replacing our Firebird's starter motor is removing the ground cable from the battery post.
Oftentimes, the battery can at first overcome this resistance and sufficiently crank the engine with little indication of a pending problem. The added resistance places a great load on the battery, however, and will cause the starter motor to crank slowly or in extreme cases, not at all. Many owners then replace the battery, falsely assuming it isn't functioning properly, but the situation primarily lies within the starter.
Our Pontiac
The original 400 in our '67 Firebird convertible was in clear need of a complete rebuild. Since additional performance was a goal, we opted to save the numbers-matching block and drop a mildly-modified 455 between its framerails. While performing the swap, we noticed that the Firebird's original starter motor had somewhat recently been replaced with a remanufactured Delco unit and it seemed as if it was in good working order.
Though not optimal for maximum performance, the Firebird's existing exhaust system was in reasonably good shape and included uncoated tubular headers. We elected to retain the entire system to not risk damaging a new, ceramic-coated header set during flat-tappet camshaft break-in. It wasn't long after initial break-in that the stock Delco starter motor began dragging on hot restart, however. We knew that starter replacement was inevitable, so we began searching for a compact gear-reduction unit.
After taking out the stamped-steel...
After taking out the stamped-steel inspection cover, we removed the two long bolts securing the starter to the block using a 9/16-inch socket. (There most likely are starter shims between it and the block. Save them for possible reuse during reassembly.) We were fortunate in that we didn't have to loosen the header to extract the starter. That's usually not the case!
IMI Performance Products
Hi-Torque IMI Performance Products (IMI) in Whittier, California, is one company that offers gear-reduction starters for a wide array of vintage applications. "Pontiacs seem to experience 'hot start' conditions more often than other makes," says Jack Isom, a Senior Technician for the company. "I believe it's caused by the starter's mounting location and the Delco starter's steel casing. Our Pontiac V-8 starter was introduced in 1996 and we've had great success with it."
IMI's Hi-Torque starters are created using an American-made OEM Denso unit. In addition to its high-speed electric motor, its solenoid is encased in aluminum, which dissipates heat quicker than steel and also includes a vent tube to increase overall airflow. Featuring a 4.44:1 ratio through gear-ratio reduction, IMI's base unit is rated at 1.2 Kilowatts (Kw)-a typical 1:1 Delco starter is rated at 1.0. IMI offers units with ratings as high as 2.0 Kw for specific applications.
Isom asked us to describe our Pontiac to him, specifically including its engine size, modifications, and intended use. After explaining that the powerplant is only mildly modified and that the vehicle's primary use is street cruising, he suggested his company's 1.4 Kw unit for our application (No. IMI-108N). Cost for our particular one was $225 plus shipping, and it was on our doorstep in days.
Installation was very straightforward, and the supplied instructions provided all the necessary details to properly measure clearances. The task took little more than an hour to complete, and its effects were immediately noticeable. Our 455 was cranking over more forcefully than ever before, and the starter motor seemed unaffected by temperature, no matter how long it sat after being driven.
Conclusion
Whether it's a street-driven cruiser with tubular headers or stock-appearing racer fitted with high-flow cast-iron exhaust manifolds, starter drag on hot-restart is a common malady many Pontiac hobbyists share. While there are a number of solutions to remedy the situation, the simplest and most reliable may be a mild injection of modern technology that's affordable and installs easily. You can rest assured that the high-pitch whine associated with a gear-reduction starter will be music to your ears for years to come!
To prevent damaging the starter's...
To prevent damaging the starter's delicate wiring, we supported the housing from beneath and let it down only far enough to fully access the solenoid terminals. We will remove the large red wire to the battery's positive terminal with a 5/8-inch wrench and use an 11/32-inch wrench to remove the smaller orange wire, which runs to the ignition switch. Then we'll employ a 3/8-16 tap to clean the block's threads.
It's obvious just how much...
It's obvious just how much larger the original Delco unit is when compared to IMI's replacement. In addition to its increased output, the gear-reduction unit features an aluminum housing, which improves heat dissipation and reduces weight. The compact unit weighs just 9.5 pounds. The Delco unit, with its cast-iron casing, checks in at 20 pounds.
The IMI starter allows us...
The IMI starter allows us to rotate the motor and solenoid assembly to six different positions 20 degrees apart to maximize clearance. We found ours was optimally positioned for our particular combination out of the box.