Substituting a Modern Delco Alternator for that old AMC/Rambler Motorola

Written by Tom Jennings, edited by Frank Swygert 02-23-2026

There’s nothing wrong with the older Motorola alternators, other than they’re all old and are expensive to replace. The Delco alternator used by Chevrolet is common as dirt, half (or less) the cost, have twice the output, a built-in voltage regulator, and one minor problem: the case is a bit bigger than the smaller Motorola.

Frank: Tom is talking mainly about Delco 10SI and 12SI models. The 10SI was used by GM from 1973-1987 in 37, 42, 55, 61 and 63 amp ratings. The 12SI was used 1983-88 and is the same physical size, but has an increased cooling capacity and comes in 56, 66, 78 and 94 amp ratings. These have been cloned and are readily available today. The 10SI is usually found to be the cheapest replacement alternator available. The clones appear to be just as good as rebuilt originals, so don’t worry about not seeing “Delco-Remy” cast into the case.

You can buy a new universal alternator/generator bracket bracket from a speed shop (https://www.steinertractor.com/ABC404-Universal-Alternator-Mounting-Kit), or you can hack up the existing Motorola alternator mounting bracket to accommodate the wider mount base Delco. The photos below show how I simply drilled out the spot-welds to split the two bracket halves, re-drilled it for the right width, and stuck it back on. It ain’t rocket science. Or you can file off the Delco housing aluminum to fit (I can’t bring myself to do things like that) or find a compatible “one-wire” alt from a foreign car, or there may be Delcos of smaller diameter.

Frank: It’s easy to see that the original early 60s bracket is simply two pieces of bar stock with 90 degree bends on the end. It’s easy to buy a 12″ length of 1/2″ wide x 1/8″ thick bar stock and make a bracket.

The problem is that the Delco is big and there is barely enough room for it; it wants to interfere with the block in one direction, and the steering gear in the other. With manual steering it just fits as-is. With power steering there’s not enough room to adjust the V-belt. Matt Hass worked out which fan belt will make it fit (36″ Dayco 15360 or equivalent for 64-74 AMC 199/232/258 sixes, which is 1/2″ shorter than the original Motorola alternator belt — see https://www.mattsoldcars.com/RestoreAmerican/delco10si.shtml for how Matt did it).