It's A Cadillac, Jack
I recently found a '72 El Dorado 500-cube engine near where I live for $200. I also have an '87 SM465 tranny out of a delivery truck that I want to use in the custom junk-mobile I'm building, code-named "The Mad Crapper." While perusing Jp online (for pics of Bree), I read about the Whatchamawhoozit buildup, but you didn't mention anything about adapting your SM420 to the Cadillac 500 you originally put in there. I was wondering if you could enlighten me as to the feasibility of mating the SM465 to the 500-as in the bellhousing, flywheel, and so on. I can handle all the fabrication that is required, but I just need some tech info if you have any. I know you magazine folks lead glamorous, rock-star lives and you don't like wasting time reading long e-mails about obscure applications, but I would really appreciate a response. Thanks.
Dan Hesse
Via e-mail
I covered the conversion, but it was years ago. I'll set the groupies aside for a moment to run it down for you again.
First, that engine is a killer. You'll really like it. It's easiest to just stab a BOPC-pattern TH400 behind it, but here's what you'll need to do to mate an SM465 to it:
Fly Wheel: Since that era Cadillac never came with a manual tranny, you're gonna need a custom piece. Maximum Torque Specialists (760/247-2553, www.500cid.com) carries what you need, but it's not cheap. The company also has a ton of parts and pieces to swap a Caddy engine in vehicles that didn't come with one.
Pilot Bushing: This is the trickiest part. You can dismantle the engine and take the crankshaft to a machine shop to be drilled for a regular Chevy pilot bushing. However, most people don't want to crack the gaskets on a sealed engine. If not, you're going to need to measure the id of the crankshaft bore and have a custom bushing turned for you out of bronze. Then you're going to need to drill into the crank with a 51/48- or 31/44-inch drill bit so the pilot shaft of the tranny won't bottom out on the crank. The crank is tapered in so it's easy to center the drill. Or you could just lop off the tip of the tranny input shaft so it won't bottom. Also, since the custom pilot bushing will stick out farther from the crank, you're going to need to grind off some of the input splines (about 11/44-inch, if memory serves) so they don't bottom on the pilot bushing.
Clutch: Standard 11-inch Chevy 10-spline clutch of your choice
Bell Housing: The SM465 has a large bearing retainer bore of 5.125 inches, while the SM420 has a standard bearing retainer bore of 4.684 inches. If you're using the SM420, you can get a Lakewood bellhousing for a Buick (PN 15120) and it will bolt to the back of the Caddy engine (use a Buick because it has the starter on the passenger-side like the Caddy-Pontiac and Olds have starters on driver side). When I mated my SM465 to my '70 500, I used a stock aluminum Chevy 5.125-inch bore SM465 bellhousing from a Chevy pickup and got a PN 0061 TransDapt Performance (562/921-7515 www.trans-dapt.com) adapter to mate the BOPC bolt pattern to the Chevy pattern.
Novak Conversions (877/602-1500 www.novak-adapt.com) will also take your 4.684-inch bore bellhousing and bore it out to 5.00 inches and machine the transmission input bearing retainer down to 4.995 inches for a light press fit. This is really the best method.
Miscellaneous: Use a stock Chevy or aftermarket replacement clutch arm. I got a high-torque mini-starter from the local Autozone to clear the headers I ran. You may need to swap to an adjustable clutch fork pivot ball (available from Lakewood) if you use the 11/48-inch TransDapt adapter.