Some time around Y2K, I popped the original (flat-tappet) engine in my '88 K1500 5.7L. I ordered a "service replacement" 90--92 5.7L Caprice/Roadmaster TBI engine (roller cam) from Pace Performance. I also ordered a Melonized distributor gear, recommended by their Parts department. The engine and gear show up, and of course the gear is intended for the older, .491 distributor shafts--not the ~.429 distributor shafts of the TBI and Vortec distributors.
So I call Pace again, and after a couple minutes of research, the guy says that all TBI distributors have Melonized gears, and that my original distributor will be completely acceptable if the gear isn't already worn. I crammed the original TBI distributor into the Caprice long-block. Eighteen years later, that engine pops a head gasket. I freshen-up a Vortec short-block, and reuse that same distributor. Sometime shortly thereafter, that distributor failed the pickup coil or module, I merely replaced it with another well-used distributor I had on the shelf. Several years later...still working.
So while my evidence is not conclusive, and relies on only two samples, I'm reasonably confident that TBI distributor gears are perfectly suitable for use with steel-core cams provided the gear doesn't already have excessive wear from dirty oil or a million miles.
Good back story providing valuable insight. Of course nothing lasts forever, and we're talking a service life of 15 years,
not 15 hours, days, or weeks after an engine swap. And I'm guilty of conjecture based upon a couple of blurry pics.
For the record, "Melonizing" is just a coating applied to the cast-iron distributor gear, it's about a thousandth of an inch thick, maybe less.
On the bright side, while trying to come up with an answer to the metallic debris in the engine oil I went down the melonizing rabbit hole.
And I found
THIS, which led to a succinct yet informative
process description, where they discuss the depth of the treatment.
Of course, just like the different grades of stainless steel, no doubt that there is affordable/offshore Melonizing, and then there is the
no-kidding version? (And during the Melonizing deep dive this reminded me of the Tuftrided crank journal discussions back in the day.)
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I'm here to learn more about all things having to do with GMT400 powerplants, focused on increased power delivery, street driveability, & longevity.
Thanks to everyone involved I've got a much finer appreciation for what you have to pay attention to when trying to move power in a modern
day roller cam SBC/BBC in a 90° angle from cam to dizzy > oil pump.
Good stuff. It's appreciated!
