BigHog, look for a machined pad just aft of the distributor and sort-of behind the dipstick. There should be a stamped engine serial number on that which will help ID specifically what the engine is. The casting number that definitively IDs the block is low on the passenger side, between (and below) the distributor and fuel pump, and is usually obscured and hard to read (so the stamped engine serial number is the next best thing). There will also be a cast-in date code (in the form of something like E 10 5, which would decode as May 10th 1955, as an example) on the passenger side, just above and a little in front of the starter.
If you can ID the engine, that will help with a few questions, such as fiber vs aluminum timing gear and whether the cam is cast iron or steel, and what distributor gear should be used to match (as well as what the distributor PN should be, which is stamped on the breaker plate). For example, if it's a '55 235 first series truck engine and not modified, it would have a cast iron solid lifter cam (not the early steel cam, and not hydraulic lifter), and would have a Delco 1112388 distributor, per the parts manual. Hope this helps as you get farther into determining what caused the distributor gear to fail.
But, I'll echo some earlier comments - I've never seen a failed distributor gear in a 216/235/261 before your photos, and even in very worn distributors, the gears generally look fair to good, with some wear patterns visible. I'm thinking, similar to Jerry, that something had to have seized or nearly seized on the distributor/oil pump side of the distributor/cam gear combo to have the distributor gear shatter like that. Normally, there isn't a huge amount of resistance to rotation. Can you easily turn the distributor shaft in the distributor body, now that it's out of the engine? It should turn with light resistance. If that turns freely (and the shaft isn't so worn/loose that it might tilt and bind), then I think Jerry probably hit the nail on the head. I know it would mean the pickup screen would have had to fail, but perhaps something hard was sucked into the oil pump, locking it?
Last edited by drdoug; 03/02/2019 9:30 PM.
