1950plymouth Posted June 26, 2019 Report Posted June 26, 2019 Hey there all! I'm new to the page and new to flatheads in general! I have a Canadian 1950 plymouth special deluxe with what I believe is the 218 flathead, the block measures 25 3/4 inch long. I live in Canada and I started the rebuild process of the flathead, got the deck resurface and bored .030 and all the good stuff, I ordered pistons for the engine, got .030 over piston and rings and they are smaller then my original pistons. I'm guessing the pistons I got are for an American engine? The bore is different on the canadian blocks if I've done my research right (after I got my parts of course). Any info you guys can help me with? I got all my parts from Andy Bernbaum, anyone know if he can get me parts for my canadian block if that is the case!? Quote
keithb7 Posted June 27, 2019 Report Posted June 27, 2019 This was a reply I got on another forum about the topic. “The Canadian branch of the Chrysler corporation got their own engine foundry in 1938. It made one engine only, the 25" long block used in American DeSoto and Chrysler cars. To get engines suitable for Plymouth and Dodge they reduce the bore to 3 3/8 from 3 7/16 and juggled the bore and stroke to get the displacement they wanted. They made crankshafts from 4 1/16 to 4 3/4 stroke. Each crankshaft had its own connecting rods of suitable length, the pistons were all the same. In other words if your engine has a 3 3/8 bore it uses the same piston as any other 3 3/8 bore engine, regardless of stroke. Likewise for the 3 7/16 bore. This means you can bore your 3 3/8 engine 1/16 oversize and use stock DeSoto/Chrysler pistons. Your engine with 3 7/16 bore and 4 1/2 stroke is equal to a 251 engine used in Chrysler, DeSoto, and Dodge trucks. The only larger option would be a 4 3/4 stroke crank which would give a 265 engine but these crankshafts are rather rare. Distributors alike and interchangeable but they changed the design every few years so points and cap don't interchange across the board. Distributors had specific part numbers for specific engines, so they probably tailored the advance curve for each engine. Model of distributor appears in the serial number plate rivetted to the distributor, good to know when ordering parts. Especially if someone swapped in a junkyard distributor years ago. Same engine used in Plymouth, Dodge, DeSoto and Chrysler cars, Dodge trucks, industrial and marine applications 1938 - 1972. Dodge Power Wagon Canadian military vehicles used the 251 engine up to 1972 and so did some heavy Dodge trucks to 1962. A lot of them were used in Massey combines and tractors, so if you see an old combine rotting away in a fence row check it out.” Quote
keithb7 Posted June 27, 2019 Report Posted June 27, 2019 What does your bore measure? 3 3/8? Possibly a 4 1/4” stroke? You may have the 228 engine. What is the SN info stamped in the block casting. Upper left side, near front of the block. Quote
dpollo Posted June 27, 2019 Report Posted June 27, 2019 (edited) Your engine started out with a 3 3/8 bore and a 4 1/16 stroke. If it has not been rebored already, an .030 overbore would be appropriate but generally a machine shop will not (should not) rebore until they have the new pistons on hand. For many years now, 3 3/8 oversize pistons have been hard to get, partly because the preferred solution was and is to bore to 3 7/16 which is 3 3/8 +,060 but also the standard bore for Chrysler and Desoto as well as later Dodge trucks and Industrial 251s and 265s. This has been my choice and in 50 years I have discovered that of all the bore and stroke combinations, 3 7/16 (3 3/8 +,060) by 4 1/16 produces the sweetest running engine. Few Americans have had any experience with Canadian 3 3/8 engines.... the 218 and the 228. When ordering parts specify a 251 and you will not go wrong for gaskets,seals, valves, chain water distribution tube oil pump and distributor. You can even use the newer head gasket with the bump on front. You may PM me if you need more information. Edited June 27, 2019 by dpollo more info 1 Quote
1950plymouth Posted June 28, 2019 Author Report Posted June 28, 2019 The number on the side of the block is P20 126800, I believe it is the 218 but maybe someone else with more experience can tell me for sure! I would like to keep the original crank, connecting rods, just need to figure out what size I need to bore and what size piston is available. Thanks for the help so far! Quote
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