M-Block 351M/400 Pictures

Engine block photo archive

Copyright 2002-2003 Dave Resch
All rights reserved.


MCC Block Casting ID Code

This is the block casting ID code for a '77-up MCC truck block (D7TE-A-2-B). Notice the code appears upside down, about an inch and a half below the deck, on the right side of the engine, toward the rear. If this engine was installed in a vehicle, you wouldn't be able to see the block casting ID code without removing the starter.

All blocks designed for trucks have the D7TE prefix. Truck blocks have a revised #3 main (thrust) bearing support web to withstand the additional thrust load imposed by a clutch.

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Build Date Stamp

The original build date of the engine is stamped into the front cover surface, toward the right side of the engine. Often this stamp is behind the front cover gasket so it is not visible with the front cover plate on the engine. In this case, it was outside of the front cover gasket.

The build date was the date on which the engine was assembled at the factory. The build date code in this picture is: “78G190” This translates to July 19, 1978.

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Block Features (right side)

  1. Upper engine mount boss. Engine mounts attach to the upper boss and two lower bosses just above the oil pan flange at the bottom of the block (arrows).

  2. Threaded plug into the water jacket.

  3. Lower accessory bracket mounting flange on right front of block.

Just above the "3" is the oil dipstick hole used for front-sump applications (i.e., cars and pre-1980 4x2 trucks).

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Block Features (left side)

  1. Upper engine mount boss.

  2. Threaded plug into the water jacket. This plug corresponds to the one on the right front of the block (previous picture).

Threaded plugs in the lower water jacket might have been intended to support an alternative cooling system, such as in a marine or industrial application.

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Block Features (front)

  1. Plugged dipstick hole used for cars and pre-1980 4x2 trucks with front-sump oil pans. All '80-up trucks require a rear-sump oil pan to clear a crossmember, so all '80-'82 M-blocks use the left side, oil pan dipstick mounting.

  2. Coolant temperature sending unit.

Note the circled area with no raised web beside the distributor hole.

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No Web on Block Front

Many M-block (351M/400) engine blocks have a 5/8" tall raised web just left of the distributor hole, on the top of the block. However, not all M-blocks have that web, as this photo (and the previous photo) of a 1978 MCC block shows.

Some people say you can distinguish an M-block from a 351 Cleveland block by that web. It's true that no 351 Cleveland blocks have that web, but not all M-blocks do either. While presence of the web rules out a 351 Cleveland, absence of the web does not rule out an M-block.

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Web on Block Front

This photo of a 1979 CF block shows the raised web to the left of the distributor hole on the front of the block. The raised web is an extension of the engine block’s front intake manifold gasket surface.

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Oil System

This picture of the front of the block shows the oil gallery casting bosses. All oil galleries in the block are drilled through the raw casting.

Arrows show the path of oil when it leaves the filter. Oil flows from the filter adapter on the left side of the block, into the crossover gallery that runs above the crankshaft, over to the right side of the engine. From there, oil feeds the #1 main crankshaft bearing below, and the main distribution gallery (right side lifter gallery) above.

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Crossover Oil Gallery Port

This picture shows the left front side of the block. Toward the front, on the side of the front cover housing, is the fuel pump mounting hole. Beside that (arrow) is the outer end of the oil gallery fed directly from the filter. To the right is the oil filter adapter. The center passage in the oil filter adapter is drilled into the crossover oil gallery.

The end of the crossover oil gallery is usually plugged on the side of the block. This is where you can tap into pressurized oil for an external oil line to help feed the rear mains.

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Oil Pressure Sending Unit

This picture shows the oil pressure sending unit on the top rear of the block. The arrow indicates the oil gallery that feeds the sending unit from the rear end of the main distribution gallery (right side lifter gallery).

An external oil line can feed pressurized oil into this port, providing higher oil pressure for the last two main crankshaft bearings.

Using an external oil line will improve the longevity of the main crankshaft bearings, even on a stock-level rebuild.

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Crankshaft Casting Marks

  1. Cleveland Foundry (CF) mark on #1 main bearing cap. Main bearing caps #1 through #4 are marked with the position number, an arrow pointing toward the front of the engine, a foundry mark, and sometimes a date code. The date code on this cap is 8F12 (June 12, 1978).

  2. Crankshaft ID code (1KA) for a 351M crankshaft. The 351M ID code is cast into the side of the first counterweight. Just below the casting ID code in the picture is a letter "H" stamped into a machined surface. That is probably a quality control mark.

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More Crankshaft Casting Marks

  1. (and 3.) Machined and drilled parts of the rear crankshaft counterweight. These are adjustments to balance the crankshaft at the factory.

  2. Cleveland Foundry (CF) mark on #5 main bearing cap. The #5 main bearing cap is usually not marked because it is unique, wider than the other main bearing caps, with a groove for the rear main seal. Note that the main bearing cap in this D7TE engine is the original 400 design from 1971 (D1AE-AA).

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Connecting Rod Casting Marks

The casting ID codes are clearly visible on this rod end cap. Once again, note that the connecting rods in this D7TE engine are the original 400 design from 1971 (D1AE-AA). Many M-block components did not change significantly from the original 400 design.

The machined surface in the middle of the connecting rod end is evidence of factory balancing.

Sometimes, you can find a casting date code on the other side of the connecting rod end from the casting ID codes.

Cylinder Wall Valve Relief

M-block and 351 Cleveland cylinder walls have a valve relief notch cut into the upper edge to allow clearance for the intake valve’s head.

Even the smaller M-block and 351C 2V intake valves (2.041" head diameter) are rather large compared to other engines with similar displacement.

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