Can anyone help me check a few things on a 351M ?

I just bought the makings of a 351M engine that was suppossed to have a turned crank and a ready to go short block.
Once I unbolted everything...
It needs turned!! and the original bearings are even missing!!

Anyway I got a lot of good stuff with it I will probably sell the whole lot.
I want to make sure the rods are in fact 351M rods.
What is the length of a 351M rod?

 

Car,
351M con. rod Ctr to Ctr 5.778 inches (forged steel).
400M con. rod Ctr to Ctr 6.58 inches
KingFisher

 

Moved to Cleveland engine forum.

 

This is not correct.

The 5.78" rod is the 351 Cleveland rod.

Both the 351M and 400 use the 6.58" rod.

All 335-series (351C/351M/400) connecting rods are forged steel.

 

I recently blew up a 351M. I bought a 77 truck with the engine in it. the engine had been rebuilt completly with a new eldebrock carb. the engine had alum. pistons eldebrock 400 intake and cam. I was pullin hard on the truck one day. I took it home a very short trip home and left it set. the truck ran fine a few days later then it started to spark knock. I couldn't get it to come out of it no matter what I did. changed everything on the ignition, still didn't seem to help. finally I was taking the truck around the block in frustration and it felt like something left loose in it and then it died. I popped the hood and it had antifreeze all over the top of the engine although you couldn't see where it came from. I got back in the truck and drove it home. I pulled the plugs and #5 was pressed up and #6 had the end at off. I tore down the engine and discovered that number 6 had melted pretty good. the head gasket was blown between 5 and 6 and had worn a groove in the head as well as the block. 5 along with 1and 3 looked to be running lean while the other pistons looked rich. what caused my spark knock? some say the new carb is messed up leaning out the 4 cylinders. others say I just blew the head gasket? I tried putting in octane boost also thought mabye some bad gas. I don't think I was running to much compression with 140 pounds. whats your opinion? what could I use off my 351M in changing to a 400? thanks

 

Thanks for the reply. It helped. I do have the longer rods for the 351M and 400. So to make sure, can you measure the crank in any way? I can't find the casting mark on the #1 throw. I can just make out an A on the edge. Can the pistons be measured too?

 

If the engine was disassembled when you got it, there's no guarantee that crankshaft goes with those pistons.

To find the ID code, I'd suggest cleaning the entire surface of the front counterweight and first throw with a solvent like naphtha or acetone to remove all oil residue, and then examine the casting closely for the ID code.

The crankshaft ID code is cast into the surface, which means it was part of the mold, and not stamped or machined into the metal after the initial casting. Sometimes, the casting ID code is a little faint.

Often the counterweights are machined to balance the engine at the factory, and it's possible the ID code was in such a location on the counterweight that it was machined off. In that event, measuring the crankshaft throw is the only way to identify the crankshaft.

If you've got some main bearings, the easiest way to measure the crank is to set it in the block, on the upper main bearing halves, and measure the location of a rod journal relative to the same spot on the block (e.g., the edge of the oil pan flange), at two crank positions 180 degrees apart. That gives you the stroke measurement, 3.5" for the 351M, 4.0" for the 400.

Or, you could try placing a straight-edge across a crank throw, along the centerline of the main journals. Place another straight-edge across the throw along the centerline of the rod journal, and measure the distance. Throw length is half of stroke, 1.75" for the 351M, 2.0" for the 400.

 

Thanks again, after doing some of the measuring I figured it was the 400 crank. Then I looked at the #1 throw weight and found the marking 5MAB, so now I'm sure it's the 400 crank. After measuring all the other parts, I'm sure they are 351. So I got a lot of good parts with the deal, but not exactly what I was told.

Thanks for all of the help Bubba F250 and others