I'm planning on rebuilding my 351M this fall and want to know if anyone has some good tips before I begin. This will be my first rebuild so any info will be appreciated. Also if you have any suggestions for a good rebuild kit.

 

Two suggestions. Unless your really attached to your 351M, consider picking up a 400 block or rebuilt short block. You'll pick-up about 50 cubes and the engines are otherwise identical so you can reuse your accessories.

You may also wish to consider installing a mild cam, dual plane intake, and street legal four barrel carb. You won't believe how much better the engine runs with just a carb/manifold switch.

I would also recommend picking up a copy of "Ford Performance" by Pat Ganahl. Its a little dated, but it has a lot of good info on the Cleveland Engine family.

 

I would stay with the 351. Yes you lack 50 cubes but guess what?? More cubes eat more gas. And when you are a junior in high school gas is like gold especially when I have to drive 27 miles to school. An RV cam or some other mild cam will help with low end torque and even ups your mileage I had a friend that got 14-15 with his 400 running headers and an RV cam. Not too bad but you should be able to get 17-18 out of a 351. If you have any more questions just ask.

Fordman

 

If you can afford it and don't mind running better gas you might look into getting a pair of Australian 2bbl Cleveland heads. They have the small combustion chamber of the 4bbl heads to increase the compression ratio but retain the 2bbl intake and exhaust port sizes to keep the bottem end down where it needs to be. They would be direct bolt on replacements to either a 351M or 400. A set needing work should run around 100-200 buck or a completely reworked set should be in the 800 to 1300 range (last time I looked into them)

 

I read in an article that the 351M block and the 400M block are identical in every aspect. The difference is the stroke in the 400M crank. The 400M crank has a huge stroke and therefore increases the cubes of the engine. So ideally if you found a 400M crank and pistons the engine would in theory become a 400M engine.
I was researching a rebuild on the same engine in my 1977 F250 Explorer 351M/C6.
And I found a lengthy article on the M block engine. It was on this site somewhere but I can't find it today.

 

If this is your first rebuild recommend you keep everything stock and original. Mixing and matching parts introduces variables which may result in unexpected problems and will also drive up the cost of your rebuild. Avoid the common mistakes of the novice builder---
Put all parts back in the same place i.e. same rod caps on same rod, same main bearing caps on same main web, same rod/piston in same bore (should be numbered) and properly oriented. Torque everything to spec, torque heads in proper sequence and progressively. Use plastiguage to check all bearing clearances. If your engine is pre-1977, put in hardened valve seats and stainless exhaust valves to be compatible with unleaded gas. Put on new valve springs. If any bore is rough or worn more than .010 at the top, definitely bore out all cylinders .030 and get oversize pistons and rings. Ensure new pistons are oriented properly on the rods. Check ring gap in the bores and properly orient ring gaps on the pistons. If just doing a ring job, be sure and scuff the cylinder walls (glaze break). Put in a new timing set and oil pump. Check valve lash at the rockers. Before starting, prelube by rotating the oil pump shaft with a drill, or at least rotate the engine with the starter with the spark plugs out. When installing the distributor, be sure you are at TDC and also on the compression stroke. After starting, run the engine at 1500 rpm for five minutes, shut down, check fluids (water and trans fluid), restart and run another 25 minutes, idle down, set timing and carb. Do not idle your new engine for a prolonged period of time. Did not mean to ramble but hope this helps. By all means, go for it. Built my first engine (a 312 y-block) in 1968 and made every mistake possible.
FL Panhandle

 

This may sound stupid but what is a RV cam? I am interested in better gas mileage so that's why I'm interested.

 

I should have clarified--RV cam refers to the style of the cam. You can get different durations and lifts with them. Just pick out the one that gives the most bang for the buck.

Fordman