My 79 F150 4x4, purchased before this last Christmas has had a noise like an exhaust leak. I put in my vacume gauge, and showed a bad vavle problem. Put a dollar bill into the exhaust (true duals/headers) and showed to be the left enging bank was the problem.
Removed both heads and fou a burned valve on the left side. Finally the question. The truck for the most part is a Hienz 57. Engine is supposed to be a 400, but I really don't know for sure. Heads are going to a machine shop this week to be gone through. Also found a bad lifter, and thinking about installing a hotter cam. But I'm not sure what the engine is for sure.
How can I find out what this thing is for sure???
Bob

 

Shouldn't matter. Externally the 400 and 351M are identical. I believe even the cam is the same.

 

yessir, you are right, the cams are all the same for clevelands 351m's and 400's, since you have the heads off the block anyhow, the easiest way to tell what you have is to measure the stroke, the blocks are the same for the m's and 400's sharing the same bore too, only difference between teh two is the pistons and crank, they share the same rods and all, you'll be able to tell what you have by measuring a cylinder thats at bottom of the stroke or bottom dead center, a 351m is a 3.5 inch stroke whereas a 400 is a even 4.00 inches, as for the cam, i'd say go for it, but the biggest thing you can do for those ole motors is get a timing set that willl allow you to run the cam straight up or 4 degrees advanced, because ford instituted a 4 or 8 degree i cant recall right off, retard into the stock timing sets, i ran into that problem myself when i installed the new cam in my 79 f-250, just didnt run to its full potential, have to wait til i get back from this deployment to do anything about it though, anyhow, hope these things clarify some of you questions