I have a 1978 F-150 with a 400m. I am using the original front cover (some people call it a timing chain cover) and when I bolt up my water pump I have a leak. The leak is at the bottom between the two threaded bolt holes located right above the crank hole. There is the slightest depression between these threaded both holes and I am being told by car quest that I also need a Backing plate to go between the water pump and the front cover. If I am remembering correctly I didn't have one when I originally pulled it off to replace it. Anyone out there no for sure if they cam stock with a backing plate? If they did I have had zero luck finding one online or in brick and mortar stores.

 

First, (and no offence), it's a 400....no "M" involved. The M goes with the 351.

Car Quest got bought out by Advance Auto....Both have/had meat heads for counter people. Maybe they replaced one bonehead with another. (no offence to the real counter people out there.....I know there are a few). You have no need, desire, or was there any "backing plate" there from the gate. That metal front cover was the only thing there.

What might have happened is that it may have gotten over tightened, causing a slight warpage (it happens....to the bottom part, too - where it meets the oil pan). 'Cause it's the only two bolts with 1/8" thick metal that holds the bottom of the water pump on. Best scenario - slap it on yer anvil and straighten it out, being careful of the threads on the inside. Otherwise, double gasket it with some RTV between the offending space.......snug up/ torque accordingly....20 foot lbs I think?

Oh, and welcome to FTE.

 

Thats what I planned on doing once I figured out whether or not it actually needed the plate. The "warp" or "depression" is slight enough that I am willing to use a gasket along with RTV. I knew they had to be mistaken. I was able to confirm with a ford tech specialist as well.

Oh and the "m" is something I've heard debated at great length. Is the same block as the 351m and from the same 335 engine family from what I've read. What I don't get is what exactly is or isn't modified? 50% of the time the parts supplier designate the engine 400m and the other half its just a 6.6L 400.

Thanks for the feedback! I appreciate it.

 

You're welcome.

The 335 series started with the 400 and the 351 Cleveland. Smog and junk came around and Ford "destroked" the 400, thus making it a 351 "modified", lower compression and all that jazz. The 351M has a 3.50" stroke, 4.00 bore while the 400 has a 4.00" stroke and a 4.00" bore. The pistons on the 351M are different, too. In fact, the only difference between the two is the crank and pistons. Both use the same block.

Good luck.

 

Yep, that is correct. I have loads of Ford documentation that talks about "351M" and "400", but no "400M". The reason appears to be that Ford only put a qualifier on the name when there was another of the same cubic inch to confuse. The 460 and 390 were always called exactly that. But they already had a 351, so calling this one a 351 as well would cause confusion.

The debate is really whether the "M" is modified or Michigan. Most say Michigan, as Ford had a habit of naming their engines the name of the plant where most were cast. For instance the 351W was cast in Windsor and the 351C in Cleveland. And, sure enough, the 351M's were mostly cast in Michigan. Read about it here: M-Block 351M/400 Parts Reference

 

TMeyer sells new covers and I would recommend you buy from him since he supports the 400 community. That said, Summit Racing had new timing chain covers listed as in stock, about $125 but shipping if free on anything over $99. You can try to straighten the cover but I've found that it's such a PITA to replace one twice you might as well put on a new one.

 

I ended up using RTV with another gasket and it did the trick. My engine cover/timing chain cover didn't seem to be the issue as much as a faulty gasket. Thanks guys!