Greetings Gentlemen! Ive been gleaning valuable information off of here for some time now since getting myself an old pickup camper combo that runs on propane. After modding the propane system to run correctly it was time to tackle the head gaskets- when the fun began.

I was told the truck was a 351W when purchased. But when the valve covers are removed they've got a letter M stamped on the heads. It has a dry intake and valley as well. I order in a new head set for a 1980 351M/400. I check the old gasket against the new gasket, and they are identical. But here's where it gets interesting. If you look at the photo Ive posted, you can see that the gasket holes are only 2mm, where as the metal coolant openings are perhaps 10mm >. The coolant openings on the lower left bottom are completely restricted. There are 2mm holes in the gasket that have no corresponding coolant opening around the cylinder. If you examine the failed rusty gasket areas, you will find associated with each failure the small gasket holes with no corresponding openings in the metal. And with the restricted coolant passages it just seems to eat into the gasket hole. In short, is this not because I had, and have, the wrong head gasket?

The parts guy thinks Ive got the correct gasket by the numbers, but he also agrees that the gasket integrity is compromised by having gasket holes were they shouldnt be, and by having the gasket restrict the hot coolant.

I'm wondering if someone could tell me if Im way off base and the differences mean nothing, or if I need to modify the new gasket to accommodate the correct size coolant openings etc...

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FYI
The coolant outlet on the 351W exits the intake manifold, and on the 351M it exits the block.
The 351W fuel pump bolts are horizontel, whereas the 351c, 351m/400 are vertical.
The 351W uses a cast timing cover similar to the 302, whereas the 351c and the 351M/400 use a flat cover with the gear housing cast intergrally with the block.
The 351W has 6 valve cover bolts whereas the 351c, 351m/400 have 8.

 

dont modify the gasket. they dont match the size and shape of the coolant ports.

 

Brown - I can't see the photo so can't comment on it. But, I have a set of new 351M/400 gaskets, Felpro Permatorque, laying on the bench. So, I can take pics or whatever to compare - if I could see yours.

But, you do need to confirm you have an M not a W.

 

Sorry about the picture delay gents, bit of a learning curve on the software... here are 4 pics put into one to show the different items.

The heads have the letter M for Michigan or Modified stamped in the corners. There is no coolant in the intake manifold- it all sits on top of a valley pan which keeps it "dry".

The block has the numbers D7TE-A2B stamped near the starter. The intake manifold has the numbers D7TE-SA & firing order numbers 13726548 stamped on them. The heads themselves have the large letter M stamped, and the number Mc 0813, the gasket side shows D5E A3A.

 

If you have the M-block engine (offhand, it looks like you do) yes, the oddities you describe are intentional & correct.

As you've noticed, the M-blocks have a dry intake manifold - coolant doesn't cross via the intake manifold.

As such, the water flow is routed & controlled differently... the 2 mm holes covering the 10 mm holes, the blocked passageways, all of that is completely by design.

There aren't separate left & right heads, either head can be installed on either side.

You need to ensure the gaskets are installed properly! There should be FRONT stamped/printed somewhere on the front, near the square hole.

I also have an M-block 400 and was curious about this stuff, too.

 

Thank you Ctubutis! So Im guessing that the gasket is actually a mod then from original gasket design?

 

Oh, I don't know, I was never a powerplant engineer in a prior life.

There may (or may not, I really don't remember) be some stuff in the 335 forum's sticky.

 

Sounds like you have everything sorted.