Thread: Did I buy a 428 and get a 390 Thunderbird?

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Okay, I am not an expert, but I thought I did everything right when I bought a 1966 thunderbird with all matching VIN numbers (6y81q138432). The car had a blown head gasket so I took the heads in for re-working. The machinist told me they were 390 heads. That started a sinking feeling that something was wrong. So upon looking at the engine cast: "C6ME-", I called him with that and he told me that in looking that up the book says the cast code was for "all Ford Engines EXCEPT a 428" Is there anyone who would agree with this machinist? I am very discouraged as I paid a higher price for the car for a Q code engine. Many Thanks.

All is not lost. Checking C6ME list a cobra jet 428 from 1966-70. It also list numerous engines from 352-390. I'm not a ford expert, so maybe others can help.

What are the casting numbers off the heads?


Bill S.

Originally Posted by afanoni

Okay, I am not an expert, but I thought I did everything right when I bought a 1966 thunderbird with all matching VIN numbers (6y81q138432). The car had a blown head gasket so I took the heads in for re-working. The machinist told me they were 390 heads. That started a sinking feeling that something was wrong. So upon looking at the engine cast: "C6ME-", I called him with that and he told me that in looking that up the book says the cast code was for "all Ford Engines EXCEPT a 428" Is there anyone who would agree with this machinist? I am very discouraged as I paid a higher price for the car for a Q code engine. Many Thanks.

You probably still have a 428 in the car. Early 428 blocks were C6ME-A like you said but its not a cj block. CJ blocks are usually C7ME or C8ME no big deal its just not worth the money a CJ block is worth but it'll take just as much abuse. The crank is really the only thing that makes a 428, 428cj, or 428scj shortblock anything special. 390's can usually take a 428 bore and then you just slap in the 428 crank and boom you have a 428. I say pull the pan and see if the crank has 1U stamped on it. If so you have a 428 crank just about the only real gold from that motor. Depending upon the 390 heads it has you might have poor man CJ heads. The casting number will be C6AE-R's, and these motors usually have 390GT intakes on them they have a big S "welded" on the runner. No real value in the 390 intakes as they cost more to ship than they're worth, but its a decent factory manifold. It just weighs about a ton. I hope you bought this knowing it was going to basically be a bored 390 with a 428 crank and not a 428 cj. I've owned about 4 of these 66-67 Merc's/t-birds with plain 428's in them that i got just for the 428.

but I did not mention too that my husband measured the stroke and it was under 4 inches! (3 and 7/8) Well, we only had a cheesy tapemeasure and not a micrometer. I told the machinist that and he said that is not acceptable to verify. Since I have to put it back together obviously, and make decisions as to re-ordering parts, he wants to be sure he orders the right thing. He will only accept the crankshaft for verification. Also, the intake manifold says C6AE 9425-G. It will become obvious I know NOTHING about engines! I read the posts and can see there is alot of respectable expertise out there, but this machinist seems dead set on his idea too and I a little afraid to challenge him since I don't know anything. That bore measurement convinces my son and husband that I got taken!

NO "A" after the dash mark, it is C6ME only. There seems to be an obvious grind mark after the dash though.

on the intake manifold and it says 390 66 6 6 b 357 S.

Originally Posted by afanoni

on the intake manifold and it says 390 66 6 6 b 357 S.

If you found the tag on the engine and it says 390 it sounds like you have a 390. On a side note it sounds like you have a 390 gt intake on the motor worth $50-75.

it seems there are too many things that point to the 390, but does anyone know why the machinist is not satisfied with anything other than a piston and/or a crank number? It seems obvious enough with the stroke measurement and his response to me was: A tape measure is a tool for carpenters and I ain't a carpenter" boo hoo.

I just talked to a person referred to me who is quite involved with T Birds and clubs and all. HE says the Engine block I have C6ME is a Mercury Block and could have a 428 crank in it. He referred to it as a 410. He also says to look for counterweights on the flywheel. And I do NOT like to get under the car because it wrecks my hair and my hands, but what do you think of the other ways of finding out about the block. I guess we are certain the intake manifolds etc.. are 390-ish, but are they built that way? Why would this happen?

one reason this would happen is a lot of fiddling fingers over 40 years.

Either way it looks like you are going to pull the motor to do a positive I.D. check.

Its a bit like the theory about eggs in the birds nest, you could surmize all the reasons why there are eggs in the nest, but untill you actually climb the tree and look you dont really know.

Sorry i forgot to post the link to the info i was talking about. http://www.428cobrajet.com/id-flexplate.html

Hey, get yourself a 6" dial caliper, whether you have to steal, beg, buy or borrow one. Have someone to bring any piston to top dead center by putting a socket and ratchet on the bolt at the front of the crankshaft that holds the harmonic damper onto the crank. You can stand by a cylinder and keep checking that you are close to TDC on that cylinder by checking with the depth function of your caliper. It probably will never come to zero, because the manufacturer of the piston will have made if to that it will not come to the deck of the block at zero, but make it come as far to the block as possible. When you have TDC, record the reading on your dial caliper from the top of the deck to the top of the piston. It may be 0.020", 0.025", o.030" or whatever. Now, have your helper turn the crank to move the piston to bottom dead center. Move it around a little to be sure you are at BDC. Record that measurement from the top of the block to the top of the piston. From that figure, deduct the figure that you had with the piston at top dead center. For a 390, the stroke will be 3.780", for a 428 it will be 3.980". Good luck and sorry about your hair and nails.

Hey guys, how did I do. I clicked those figures off without referring to anything.

Oh, many thanks for all that- that is all useful BUT I still have a question! Why is the tape measure of having the piston all the way down perfectly, using a level for the corresponding piston to be all the way UP, inadequate. It is 3 and 7/8 inches at MOST and that is just too far off the requirement of 3.98 inches that even if we were off a little, it is not close enough to feel right about. Does that seem reasonable? That we could squeeze another 1/8 inch? And what about ANOTHER suggestion, that the pistons should have a marking on them that shows they are bored .003 over. THEN another guy said the 6cME is a Mercury Replacement Engine?? Oh, and the last time I got under that car, it is on a horrid driveway on a building site, the weeds in my hair were so frightful my son blew me off with an air compressor and it was equally horrid. He is an engineering student at Seattle U and thinks he knows everything, but I am finding that he is way over confident this thing IS a 390.Too many brains!

O.K., a 390 is 3.780", your tape measure is 3.875" and a 428 is 3.980". You choose. And again, sorry about your hair and nails. I'm just trying to tell you the correct way to do it. I can sympathize with your machinist.