How to identify 428 motor?

[AbodaTBird]

I am thinking about purchasing a 1966 Thunderbird and restoring it. I am interested in this one because the owner claims it has the 428 motor. I have attached a picture of the car and was wondering if there is a marking on the engine that would prove that it is in fact a 428 motor. The car is a Q code vin # but I want to be 100% sure that it does have the original 498.

Thanks in advance

[sseebart]

It's my understanding that the only true way to know is to measure the bore and stroke, which can be done (roughly) by removing a spark plug and gauging the movement of the piston. The 428 is externally balanced with weights on the flexplate, but I don't know if you can see the difference with the engine still in the car (via removal of the inspection plate.)

Since this is a Q-Code car, you might find some reassurance in the date codes on the block, if they are close to the assembly date of the car, it's a good sign (but not a guarantee) that the engine is original.

~Steve

[cacockrum]

As Steve points out, the crankshaft on the 428 is externally balanced by way of a weight near the outer edge of the flex plate. Also the flex plates are different: The 428 has 8 fairly wide webs that extend from the outer starter ring to the center hub, while the 390 has a solid plate between the two. If you can get underneath and remove the inspection plate, you might be able to see the weight, but if not you can easily see the difference in the designs. This still doesn’t guarantee a 428 since the 428 crank shaft / flex plate combination works in a 390 block, but if the date codes wok out it seems pretty certain that it is a 428.

[jtschug]

A 390 has a 4.05 bore and a 3.78 stroke. A 428 has a4.13 bore and a 3.98 stroke. You can’t measure the bore without removing the heads, but if you are careful, you can measure the stroke through the spark plug hole. You must be accurate because the difference is less than a quarter inch, but I have done it. Mercury made a 410 for two years which has a 4.05 bore and a 3.98 stroke. A Q code parts car I bought had one. However I wasn’t too surprised because it had Mercury valve covers and a 410 engine tag. If everything on the outside of the engine looks right and the stroke is right, then it is more likely to be a 428 than a 410

[vince]

According to the VTCI OFS for a '66 the engine block for a 428 will have a code 'C6ME-A' cast into it. The 390 is a 'C6ME'. The hard part is it is cast on the outside of the block about where cylinder 1 is. The alternator and other stuff make it hard to see. Plus may be lots of gunk which dripped down the block. Also, if you are under the car, the most likely way to be able to find and read, the casting numbers are upside down.

Good luck with your purchase.

[paulr]

When I first got the car I rubbed all the numbers on my block in order to see them. White paper and a carpenter’s (flat) pencil. It sounds lame but it worked!

[sleeper bird]

wouldnt it also have a c6 transmission?

[jtschug]

Some 390s in '66 also had C6 transmissions (most I think, but not all)