I found this board researching Nailhead info. Looks like a lot of good stuff here. I've been researching a couple of Nailheads I have acquired. I'm pretty sure one's a 425, and the other is 401 or a 425. I'll probably post the casting numbers over in the Nailhead section. I also just acquired a "barn find" 2x4 setup with the matching valve covers and air cleaner assembly. Anyway, glad to be here, and hope to find lots of good info.
Are the motors complete? The bore size should tell you instant if its 401 or 425 as they have the same stroke. What colors are the motors? There were 2 made in 1966 that were red. A 425 in 66 Riv and the 401 in the 66 Skylark GS. Welcome!
Easy way to tell if it’s a 425 is to look for the rectangular boss on the bellhousing mount. It’s about 1” X 1/2” and has a little bit of a pyramid appearance to it.
PGSS, no they are not complete. I rescued these from a scrapper who was sending them to be recycled. they are so weathered it's hard to tell the color of one. The other more complete one is the early Buick color. Nailhead in a 67, That casting # chart is what brought me here!! Thanks! Smartin, I'll look to see about the rectangle boss on the bellhousing when it stops raining and snowing. Thanks everyone for the welcome!!
Cool saving more Nail Heads!! Not many were painted red. A quick bore check on the 425 is "4.3125" and the 401's are "4.187" Curious to know what you have
Interesting article about Nailheads: Confusion Over Square Boss On The Bellhousing Some think that if there is a square casting boss (or bump) on the bellhousing - then you must have a 425. This is not always the case. See the pictures below. This 1966 401 has a square casting boss. The first picture below shows the square boss at the left. The second picture below clearly shows the block casting number. This engine is not a 425! Measuring the bore and using the engine code letters stamped at the front of the block confirm that it is a 401. Note the lifting eye that is cast into the block - this is a 1966 only feature. 1964 425 Casting Boss In the two pictures below you will see the casting boss on a 1964 425 block. Note the difference between it and the 1966 401 block shown above. 1963, 1964, and 1965 425 blocks will have a boss that looks like the one below. 1966 425 Casting Boss The 1966 425 block has two bosses adjacent to each other. See both pictures below of a 1966 425. Note in the second picture that the square boss is about half as tall as the rectangular boss. Note that the casting number is 1364704. The lifting eye cast into the block is a 1966 only feature. 1963 425 With Rare Casting Number See the pictures below showing the bore and casting number of this 1963 425 block. It has an uncommon casting number.
