dar83501

I just bought an Olds Big Block to drop in my '87 Oldsmobile Cutlass Supreme (yes, it will fit...I'll MAKE it fit).

This engine is definitely an oldsmobile big block, but my research on figuring out what exactly it is has thusfar been pretty inconclusive. If anybody can help me out, I'll describe what I know about the engine, and what casting numbers I've found on it below.

This engine was rebuilt approximately 20~25k miles ago. I was *told* it came from a late 60's car, and is a 455. The engine has several contradictory things about it which confuse me as to what it actually is.

-Flywheel bolt pattern is a 6 bolt, and using calipers it appeared that two of the bolts were offset roughly 1/4" or 1/8".

-The engine had "B" stamped heads. The 455 didn't come with B heads, the 425 did. I do know they are interchangeable however, and it is very likely when the engine was rebuilt, that they placed 425 B heads on it if it is indeed a 455. I have heard they are nearly identical to C heads. The numbers on the heads and the numbers on the block do NOT match.

-There's an Edelbrock Performance 455 Olds intake manifold on this engine. This doesn't mean much, because the 425 and 455 are the same block.

-The following identification numbers have been found, and my understanding of them:

1.) On the back of the block, behind the flywheel, on the bellhousing, upper right hand section, is the following:

F 3
A

The F and A appear as they are, and the 3 is offset and tilted towards the F.

My understanding is that all oldsmobile 455 blocks were marked with "F".

I have no idea what the "A" and "3" signify.

2.) On the back of the block, below and to the right of the distributor, the following is marked:

5

241

CFD

My understanding is that the 241 is Julian Code for 241st day of the year, making the block's manufacture in August or September some time, but I have no idea what the "5" or "CFD" stand for. These numbers/letters appear as above.

3.) On the front of the block, centered directly above the water pump, is what I understand is the engine casting number. it reads:

389244D.

The "D" on the end is quite large.

According to my research:

the "3" stands for Oldsmobile Division of General Motors

the "8" stands for the last digit of the year the motor was produced, making this a 1968 motor.

the "D" stands for the production plant, which I believe in this case was a plant in Georgia.

I also understand that the last six digits correspond with a chunk of the original vehicle's VIN.



All my research on the casting number "389244D" has resulted in a supposed 425ci motor.

This doesn't make sense to me, because I thought the 425 engine was dropped in '67, and the number on the casting would make this engine a '68.

My theory behind this, is that the motor was produced towards the end of '67, to be placed in a '68 vehicle, making it a 455. When the engine was rebuilt, they decided to replace whatever heads were on it with B heads from a 425.

Any clarification or help would be greatly appreciated!

Edit: I forgot to mention, one possibility I have thought of is that this is actually a 425ci engine, with a 455 crank and flywheel. I have not removed the flywheel yet to check for markings on the crank.

64Rocket

The block is a '66 -67 425. When you pull the flywheel, see if the craank flange has a Cut out area in the shape of a check mark, or a "U" shape cut out or it may look like a "C" shape.
Check mark shape = 425
"C" shape = 455

Geno..

joe_padavano

First, the "F" marking on the back of the block was used on just about every Olds motor, not just 455s. Second, the "389244D" number above the water pump is NOT the VIN-derivative, it's the block casting number. VIN-derivatives were not used prior to the 1968 model year. The VIN derivative would have been located on the SIDE of the block and is a STAMPED number, not a raised cast number. It would have been difficult to change the cast number for every car, especially since the VIN derivative wasn't assigned until the motor was fully built and mated to a car. You should also have been tipped off that the letter indicating build plant is in the THIRD position on the VIN-derivative, not the last.

As noted, you have a 425 block. Assuming the "B" heads are original, it would be a 1966 motor. It is possible to install the 455 crank, rods, and pistons in a 425 block (and vice-versa). Either will be a nice motor. The 425 crank is forged, the 455 is cast. The two cranks have a different flywheel flange bolt pattern, so you need to use the matching flywheel. Otherwise the two motors are externally identical.

dar83501

Today I'm going over to the shop to do some work on an old Subaru wagon, so I'll bust out the impact wrench and pull the flywheel off the olds block while i'm there and take a look at the crank. I greatly appreciate the info.

When I get a look at the crank I'll post what I find here. I have a feeling when we tear the block completely apart i'll find 455 internals, but it was originally a 425.

Thanks again for the help!

dar83501

Well, it took me a bit longer to get to work on the subaru than I thought it would, but that always happens. After we got done with that car, we pulled the flywheel off the big block (which took a little over a half an hour...that thing was on there SOLID). On the crank flange, there was a big "C" shape cut out.

I imagine I can safely say that what I have was originally a 425 block, but when it was rebuilt it had 455 rods, pistons, and either a forged crank, which I hear was the best kind, or a plain jane cast iron crank. The guy I bought it from said it was a monster of an engine, and it tore 2nd gear out of one of his TH-400 trannies, so I'm thinking this engine may be cammed up and/or bored out as well.

We're getting it off the homemade engine stand contraption that it's sitting on sometime soon and putting it on a real engine stand, at which time I'll pull off the oil pan and figure out exactly which of those cranks I have.

Anyways, I'll keep progress on this car posted.

64Rocket

If you have the "C" cut out on the flange, it is a cast crank. No big deal, it is a very good crank. Does look like a 425 block with 455 internal. Still makes it a 455. Strange somebody would do that, but it works.
Sounds like it is good to go. Hope they didn't beat it to hard.
Geno..

dar83501

I don't think so, the guy I bought it from said this engine didn't have more than 20 or 25k miles on it. it doesn't have that much grime on it either, so i'm going to believe it.