ID on an olds smallblock

[Guest]

Can anyone give any assistance or point me to where I might find out how to ID a small block that I just pulled out of an '80 olds 98... The engine is at least a rubuild (judging by the amount of RTV blue squeezed out from beneath nearly all gasket surfaces!) I steam cleaned it, and, wirebrush in hand looked it over pretty carefully. The only numbers that I found were: On the right side of the block, between(and slightly above) the rear two freeze plugs is stamped 5L in large letters (I'm thinking this might mean 5.0 liter which is the 305....) and on the left side of the block, at the front corner, just below the head, there is a boss with the number 3EM266131 stamped into it. It uses a small block starter, I am certain of that, as one from a known 350 olds will not work, and one from a 260 does...

Any assistance in finding an ID on this little beast before I stick it into a truck will be appreciated. Feel free to e-mail me with your answer, and I will check this BB regularly. Thanks,

Montana Andy

[rocketraider]

It's probably a 307 since that was standard in a 1980 98, and the only Olds to get a gas 350 in 1980 was the 442. See if the numbers at the LF of the engine match the VIN of the car it came out of. If it does, it's the original 307. www.442.com has a FAQ section that should have info on ID'ing a 307.

I think a truck will work a 307 to death. Sounds like you have an old diesel pickup with a BOP transmission.

[Sgt Art]

5.0L is a 307 as Olds didn't make a 305, Chevy did. If it's an Olds engine, it's easy to identify by the oil filler spout that sticks up in front of the engine. Only Olds engines had this most excellent feature. Here's the casting numbers for Olds small bocks:

ID/ Casting

Code Year(s) CID Number Notes

1 '64-'66 330 381917 45° cam bank angle.

1A 330 381917 45° cam bank angle.

2 '68-'76 350 381917

2 '68-'70 350 395558

3 '66-'67 330 394417 39° cam bank angle.

4

5 '73,'74 350 395558

2A '75-'81 260 Solid main webs for 2A's only? At least for '76.

2B ??-'81 260 557751 Windowed main webs. Windowed main webs for 2B's only?

3A '79 350

3B '77-'80 350 557752

4A '77 403 557265 Solid main webs possibly

553990 for these three

554990 casting numbers.

4B '77-'79 403 557265 Windowed main webs always.

?? '85 307 556607

5A '81- 307 3161

D3 350 7582 Diesel

Some blocks, before 1977, have their ID cast above the right hand center freeze plug, eg. D for 425, F for 455. Olds didn't cast the displacement into the side of the blocks until they went to the light weight design in 1977. The 1977 and newer blocks will have the cubic inches cast in large raised numbers right above the right hand center freeze plug, eg. 403. The 307 will be in liters (5L), and a diesel engine will have the letters "DX" on it. The engine VIN letter will also be cast into the side of the block. Note that the 260 blocks sometimes have the last 3 digits of the casting number cast there, "355", which is rather misleading.

1968-later V-8 Engine

Have the last six digits of the VIN number, the year of the block, and the assembly plant stamped on the driver's side of the block below the cylinder head. A 2-letter code on the oil filler tube identified the engine.

You can use the VIN derivative number to ID the year. For 1968 and up blocks, this number is located on a pad just below the cylinder head on the front left side of the engine. This number will be stamped on a machined pad on the front driver's side of the block, just below the deck surface. Typically it will be covered with a power steering bracket or something, below the number one spark plug location.

This number should take the form of "35Mxxxxxx" where: 3 = Oldsmobile division.

5 = year of manufacture (8=68, 9=69, 0=70, ..., 4=74, 5=75, 6=76, etc.).

M = location of manufacture (M = Lansing, B=Baltimore, X = Kansas City, Z = Fremont, CA, etc).

xxxxxx = last six digits of VIN of car that motor originally came in (original car's sequential production number).

The letter indicating factory must match the letter in the sixth position of the car's VIN (it should also, of course, match the factory indication on the body data plate - in other words, for a Lansing-built car, the sixth place in the VIN would be an "M", the body data plate should indicate "LAN", and the third place in the engine ID should also be an "M").

The oil filler tube is stamped with a number that indicates the year and engine unit number. So, 2724927 would break down as follows: 2 = 1972.

724927 = engine unit number.

In 1980, VIN codes used a letter for the year designation, in the 8th character from the right (end of the VIN). Example: A=1980, B=1981, E=1984. I believe the number you posted 3EM266131 decodes:

3= Olds Division, E=1984 (year it was made) M=Lansing Plant 266131 is the last six of the VIN from which the engine originally came. As you indicated it's been rebuilt, I'm guessing someone probably replaced the engine in your 1980, 98 (which might have been a diesel when it left the factory - a lot of those were done around here).

P.S. A 260, 307, 350, and 403 are all small blocks. THe starter from the 350 should work on the 307 or 403. It might be a diesel engine (350) starter which were bigger.