identifying specs of a rebuilt engine

[Jride]

Hi there. Own a 1986 CJ7 Laredo . The engine is not original, and was taken from another CJ7 , by original owner. It's clearly a straight 6-cylinder, but how can i determine the other specs? Is it a AMC 258 i6 / 4.2l ? Something else?

Is there a way to determine the specs by looking at it?

thx for the help!

 

[Scout1067]

I am sure someone will correct me if I am wrong but if I understand it correctly the big difference between the AMC 258 i6 / 4.2l and 4.0 is different heads

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[Peanut Butter]

There is a number on the engine block that will identify the block (machined area near distributor). The head can be identified usually by a number or the way it looks. 4.0 L heads have several differences to them from a stock 242 or AMC 258 i6 / 4.2l head. Post a couple of pictures here. That will help with the head. Here is the block number information: https://www.jeepforum.com/forum/f8/identify-your-engine-1383352/

These parts also have serial numbers. Sometimes you can match up these numbers the the different components. In you case since you know that it is from a different Jeep, that doesn't help much. Here is a thread I worte on mine: https://www.jeep-cj.com/forums/f49/your-cj-original-maybe-not-heavy-pictures-25934/

 

[Jride]

thanks for the quick response. this community is awesome!

Found a bunch of numbers etched into the engine. the one that's most relevant, i think, is on the passenger side of the engine by the distributor. It's 910 04 — but there's an elevated 4 after the 910 (as if it's suppose to read 910 to the 4th power).

 

[Jride]

and here are some photos of the engine with random numbers i found etched into it.

 

[Peanut Butter]

The number etched into the block near the distributor indicates the year, month, size, and day the block was built. Based on the link I gave you, it was built 4 October, 1976 and is a ??. I cannot read the letter between the 910 and the 04 in your picture. Most likely a "C" which is a AMC 258 i6 / 4.2l ci 2 bbl. The other numbers are casting number for the manifolds. On the manifold side of the engine near the motor mount should be the casting number for the block. This number can also be looked up in the link I posted. The head looks to be the correct head for the engine. It has the steel valve cover. Also appears to be stock parts with it. (Distributor, manifolds, etc.) The only for sure way to tell if the engine was rebuilt with oversize pistons, etc. it to tare it apart and measure. There are a lot of things you can do to improve it's performance without a total rebuild. Electrical would be the first, then carburetor. Lot of good articles on this forum about this. Enjoy your new Jeep!