Decoding the engine number

[Chukkklez]

I’ve read everywhere how to decode the engine number near the distributor, but my engine number doesn’t exactly seem to follow the same rules or maybe I’m overlooking something simple (Most likely the case), but the number stamped on mine is 707M13 and all I’m trying to do is see if it’s the numbers matching engine for my MJ so I can decide to build it or just find one in better shape and have my fun with that one. Any and all help is appreciated!

[eaglescout526]

Your engine was made in 1987 July 13th. M means all crank main bearing journals are 0.010 undersized

[Chukkklez]

You’re badass, thank you!

[eaglescout526]

No problem! Helps to have the actual engine service manual lol. 

[500 MJ]

@eaglescout526, can you decode another engine once I get you the numbers from it?

 

And - Is there any other way to determine if a driveline is all “numbers matching” to the chassis?

[eaglescout526]

13 minutes ago, 500 MJ said:

@eaglescout526, can you decode another engine once I get you the numbers from it?

 

And - Is there any other way to determine if a driveline is all “numbers matching” to the chassis?

Of course I can! Fun to do actually. 
 

Great question! The only way I have found to determine that is the build date on both the trans and engine. 

[86 mj]

@eaglescout526 i have a engine i d 605H12 2.5 in a 86 mj with the serpentine belt and tbi thank you 

[eaglescout526]

44 minutes ago, 86 mj said:

@eaglescout526 i have a engine i d 605H12 2.5 in a 86 mj with the serpentine belt and tbi thank you 

I will get it decoded for ya this evening!

[86 mj]

thanks

[eaglescout526]

7 hours ago, 86 mj said:

605H12

1986(6) May(05) 2.5L TBI(H) 12th day(12)

 

On the 2.5L there should be one or two more letters by the distributor, they will say what in the engine is to size like M above is Crankshaft Main bearing journals are .010" undersize.

[86 mj]

thank you for the info

[eaglescout526]

No problem!