Identifying your 4.2L engine (2023 Update)

Umm... Bill yours is a 76-89 258 2bbl carb engine....

That is what the 'C' means.

The '0' means 1980.

Mike

William Oliveri wrote:

You are the one that posted the freaking link Bill!

Did you not read it?

I did.

And no 'C' does 'not' stand for carb.

Mike

William Oliveri wrote:

I stand corrected. C does not stand for carb and it does say the dates run to 89.

C- 258 2 bbl (4.2L, 76-89)

However, every site I've looked at similar to this one:

Go to this site

Take a look at these sites:

Bill

They warned about that on the first link Bill.

Some of the numbers went on when it was made and some went on for the actual model year it was sold as or built for.

Here is a quote:

An important thing to remember about AMC engines is that changes were made on a calendar year basis, not model year. The engine plant ran on its own schedule! This is why some 1980 model vehicles have the "heavy"

Mike

William Oliveri wrote:

Do you have a plastic valve cover?

Do you know what this means? Heavy 258 and Light 258?

What would really help is to totally exclude 1990 year engines. I need to find out what the date code stamp is for a 1990 258.

My situation is a little different. The previous owner had the short block replaced due to him pouring water on a over heated engine. I have all the receipts. He had the head serviced for over 1000.00 and replaced the short block with a used one for over 2000.00.

This was in 1997 on a 83 CJ7. If the shop replaced the short block with an

I know I have 1/2" head bolts and not 7/16" but that doesn't help either because 80 and 90 year blocks have 1/2" head bolts.

Bill

You can't have a 90, the cranks are different and the transmission will not bolt up to it without some serious machining or searching for parts.

They changed to the YJ setup in 87.

They used 2 engine blocks for the 1980 year. You got the later one or the 444 cast.

That does not mean you got a 1980 'engine', just a block from that year. The crank could be any up to 86.

If this is a built up short block, then the engine cast just came out of a pile they had around the shop and they put a CJ crank in it.

All bets are off when talking built engines, nothing has to match up 'properly' and a block is basically a block.

Not likely the fool paid $2000.00 for a 'used' short block, that is a really expensive rebuilt one's price.

Emissions look at the heads and exterior junk.

Mike

William Oliveri wrote:

Wow, Ok. Even though the receipts do not state "rebuild" but "replaced" with a used engine, I am hopeful you are correct.

Thanks Mike. That helps a lot.

Bill

One way to tell 'maybe' is by just looking close at the oil pan gasket or timing cover for RTV or gasket maker.

When someone installs a used engine, they don't mess with those covers usually. Your compression is also correct for a 'new' engine.

A used 258 short block goes for a couple hundred dollars, not a couple thousand....

Mike

William Oliveri wrote:

There's no "short" version of the AMC 258.

A grand for the head, eh? I just looked at my checkbook: $187.09US to have my 258 head hot-tanked, the valves ground and new seals installed at a local speed shop. While it was there they made a pass through the planer just to be sure it wasn't warped and backed out a broken stud for me.

Two grand to have a shop R/R an engine doesn't surprise me, though.

It goes by smog system, not individual parts, no?

I have a 1990 258 (now with a Weber carb.). Is there anyway I can lookup some info. for you guys to solve this mystery?

Yeah, that'd be great. Look on the passenger side of the engine just below the #3 and #2 spark plug holes on the block. There should be a flat plate there with some numbers and letters on it.

What does it say?

Thanks,

Bill

Correct me if I'm wrong but the term "short block" is referring to the engine without the head. "Long Block" would be referring to the engine with the head.

I'll scan the receipts in tomorrow up to my web page for reference. He also had the carb rebuilt by Chrysler which was also big bucks.

1990 Jeep Wranger YJ w/ 258

So, 1990 year model w/ a 1986 block?

The C is close enough in stating that it is a "C- 258 2 bbl (4.2L, 76-89)", but the "L" baffles me.

Anyone have a clue as to the "L" portion of the designation? The website info. for the "L" doesn't make sense in this case.

When ordering parts, I usually tell the parts flunkies behind the counters it's an 1989....I'll normally get the parts right that way since if I tell them it's a 1990, they screw up more often.

This number is in a different format than the web site states. Looks like the format changes in 1990 otherwise your number would be:

Year 1990 Month 63 Day Built 06

Doesn't fit the following format:

1. Year built code

1. Engine size/type code

However, this information does confirm Mike's position which is now very clear.

It could be that the day code letters are two letter codes rather than the single letter codes the CJs have but that's just guessing.

Bill

1990 Jeep Wranger YJ w/ 258

So, 1990 year model w/ a 1986 block?

The C is close enough in stating that it is a "C- 258 2 bbl (4.2L, 76-89)", but the "L" baffles me.

Anyone have a clue as to the "L" portion of the designation? The website info. for the "L" doesn't make sense in this case.

When ordering parts, I usually tell the parts flunkies behind the counters it's an 1989....I'll normally get the parts right that way since if I tell them it's a 1990, they screw up more often.

bill-here's some more info about the engine- Oversize or undersize components look between the ignition coil and the distributor. there may be a couple of letters stamped on a boss. here are the codes:

B - All cylinder bores (0.254mm (0.010") oversize) M - All crankshaft main bearing journals (0.254mm (0.010") oversize) P - All connecting rod bearing journals (0.254mm (0.010") oversize) C - All camshaft bearing bores (0.254mm (0.010") oversize)

Example: if you see the letters "PM" you have crankshaft bearing journals and connecting rod journals that are undersize.

this info is out of my factory manual-if you can afford them ($100 in 1998), get a copy of it. it has sooo much info on everything on your car.

Thanks Serg,

Yeah, the FSM I have is the first thing I checked but it was not very telling that year I guess. Probably gets better as the years go by.

Thanks for the info.

Bill