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ANOTHER Rockridge4wd Creation!! Spare Tire Carrier Delete The Jeep Forum Discount is ON!The Original 3/8" Ruffstuff Diff Cover!

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Unread 07-14-2015, 02:03 PM   #1
jcrocket13
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Identifying Engine

Hello all--

I've got an '87 YJ out in the yard. It has a rebuilt 4.2 engine in it, #212C21, which tells me it came off the line on Dec 21, 1972. Here's my problem. I want to put a new valve cover gasket on it, so I bought one for a '72 Wrangler. Doesn't fit. Since the 4.2, as far as I know, didn't go into Jeeps until 79(?), this must have come out of a Gremlin, Matador or another long forgotten AMC of the time. How can I find out which one and get the right gasket? Sure, I can cut my own, and I might, but I sure would be nice to know where the thing started its life in case I find any other small differences.

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Unread 07-14-2015, 02:22 PM   #2
Jeepsr4me
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have you tried to get one that is the year of the jeep?

I dont trust those numbers on the side....
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Unread 07-14-2015, 02:25 PM   #3
Jeepsr4me
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and it could be a 82... and I am pretty sure it is a 82


The engine Build Date Code is located on a machine surface on the right side of the cylinder block between the # 2 and # 3 cylinders. The numbers of the code identify the year, month and day that the engine was build.
Explanation Engine Build Date Code
Example: 3 10 C 11
1st Number Character is the build year: 3 = 1983, 4 = 1984
2nd and 3rd Number Characters is the build month: 01 = January, 12 = December
4th Letter Character code indicates the engine: C = 258 CID / 2v Carburetor / 9.2:1 Compression Ratio
5th and 6th Number Characters is the build day: 01, 02, 03 up to 31.
The example code 3 10 C 11 translate to: 258 CID (4.2 Liter) engine with 2V Carburetor and a 9.2:1 Compression Ratio, built on October 11, 1983.
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Unread 07-14-2015, 02:43 PM   #4
jcrocket13
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The numbers come off the block. If it's an '82, ok. But is there a difference in the cylinder head? I'm assuming what's under the head is the same. The gasket for the '87 doesn't fit.
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Unread 07-14-2015, 02:55 PM   #5
jcrocket13
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Also, it appears that whoever did the rebuild (and I think it was a sloppy job) had a problem getting a gasket because they used what looks like Form a Gasket #1 instead. This is just weird.
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Unread 07-14-2015, 03:11 PM   #6
Jeepsr4me
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take a pic and post up... It could be a 4.0 head.
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Unread 07-14-2015, 03:40 PM   #7
jcrocket13
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I'll get a picture up tomorrow. Raining now. Are the 4.2 and 4.0 heads interchangeable?
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Unread 07-14-2015, 04:35 PM   #8
Jeepsr4me
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no they are not... But people do it all the time...

Takes a little work but then you can do the EFI deal..


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Unread 07-14-2015, 04:44 PM   #9
jcrocket13
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Interesting. What are the things I should look for in comparing the 4.0 to the 4.2 head? I've called up images of the valve cover gaskets and they look identical, but I don't trust those images.
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Unread 07-15-2015, 04:15 AM   #10
Drednot
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How many holes are there for the valve cover?


The first year for the 258 (4.2L) in the CJ was 1972. But I agree, its most likely an '82


This is a '74...


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Unread 07-15-2015, 06:53 AM   #11
jcrocket13
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Well, here's the valve cover. Any idea what I'm dealing with here? Maybe I should give a prize for the right answer.
valve-cover.jpg  
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Unread 07-15-2015, 07:09 AM   #12
Jeepsr4me
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Damn dude, you a professional potog? That is the best cover pic I ever seen.
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Unread 07-15-2015, 07:19 AM   #13
jcrocket13
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Photography has been a hobby since I was a punk kid. Normally I do film, but digital is handy.

Oh, and this engine doesn't have a belt tensioner. Does that mean anything?
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Unread 07-15-2015, 07:58 AM   #14
1949er
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Plastic V/C they started using in the early 80tys ( 81 ? ) till early 87 , prone to breaking and leaking
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Unread 07-15-2015, 08:31 AM   #15
jcrocket13
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Leaking, yes. That's why I want rid of it. That's why I pulled it. I'm really in the process of putting in a new distributor, but I'm doing a few other things along the way. Before I go any further I want to make absolutely certain what engine I'm dealing with. The code on the block identifies it as clearly a 4.2. The problems with the valve cover gasket are weird. It was reputedly rebuilt with a larger cam, but I can't see that changing anything else.

So what you think? 4.0 or 4.2 cylinder head?

Last edited by jcrocket13; 07-15-2015 at 08:58 AM..
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