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Unread 04-07-2013, 06:53 PM   #1
EgulAye
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1980 CJ5 
 
Join Date: Mar 2013
Location: Mechanic Falls, Maine
Posts: 492
What is a low compression 258? (Answer unclear, but issue resolved)

I just picked up a second 1980 CJ5. My first one has major frame issues and I needed a better platform to work with. Both have the straight six 258, 4-speed manual transmission, D300 transfer case, etc. (This new Jeep has a 3-speed in it, but it's pretty obvious it came with a 4-speed)

The new CJ has a one barrel carburetor on it instead of the Carter BBD. Also, the engine code is a B, which doesn't show up on the VIN decoder charts. That engine code appears pre-76 as a 258 low comp., but I have not been able to find anything that says what that is or what the implications are.

Is there something different about the motor or is it just the carburetor? Any info or leads on where to look would be much appreciated.

Thanks,

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Unread 04-08-2013, 08:50 AM   #2
1986cj
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1986 CJ7 
 
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Only thing I have says that from
B- 258 1 bbl Low Compression (71-74, Jeep ONLY)
The 258 used in '72-'78 CJs, J-series pickups, and Wagoneers, some used a 1bbl carb

and lower compression than later 258s.

AMC 258 I6

Bore x Stroke 3.75" x 3.90"

Displacement 258 (4.2L)

Compression Ratio 8.0:1

Horsepower (net) 110@3500

Torque (net) 195@2000

Main Bearings 7

Valve Configuration OHV

Fuel 1bbl
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Unread 10-17-2013, 06:56 PM   #3
EgulAye
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Looking at other sources for the VIN information today I realized that engine code B means my jeep originally came with the GM-151 "Iron Duke" and the SR5 four speed transmission. Wikipedia had the answer.
Code:
From 1980 to 1983, the CJ-5 came standard with a "Hurricane"-branded 
version of the GM Iron Duke I4 with an SR4 close-ratio four-speed manual transmission.
Looking at this Engine Code web page again I see that
Code:
B- 151 2 bbl (80-83, GM 2.5L)
is what my VIN indicates. This option isn't listed in my Chilton's manual, even though the Wikipedia article says it was the standard option.

Of course, I've also determined that my engine in a 1978 232 with the 1bbl Carter YF carb. Someone in the past must have been tired of the four cylinder, or it failed. The transmission was probably changed to the T150 three speed at the same time. The 232 and the 3-speed were standard options from '78 and they probably came together.
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