Jeep CJ/Scrambler 1971-1986 Repair Guide

Engine

Print

See Figures 1, 2 and 3

4-134

The engine serial number for the Kaiser/Willys built F-Head 4-cylinder engine is located on the water pump boss at the front of the engine. It consists of a 5 or 6 digit number. The engine code prefix for the F-Head is 4J.

It is sometimes necessary to machine oversize or undersize clearances for cylinder blocks and crankshafts. If your engine is equipped with oversized or undersized parts, it is necessary to order parts that will match the old parts. To find out if your engine is one with odd-sized parts, check the engine code letter or the engine code number itself-which in some cases is followed by a letter or a series of letters. The following chart explains just what the letters indicate:



Letter A (10001-A) indicates 0.010 in. (0.25mm) undersized main and connecting rod bearings.
 
Letter B (10001-B) indicates 0.010 in. (0.25mm) oversized cylinder bore.
 
Letter AB (l0001-AB) indicates the combination of A and B above.
 
Letter C (10001-C) indicates 0.002 in. (0.051mm) undersized piston pin.
 
Letter D (10001-D) indicates 0.010 in. (0.25mm) undersized main bearing journals.
 
Letter E (10001-E) indicates 0.010 in. (0.25mm) undersized connecting rod bearing journals.
 

4-150

The engine serial number for the American Motors built 4-150 is located on a machined pad at the rear right side of the block, just below the head.

Also on the block, just above the oil filter, is the oversized/undersized component code. The codes are explained as follows:



Letter B: cylinder bores 0.010 in. (0.25mm) over
 
Letter C: camshaft bearing bores 0.010 in. (0.25mm)over
 
Letter M: main bearing journals 0.010 in. (0.25mm)under
 
Letter P: connecting rod journals 0.010 in. (0.25mm) under
 



Click image to see an enlarged view

Fig. Fig. 1: Engine number location for the 4-150 engine



Click image to see an enlarged view

Fig. Fig. 2: Oversized/undersized engine component code location on the 4-150



Click image to see an enlarged view

Fig. Fig. 3: 1980-83 engine ID number, 4-150 engine

4-151

In 1980, a General Motors 151 cid, 4-cylinder engine became standard equipment on all CJ models. A three character code is stamped into the left rear top corner of the block. Additionally, engines built for sale in Georgia and Tennessee have a non-repeating number stamped into the left rear block flange.

6-225

The engine number for the Buick built V6-225 engine is located on the right side of the engine, on the crankcase, just below the head. The code is KLH.

It is sometimes necessary to machine oversize or undersize clearances for cylinder blocks and crankshafts. If your engine is equipped with oversized or undersized parts, it is necessary to order parts that will match the old parts. To find out if your engine is one with odd-sized parts, check the engine code letter or the engine code number itself-which in some cases is followed by a letter or a series of letters. The following chart explains just what the letters indicate:



Letter A (10001-A) indicates 0.010 in. (0.25mm) undersized main and connecting rod bearings.
 
Letter B (10001-B) indicates 0.010 in. (0.25mm) oversized cylinder bore.
 
Letter AB (10001-AB) indicates the combination of A and B above.
 
Letter C (10001-C) indicates 0.002 in. (0.051mm) undersized piston pin.
 
Letter D (10001-D) indicates 0.010 in. (0.25mm) undersized main bearing journals.
 
Letter E (10001-E) indicates 0.010 in. (0.25mm) undersized connecting rod bearing journals.
 

6-232 and 6-258

The engine code is found in the identification plate on the firewall. The second location is on a machined surface of the block between number 2 and 3 spark plugs. For further identification, the displacement is cast into the side of the block. The letter in the code identifies the engine by displacement (cu. in.), carburetor type and compression ratio.

All of the engines have the same undersize/oversize letter codes, located on the boss directly above the oil filter. The parts size code is as follows:



Letter B indicates 0.010 in. (0.25mm) oversized cylinder bore.
 
Letter M indicates 0.010 in. (0.25mm) undersized main bearings.
 
Letter P indicates 0.010 in. (0.25mm) undersized connecting rod bearings.
 
Letter C indicates 0.010 in. (0.25mm) oversized camshaft block bores.
 

8-304

On the American Motors built 8-304 engines, the number is located on a tag attached to the right valve cover. For further identification, the displacement is cast into the side of the block. The letter in the code identifies the engine by displacement (cu. in.), carburetor type and compression ratio.

All of the engines made after 1971 have the same undersize/oversize letter codes, located on a tag next to the engine number. The parts size code is as follows:



Letter B indicates 0.010 in. (0.25mm) oversized cylinder bore.
 
Letter M indicates 0.010 in. (0.25mm) undersized main bearings.
 
Letter P indicates 0.010 in. (0.25mm) undersized connecting rod bearings.
 
Letters PM indicate a combination of the above specifications for P and M.
 
Letter C indicates 0.010 in. (0.25mm) oversized camshaft block bores.
 

 
label.common.footer.alt.autozoneLogo