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Main stud / bolt installation

This main cap fastener kit is supplied to fit Ford Y-Block engines. On B9AE, C1AE and C2AE blocks there are likely sufficient threads in the block for the fasteners. If the block casting number is an “E” series, such as ECG, ECK, ECZ, EDB, the depth of the threads must be increased. If using a block with sufficient threads skip to the installation directions.

Why is this modification necessary?

All Y-Blocks built prior to mid 1959 had main cap bolts that were too short to satisfactorily retain the main caps under high performance usage. This is especially true for the 312 blocks.  All 1954 to March 1959 blocks had insufficient threads in the block to accept longer fasteners.

Drilling the block for studs or bolts

·         In all cases the threads at the block end of the stud are 1-1/4” long. This requires drilling the main cap bolt holes to a depth of 1.350” - 1.400” with a 27/64” drill bit. Do not exceed this depth as the oil passage can be opened to the sump. This is best accomplished on a mill or large drill press.

·         Tap the holes with a 1/2” X 13 tpi bottoming tap.

·         On the oil filter side of the block the oil passage will be encountered. This is not a problem as all production blocks after mid 1959 were drilled to this depth.


·         After removing all chips from the machining process thread the studs into the block.

·         Unthreaded portion of stud should seat on the block.

·         If working on a 239-256-272 or 292 all fasteners should be the same length. On 312 blocks main caps #1- #4 are taller and require longer fasteners than #5. Install the 2 short bolts in #5

·         On the oil filter side of the engine check to see if the stud is blocking the oil passage. The threads often need to be shortened to 1-1/8”. If the stud is ground to shorten, cool the part frequently to avoid excess heating. The end can be ground to a shallow “V” to allow oil to pass without excessive grinding.

·         Why aren’t studs with 1-1/8” threads supplied? ARP doesn’t make them!

·         Thread length is not a problem on the starter side of the block.

·         The aluminum rear main seal retainer must be notched to clear the main cap nuts.

·         Install all studs hand tight. Install main caps, washers and nuts. Install rear main seal retainer to ensure proper fit. Set the oil pan on the block and check for clearance at the #5 studs and nuts.

·         If studs for rear (#5) main cap must be shortened, leave as much thread exposed above the nut as possible. There can be interference with front sump oil pans. MAIN CAP STUDS ONLY: Torque stud nuts to120# with 30wt. oil on threads.

·         MAIN CAP BOLTS ONLY: place washer on bolt with internal bevel toward bolt head. Torque to 110-120# with oil on threads and under head of bolt.

·         After installation of the studs and main caps, linehone the block to the median dimension. All blocks except 312 are 2.6916”.           312 only is 2.8164”.

·         During assemble torque main cap fasteners to the same figure used during line honing.

·         The rear main seal retainer must be notched to clear the #5 main cap nuts if using studs

·         Some passenger car front sump oil pans will need to be dimpled to clear #5 main stud nuts


Your block is now capable of withstanding high performance usage.