Mopar A / Poly Small Block Torque Specs

Intro

The A / Poly small block is not an LA engine wearing antique valve covers. Chrysler may have used familiar displacement numbers on both sides of the family change, but a Poly 318 did not wake up one morning and become the later LA 318 because somebody recognized the badge.

The 277, 301, 303, 313, 318, and 326 belong to Chrysler’s earlier A-block Poly family. Their canted-valve heads, rocker shafts, intake arrangement, exhaust hardware, front-cover pieces, and water-pump installation give the wrench a different job from the later LA engine that eventually replaced them.

This chart also contains several places where identifying the actual bolt matters more than remembering the engine family. The rocker-shaft hardware uses only 17-20 lb-ft. Converter bolts split sharply between 25 and 65 lb-ft depending on whether the bolt is 5/16 or 7/16 inch. Some exhaust, water-pump, and front-cover fasteners may enter coolant or oil-path areas and need sealer as well as torque.

Old Mopar does not mean crude Mopar. The engine expects the mechanic to know which family, which bolt, and which hole is in front of the wrench.

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General Torque Specs

¹ Thin covers, pans, carburetor flanges, and cork-style gaskets distort easily. Tighten evenly and do not turn seep control into bent metal.

² Use the correct tightening sequence and bring the fasteners up in stages. A good number used in a dumb pattern is still dumb.

³ Poly rocker-shaft hardware uses a low value. Do not treat it like main-cap hardware.

⁴ Some lower-row exhaust fasteners may enter coolant. Seal the right fasteners instead of pretending dry threads and optimism are the same thing.

⁵ 5/16 in. converter bolts.

⁶ 7/16 in. converter bolts.

⁷ Water-pump and front-cover bolts may enter coolant or oil-path areas depending on layout. Seal the right fasteners.

The converter rows are where ‘converter bolt’ proves it is not an identification. A 5/16-inch bolt gets 25 lb-ft. A 7/16-inch bolt gets 65. Same job description, very different bolt, and a 40 lb-ft gap wide enough to make guessing an expensive hobby.

The rocker shafts live at the opposite end of the enthusiasm scale. Their 17-20 lb-ft range is low because nothing up there is a main cap wearing a disguise. Letting big-block muscle memory pick the number is a very efficient way to damage small hardware.

The head and intake numbers come with a procedure attached. Sequence and stages are part of the specification, not optional scenery around it. Eighty-five pounds on a head bolt does not become good work just because the wrench clicked after the pattern was ignored.

Then there are the fasteners that may open into coolant or oil-path areas. Exhaust, water-pump, and front-cover bolts can require sealant depending on location. Torque controls clamp load; it has never learned how to plug a wet thread.

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Important Notes

• A Poly 318 and an LA 318 share a displacement number, not an instruction sheet. The heads, intake, rocker gear, covers, and front hardware do not care that both badges match.
• The canted-valve Poly heads give the top end its own layout. Intake and exhaust pieces should be identified as Poly parts instead of being chosen from later small-block memory.
• Rocker-shaft bolts use only 17-20 lb-ft. That low number is deliberate. The shaft assembly does not become stronger when somebody treats it like a main cap.
• Converter-bolt diameter decides whether the chart says 25 or 65 lb-ft. Measure the bolt before choosing the number; ‘converter bolt’ is a job title, not an identification.
• Some lower exhaust bolts and some water-pump or timing-cover fasteners may communicate with coolant or oil-path areas. The right torque on unsealed wet threads can still leave a leak.
• Valve covers, pans, and carburetor flanges are thin enough to lose the argument with the wrench. Once the rail bends around a bolt hole, more torque merely makes the sealing surface worse.

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Common Mistakes

• Seeing “318” and reaching for LA small-block numbers without first determining whether the engine is an early Poly or the later LA design.
• Using a heavier familiar Mopar setting on the 17-20 lb-ft rocker-shaft bolts because the correct Poly number looks too small to somebody accustomed to larger hardware.
• Applying the 25 lb-ft converter value to a 7/16-inch bolt, or the 65 lb-ft value to a 5/16-inch bolt, because bolt diameter never entered the conversation.
• Installing an exhaust, water-pump, or front-cover fastener dry after removing one that came out wet. A torque specification is not thread sealer.
• Ignoring tightening sequence on the heads or intake and assuming the final torque number will somehow straighten out an uneven clamping job.
• Trying to stop a valve-cover, oil-pan, or carburetor leak with more wrench after the flange has already bent around the fastener.

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Bottom Line

The A / Poly family came before the LA and carried its own ideas about heads, rocker gear, manifolds, front covers, and hardware. The later small block did not erase any of them.

The chart proves it in places that can hurt expensive old parts: 17-20 lb-ft rocker bolts, converter bolts that jump from 25 to 65 depending on diameter, thin covers that want restraint, and front-end fasteners that may need sealant because the hole behind them is wet.

Identify the Poly first. Then identify the bolt. A familiar displacement number can sit on the air cleaner and look helpful; it still cannot tell the wrench which engine is actually on the stand.

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Related Links

Engine Specs

• Mopar A / Poly 277 V8 Engine Specs
• Mopar A / Poly 301 V8 Engine Specs
• Mopar A / Poly 303 V8 Engine Specs
• Mopar A / Poly 313 V8 Engine Specs
• Mopar A / Poly 318 V8 Engine Specs
• Mopar A / Poly 326 V8 Engine Specs

Engine Family

• Mopar A / Poly Small-Block V8 Engine Family

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