Rebuilding Your 355 Small Block Chevy: A UK Guide

Embarking on the journey of rebuilding a 355 Small Block Chevy engine is a truly rewarding endeavour for any automotive enthusiast. It's a process that demands precision, patience, and a keen eye for detail, but the satisfaction of bringing a venerable powerplant back to life is unparalleled. The 355 SBC, a popular choice for its robust design and ample aftermarket support, offers a fantastic platform for learning the intricacies of internal combustion engines. This guide will walk you through the essential steps, ensuring your rebuild is thorough and successful, ready to deliver reliable performance for years to come.

Before you even think about assembly, the foundation of a successful rebuild lies in meticulous preparation. This involves thorough cleaning, inspection, and often, machining of the core components. Assuming your block and crankshaft have been professionally checked and machined to specification (e.g., bored, honed, crankshaft ground), you're ready to begin the assembly phase.

The Foundation: Block Preparation and Bearing Installation

Your engine block must be scrupulously clean, with all oil passages and bolt holes free of debris. Use compressed air to blow out all channels and ensure no machining swarf remains. This cleanliness is paramount to prevent premature wear.

Main Bearing Installation

Begin by installing the main bearings into the block and main caps. These are typically two-piece bearings; ensure the correct halves are placed in the block and caps, aligning the tangs with the notches. Apply a thin coat of assembly lube to the bearing surfaces. The thrust bearing, which controls crankshaft end play, is usually a specific main bearing (often the centre one on a small block Chevy) and must be oriented correctly.

Crankshaft Installation and Clearances

Carefully lower the crankshaft into place, ensuring it seats properly on the main bearings. Before torquing the main caps, double-check that the thrust bearing is correctly seated. Apply assembly lube to the main journal surfaces. Install the main caps, ensuring they are oriented correctly (usually marked with numbers or arrows). Torque the main cap bolts to the manufacturer's specified torque settings in the correct sequence. It’s crucial to use a torque wrench for this and all critical fasteners. Once torqued, rotate the crankshaft a few revolutions by hand to check for any binding. It should turn smoothly with consistent resistance.

The Heart of the Engine: Camshaft and Timing

The camshaft dictates the engine's breathing, controlling valve lift and duration. Its proper installation is critical.

Camshaft Installation

Liberally coat the camshaft lobes and journals with a dedicated cam assembly lube. Carefully insert the camshaft into its bearings at the front of the block. As you insert it, gently rotate the camshaft clockwise. This helps to align the cam journals with the bearings and prevents damage. Continue rotating and pushing until the camshaft is fully seated. Once installed, rotate the crankshaft again for a few revolutions to confirm that there is no interference between the crankshaft counterweights and the camshaft. This is a vital check, especially if using a high-lift camshaft or a non-standard crankshaft. Once all is clear, stop rotating the crankshaft at the point where the front-left cylinder (cylinder #1) is at Top Dead Centre (TDC) on its compression stroke. This means both valves for cylinder #1 are closed and the piston is at the very top of its travel. This position is critical for timing.

Oil Pump Installation

Now, fit the oil pump. The oil pump typically attaches to a port at the rear of the small block, driven by a shaft from the distributor gear. Ensure the oil pump drive shaft engages correctly with the pump and the distributor drive in the block. Secure the oil pump with its bolts, often using a new gasket if applicable.

Timing Gears and Chain

With cylinder #1 at TDC, it's time to install the timing components. Attach the bottom timing gear to the crankshaft snout, aligning its keyway with the crankshaft key. Then, attach the top timing gear to the camshaft nose. The most crucial step here is to align the timing marks on both gears precisely. These marks typically face each other or align with specific points on the block, depending on the manufacturer. Slide the timing chain over both gears simultaneously, maintaining the alignment of the marks. This ensures the camshaft and crankshaft are synchronised, allowing the valves to open and close at the correct time relative to piston movement.

Timing Chain Cover, Oil Pan, and Seals

Once the timing chain is correctly installed and aligned, fit the timing chain cover into place. Apply a bead of RTV sealant or use a new gasket around the mating surfaces, ensuring the front crankshaft seal is properly seated in the cover. Bolt it on, torquing the bolts evenly. Next, attach the oil pan. Before doing so, ensure both the front and rear crankshaft seals are correctly fitted. The front seal is in the timing cover, and the rear seal is in the block and main cap assembly. Use a new oil pan gasket and apply RTV sealant at the corners where the timing cover and rear main seal retainer meet the block. Carefully position the oil pan and secure it with its bolts, again using a torque wrench.

Pistons, Rods, and Top End Assembly

With the rotating assembly mostly complete, attention turns to the pistons and cylinder heads.

Piston and Connecting Rod Assembly

If not already assembled, install the piston rings onto the pistons, paying close attention to their orientation (top, second, and oil rings) and gap staggering. Apply assembly lube to the piston skirts and ring lands. Install the connecting rod bearings into the connecting rods and caps, again lubricating them. Carefully insert the piston and connecting rod assemblies into their respective cylinders from the top, using a piston ring compressor to guide the rings. Ensure the piston and rod orientation is correct; most pistons have a mark (e.g., an arrow or dot) indicating the front, and connecting rods are often offset or marked for specific cylinder banks.

Once the piston is in, guide the connecting rod onto the crankshaft journal. Install the connecting rod cap, ensuring its orientation matches the rod. Apply assembly lube to the rod bearing surfaces. Torque the connecting rod bolts to specification. Repeat this process for all eight pistons.

Cylinder Head Installation

Before installing the cylinder heads, ensure the block deck and cylinder head surfaces are perfectly clean and flat. Place new cylinder head gaskets onto the block, aligning them with the dowel pins. Carefully lower the cylinder heads onto the block. Install the cylinder head bolts, applying a thread sealant to those that enter water jackets. Torque the cylinder head bolts in the specified sequence and in stages, as per the manufacturer’s instructions. This is a critical step for head gasket sealing and preventing warpage.

Valvetrain Components

Install the pushrods into their bores, ensuring they seat properly in the lifters. Place the rocker arms onto their studs or pedestals, followed by the rocker arm nuts or bolts. Adjust valve lash according to the camshaft manufacturer's specifications. This can be a zero-lash adjustment for hydraulic lifters (plus a half to full turn) or a specific clearance for solid lifters. Take your time here to ensure proper valve operation.

Intake Manifold and External Components

Install the intake manifold, using new gaskets and a bead of RTV sealant at the front and rear china walls. Torque the intake manifold bolts in the correct sequence. Finally, install the remaining external components: water pump, exhaust manifolds, distributor (aligning the rotor with cylinder #1), spark plugs, and any accessories like the alternator and power steering pump. Double-check all fluid levels before attempting to start the engine.

Key Considerations for a Successful Rebuild

A successful engine rebuild isn't just about following steps; it's about understanding the nuances.

• Measure Everything: Before assembly, measure all clearances – main bearing, rod bearing, piston-to-bore, piston ring end gap, camshaft end play. These measurements confirm that machined parts are within specification and that you have selected the correct bearing sizes.
• Lubrication is Key: Use proper assembly lube on all rotating and sliding surfaces. This provides initial protection during the first few moments of engine operation before oil pressure builds.
• Torque Specifications: Always use a calibrated torque wrench for all critical fasteners. Over-tightening can stretch bolts and distort components; under-tightening can lead to loosening and failure.
• Cleanliness: We cannot stress this enough. Any dirt, grit, or metal shavings can cause catastrophic damage to freshly machined surfaces. Work in a clean environment.
• Patience: Do not rush the process. Take breaks if you feel frustrated or tired. A methodical approach will yield the best results.

Commonly Used Tools

Here’s a brief list of essential tools you'll need for an engine rebuild:

Frequently Asked Questions (FAQs)

How long does a 355 Small Block Chevy rebuild typically take?

The duration varies significantly based on your experience, the condition of the core components, and how much machining is required. For a first-timer working alone, it could take several weeks of dedicated effort, whereas an experienced mechanic might complete the assembly in a few days once all parts are ready.

What's the approximate cost of rebuilding a 355 SBC?

Costs can range widely. A basic rebuild with standard components might start from £1,500-£2,500 for parts and machining, but if you opt for high-performance components, extensive machining, or professional assembly, costs can easily exceed £5,000 or more. It's essential to get quotes for machining and price all your parts before starting.

Do I need special tools for an engine rebuild?

Yes, certain specialised tools are essential for accurate and safe assembly, such as torque wrenches, Plastigauge, micrometers, and a piston ring compressor. While you might be able to borrow some, owning them is recommended for any serious engine work.

Should I rebuild my old engine or buy a new crate engine?

This depends on your goals and budget. Rebuilding offers the satisfaction of doing it yourself, can be more cost-effective for a mild street engine, and allows for customisation. A crate engine offers a ready-to-install solution with a warranty, often quicker, but might be less personalised or more expensive initially.

What is the importance of engine break-in after a rebuild?

Proper engine break-in is crucial for the longevity of your newly rebuilt engine. It allows piston rings to seat correctly against the cylinder walls and ensures proper wear patterns for camshaft lobes and lifters (especially critical for flat-tappet cams). Follow the cam manufacturer's break-in procedure, which often involves running the engine at a specific RPM for a set period and then performing oil changes.

Rebuilding a 355 Small Block Chevy is more than just a mechanical task; it's an educational and deeply satisfying experience. By following these steps with diligence and attention to detail, you'll not only gain a deeper understanding of your engine but also enjoy the thrill of hearing your revitalised powerplant roar to life, ready for many more miles on the UK's roads.

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