Engine Rebuild: Cleaning and Machining

Embarking on an engine rebuild is a significant undertaking, and at its core lies the paramount importance of cleanliness and precision. The adage 'clean, clean, and then clean some more' isn't just a catchy phrase; it's the foundational principle that separates a successful rebuild from one plagued by premature failure. This guide will walk you through the essential steps of cleaning, preparing, and understanding the crucial machining processes involved in bringing your engine back to life.

DIY Cleaning and Preparation

Many components of your engine can be effectively cleaned and prepared by you, the enthusiast. This not only saves on costs but also allows for a more intimate understanding of your engine's condition. Items that do not have moving parts, such as valve covers, front and rear engine plates, lifter covers, timing covers, and distributor bases, are prime candidates for your own attention.

Scraping and Degreasing

Begin by meticulously scraping off as much old gasket material as possible. This initial step is crucial for ensuring a clean mating surface. Following this, move on to degreasing. While a dedicated parts washer is ideal, a makeshift solution can be created using a 5-gallon bucket and water-based degreasers. Always wear rubber gloves, as even water-based chemicals can be harsh on the skin. There's no need to rush this process; allowing the degreaser adequate time to work is key. In some instances, prolonged soaking can even strip away old paint, revealing bare metal.

Achieving Bare Metal

The aim for many builders is to get parts down to bare metal. Painting over old, unknown paint can lead to compatibility issues, where reactions between different paint formulations can cause wrinkling or adhesion problems. For achieving a bare metal finish, a bead blast cabinet is the most effective tool. However, if this isn't accessible, a wire brush attached to a drill or a bench grinder can also yield satisfactory results. Always wear eye protection during these abrasive processes.

Professional Machining: What to Expect

While you can handle much of the initial cleaning, certain vital internal components and larger parts necessitate the expertise and specialised equipment found in a professional machine shop. Taking your parts to a machine shop requires a clear plan and an understanding of your expectations. Don't assume they know precisely what you want; communicate your goals clearly.

Engine Block Preparation

The engine block is the heart of your engine, and its preparation is critical. A key step is checking the straightness of the block's deck surface, where the cylinder head attaches. If this surface is not perfectly flat, it must be resurfaced. It's acceptable if some areas around the water jacket don't completely clean up during decking; aggressive machining of these areas can remove more material than necessary. A word of caution: some engines, like the Spitfire and Midget 1500, and later TR6 models, have specific recesses around the cylinder bores. When decking these blocks, remove no more than .010" to ensure the head gasket can seal properly.

Piston-to-Cylinder Wall Clearance

Accurate piston-to-cylinder wall clearance is vital for performance and longevity. If the existing gap is too large, the cylinders will need to be bored out, and new, oversized pistons fitted. Discuss the required piston size with your machinist, who will measure the new pistons to ensure the correct bore size. After boring, the cylinders will be honed to achieve the proper surface finish for the piston rings. Finally, a machinist will use a specialised tool to chamfer the tops of the bores. This chamfering prevents the piston rings from catching and breaking during installation.

Line Boring and Cam Bearings

Line boring is typically not required for most street engine rebuilds. Its purpose is to ensure perfect alignment and sizing of all crankshaft journals. However, many British engines feature cam bearings within the block, and these should always be replaced. Full-circle cam bearings are generally preferred over the split type, and your machine shop will have the necessary tools and expertise. Crucially, bring the camshaft you intend to use to the shop so they can ensure a perfect fit with the new cam bearings, which may involve honing.

Crankshaft Machining

The crankshaft is subjected to immense forces and requires meticulous attention. Your car service shop should magnaflux your crankshaft to detect any hidden cracks. This process involves applying a fluid or powder to the crankshaft, which then highlights cracks when viewed under a black light. This procedure requires a trained eye to interpret the results accurately.

Crankshaft Measurement and Grinding

The crankshaft must be measured for wear and sizing. If it's out of specification and requires regrinding, various undersized crankshaft bearings are available. Crankshaft grinding is a highly skilled process. Seek out a machine shop with a strong reputation for this specific work; asking where racers go is often a good indicator. When a crankshaft is reground, it is extremely important that the fillet radius – the edges of the journal where it joins the crankshaft body – is properly restored. These areas are prone to cracking, making the correct fillet radius essential for the crankshaft's overall strength.

Connecting Rods

The big end of the connecting rods, which clamp around the crankshaft, must be checked for proper sizing. If your connecting rods use floating piston pins, the associated bushings will also need to be checked for play and wear. As a general rule, it's best to replace the rod bolts. Connecting rod big ends almost always warrant resizing, and this is considered a must if you are replacing the rod bolts. You may also need to replace the small end bushings on floating rod types.

Press-Fit Piston Pins

Some connecting rods use a press-fit for the piston pins. This type of assembly requires special tools for removing the old piston and installing the new ones, and is not a DIY task. Removing old pins is typically done through cold pressing. Installing new piston pins and pistons requires a rod heater, where the rod is heated to around 1200 degrees Fahrenheit, and then the piston and pin are quickly installed before the rod cools. This is unequivocally a job for a professional.

Flywheel Machining

If you can feel a lip or catch a fingernail on the flywheel's surface where the clutch disc rides, the flywheel will need resurfacing. Also, inspect the starter ring gear. If it shows signs of wear, it should be replaced. Your machine shop can easily perform both of these services.

Cylinder Head Overhaul

For most enthusiasts, delivering the complete cylinder head to a machine shop is the most practical approach. They can handle the disassembly, cleaning, crack detection, machining, and reassembly.

Valves, Guides, and Seats

Most cylinder head components are relatively inexpensive. Replacing valves and valve springs is highly recommended. Refacing valves is often discouraged; if the margin (the vertical part of the valve just below the sealing area) is ground away during refacing, it can leave a sharp edge that may lead to a burnt exhaust valve later on. Inspect the valve guides next. While OEM guides are typically cast iron, manganese bronze guides are a superior, long-wearing alternative. Manganese bronze guides expand with heat at a different rate than the cylinder head, requiring more clearance. A clearance of .003" is often used, which might seem excessive to machinists unfamiliar with these engines, but improper clearance can result in a seized exhaust valve. Hardened exhaust seat inserts are essential for modern unleaded fuels, which burn hotter. Regrinding original cast iron exhaust seats offers only a short-term solution, as valve seal will be lost relatively quickly. Intake valves generally do not require hardened seats as they are not subjected to the same intense heat. The only reason to install intake valve seats is if the cylinder head has undergone numerous previous valve jobs, causing the intake seats to recede. A better alternative in such cases is to use this opportunity to fit larger intake valves for improved performance.

Valve Seat Cutting and Assembly

The most common method for cutting valve seats is the three-angle seat, which enhances performance and sealing. Most machine shops possess specialised tools capable of cutting all three angles simultaneously. The shop will likely resurface the cylinder head to ensure flatness and provide a good sealing surface for the head gasket. Using uprated valve seals is also a wise investment.

Rocker Assembly

It's a good practice to replace the rocker shaft. Inspect the rocker arm bushings and replace them if necessary. Check the wiper section of the rocker arm where it contacts the valve stem. If excessive wear is present, your machine shop can reface them. However, new rocker arms are often not significantly more expensive than the cost of rebushing and refacing your originals.

Other Engine Components

Beyond the core engine components, several other parts warrant attention.

Harmonic Balancer

If your engine is equipped with a harmonic balancer, it will feature a rubber insulator between its inner and outer rings. This rubber insulator can crack and wear over time. A harmonic balancer can be rebuilt, or you can opt for a new one. In some cases, high-performance harmonic balancers are available, offering improved damping characteristics.

Oil Pump

Whether you choose to replace your current oil pump with a new one or reuse the existing unit, it's imperative to disassemble it and check the internal clearances. Your workshop manual will provide the specific clearance specifications. Always use an assembly lube on all moving parts within the oil pump. Never assume a new oil pump is ready for immediate installation without inspection.

Clearances and Precision Blueprinting

It's a common mistake to assume that components are in good condition simply because they 'look' good. Cylinder bores and crankshaft journals, for instance, must be measured by your machinist to confirm they are within specification. Achieving the ideal rod and main bearing clearance, typically between .0015" and .002" for many engines, is crucial. Too much clearance can lead to a loss of oil pressure, while too little can cause damage to the bearings and crankshaft.

The term 'blueprinted' engines refers to a builder specifying exact component sizes to achieve precise clearances. This level of precision is typically undertaken by more advanced engine builders, but your machinist can measure and machine parts to these exacting standards. Proper clearance is critical in numerous areas, including piston-to-cylinder wall, crankshaft end float, camshaft end float, connecting rod side clearance, and valve lash.

Essential New Parts for a Rebuild

A comprehensive engine rebuild often involves replacing several key components. Here's a typical list:

Bottom End Components:

• Piston set: Usually supplied with rings and pins.
• Crankshaft bearings: For connecting rods and main bearings. Tri-metal bearings are often preferred.
• Thrust bearing: Ensure it's the correct size.
• Crankshaft: Replace the pilot bushing. Consider a Speedi-Sleeve if the seal area is worn.
• Cam bearings: Full-circle type is recommended.
• Rod bolts: Replacement is highly advised.
• Camshaft: Replace if needed or desired; consider a performance upgrade.
• Lifters (tappets): Always replace with a new camshaft. Reused lifters must go back to their original positions.

Cylinder Head Components:

• Intake valves: Consider oversize for improved flow.
• Exhaust valves
• Valve guides
• Valve seals
• Valve springs

Rocker Arm Assembly:

• Rocker shaft
• Rocker arm bushings: Replace if necessary.

Gaskets and Ancillaries:

• Engine gasket sets: Quality sets are essential.
• Timing assembly: Always replace the chain, gears, and tensioner. Upgrade to a double-row chain if available.
• Seals: Double-check that all necessary seals are included.
• Oil pump
• Oil pressure regulator parts: Inexpensive to replace.
• Water pump
• Clutch kit

The Assembly Process: A Detailed Approach

With all components cleaned, prepped, and machined, the assembly stage begins. Your workshop manual will be your primary reference. Ensure you have a good quality manual before starting.

Crankshaft Installation and Bearing Check

Begin by test-fitting the crankshaft and bearings. Install the main bearings into the block with a light coat of 30WT motor oil. Then, install the crankshaft and coat its exposed journals with oil. Next, install the main bearings into the main caps, but do not install the caps yet. This is where you'll use Plastigauge to check bearing clearances. Purchase green Plastigauge with a range of .001"-.003". Cut a small piece and place it on the #1 journal. Coat with oil, install, and torque the #1 main cap to the manual's specifications. Carefully remove the main cap and use the graph provided with the Plastigauge to determine the clearance. An acceptable range is .0015" to .002". Repeat this process for each main cap, working from front to back, being careful not to rotate the crankshaft. Once satisfactory readings are obtained, clean the Plastigauge from each journal and bearing shell, and remove the crankshaft.

Lubrication and Final Crankshaft Installation

Utilise a high-quality assembly lube for any area where parts make contact and friction could occur, with the exception of piston-to-cylinder walls. Install the crankshaft and torque the main caps one at a time, starting with the centre cap. After torquing, rotate the crankshaft by hand; it should move smoothly without binding. Ensure assembly lube is applied to every main cap and the thrust washers. After the crankshaft is installed, check its end float to ensure it is within the specifications outlined in your manual.

Piston and Connecting Rod Installation

You will need a piston ring compressor. Apply 30W motor oil to the cylinder walls and piston skirts. Place the ring compressor around the piston, aligning it with the piston rings to compress them. Start with the #1 piston. Ensure the crankshaft is at Bottom Dead Centre (BDC) for the corresponding journal. Take the connecting rod, with the cap removed and rod bearings installed, and insert it into the bore. Verify that the piston is marked 'front' and installed in the correct orientation. Once the piston reaches the block deck, use a dead blow hammer to tamp the top edges of the ring compressor, ensuring it's square against the bore. Use a wooden or plastic hammer handle to tap the top of the piston down into the bore, keeping the ring compressor firmly against the block deck. The piston should slide in smoothly. If resistance is felt, re-check the ring compressor's alignment. If resistance persists, inspect the bottom of the block to ensure the connecting rod isn't interfering with the crankshaft.

After all pistons are installed, rotate the engine to access the bottom side. Follow the same process for rod bearings as you did for the crankshaft, using Plastigauge on each journal individually. Once Plastigauge is checked and cleaned off, apply assembly lube to the rod bearings and install the rod caps. Lube the rod bolt threads with motor oil or a dedicated assembly lube, and torque the rod bolts to the manual's specifications.

Handy Tip: Use a Sharpie to mark components that have been torqued or had clearances checked. This helps keep track of your progress.

Camshaft, Front Engine Plate, and Cam Thrust Plate Installation

Liberally coat the camshaft journals, lobes, and gears with assembly lube. Exercise extreme caution when installing the camshaft into the block, as most nicks and scratches occur during this stage, especially with blocks featuring cam bearings. Install the cam thrust plate, timing gears, chain, and tensioner according to your workshop manual. Ensure the timing marks on the gears are correctly aligned. If using a performance camshaft, you may need to adjust the cam timing as per the manufacturer's instructions, often achieved using offset camshaft keys or an adjustable camshaft gear.

Degreeing a Camshaft

This process involves precise measurement to ensure the camshaft is timed correctly. You will need a degree wheel, a pointer (a piece of wire bolted to the block can suffice), and a dial indicator with a magnetic base. Install the degree wheel and pointer, then position the magnetic base on the block deck towards the #1 piston. Bring the piston to Top Dead Centre (TDC) by rotating the engine. Once TDC is identified, zero the dial indicator's bezel. Rotate the degree wheel to reflect TDC. Double-check this alignment, as any inaccuracy will render your readings incorrect. Install a lubed lifter and pushrod for the #1 cylinder's intake valve. Set the dial indicator on the top of the pushrod. Rotate the engine to find the point of maximum camshaft lift on the indicator. Zero the indicator at this point. The goal is to find the exact same point before and after maximum lift is achieved (e.g., .005" before and after zero). Rotate the engine counter-clockwise approximately .100" before each reading to eliminate timing chain slack. Record the degree wheel readings at these points. Add the two numbers together and divide by two to determine your cam timing. If the timing is incorrect, you'll know which degree of offset key to order or how to adjust an adjustable gear.

Handy Tip: If using an adjustable cam gear, torque the cam retaining nut to the manual's specifications before making adjustments to the gear bolts.

Camshaft End Float

Check camshaft end float similarly to crankshaft end float. Use a magnetic base and dial indicator on the front of the camshaft or gear. Move the camshaft front to rear and record the movement on the indicator. Refer to your manual for the correct specification, typically .002"-.005". If the gap is too large, shimming the camshaft or removing material from the back of the cam gear will be necessary.

Oil Pump and Exterior Assembly

Install the oil pump, remembering to disassemble, clean, lube, and check clearances according to the manual. Lube all points of contact. Install all exterior block bolts, including threaded plugs, oil pressure regulator, distributor drive and base, water pump, timing cover, crank pulley, motor mount brackets, and seals. Grease the lips of seals to prevent damage during installation. Fit the oil pan and gasket.

Lifter, Pushrod, and Cylinder Head Installation

If your engine has external lifter access, install the lifters. Install the cylinder head, ensuring all stud and bolt threads are oiled. Oiling high-torque bolt threads helps achieve accurate torque readings. Install the head gasket, following the manufacturer's recommendations for coatings (most modern composite gaskets require no sealer, while copper gaskets may need a specific spray). Install the cylinder head and rocker arm assembly. Rotate the engine by hand at the front crank bolt and adjust all valves to the recommended lash for your camshaft.

The Final Touches

Complete the engine assembly by installing the valve cover, rear engine plate, flywheel, and clutch. Finally, mount your meticulously rebuilt engine into your vehicle.

Initial Start-Up and Break-In

Fill the engine with all necessary fluids, ensuring you use engine oil with adequate ZDDP content for longevity. Before cranking, check for oil pressure. Remove the spark plugs and crank the engine until oil pressure is registered on the gauge. This may take some time; be patient and give the starter breaks if needed. Never start an engine without confirming oil pressure.

Once oil pressure is confirmed, start the engine. Have your timing light ready to set the ignition timing. Aim for an idle speed of approximately 2,000 rpm and let the engine run at this speed for 20 minutes to break in the camshaft and lifters. During this break-in period, meticulously check for any leaks. After the initial 20-minute run, perform final tuning. Take the car for a short test drive, varying the RPMs between 2,000 and 4,000, and monitoring for any overheating. After a few heat cycles, it's crucial to re-torque the cylinder head and readjust the valve lash.

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