Engine and Gearbox

The Engine and gearbox or enjin en ratkas as they are sometimes called in South Africa, are usually good runners when the Engine and Gearbox are salvaged from an accident damaged car, ldv, truck or bakkie, in fact any wreck, provided that the head, block and sump, gearbox casings etc are not too severely damaged in the collision. You can usually see how the vehicle was impacted and make a reasonable assessment of the extent of the accident damage. When the transmission is damaged, and this often occurs with convertible or cabriolet cars when hit hard, as if ‘wrapped around a tree type of accident’, then caution is to be exercised when buying these wrecked car components.

Sometimes the propeller shaft is hit square from behind, moves forward and breaks internal parts within the gearbox, including the casings that are made from magnesium and cannot be welded back together. Again the internal parts are what you are probably after. A reputable gearbox shop that specializes in either automatic transmissions or manual gearboxes is what you are after to rebuild your existing gearbox that has malfunctioned. To source a gear box casing or bell housing, which are a plenty in their back yards and in most cases it would be a better bet to buy a gearbox on exchange.

In my years as an engine builder I have never found a qualified mechanic that could build up a gearbox on request, but just about every single so called mechanic can pull an engine, strip it and put it back together. I have even seen them pull engines out on the side of the road and when I come back that way a few days later I see them refitting the engine after a ‘roadside engine rebuild’. I can’t say I have ever seen anyone strip a gearbox like that, a clutch job yes, but this is Africa!

Cabriolets and Convertibles

Cabriolet and convertible cars don’t have much structural strength at all because the roof strength is absent and these cars collapse a lot easier as they have only to the floor chassis to rely on for stiffness and strength. Modern cars with solid roofs have the windscreens glued in with a powerful polyurethane adhesive and bonding agent, bonding the glass to the vehicle. The combined strength of a laminated windscreen and the roof of a car or truck ad’s immense strength to the vehicle compared to a cabriolet or convertible without a roof. Windscreens on most vehicles are curved (convex on the outer), making a windscreen almost impenetrable from the outside, although weak on the inside. The laminating resin used to bond the two layers of glass together is unbelievably strong. We found it almost impossible to tear a length just 100 mm x 300 mm in half in its bare state with our hands

Crash Test Technology

Through the years crash test technology has indicated that it is far better to keep the occupants of vehicle inside the car when involved in a collision. Old model cars simply had the windscreens pushed into a rubber molding or beading. These windscreens became flying objects when vehicles were involved in head-on collisions and if the vehicle rolled over, the windscreen would simply fall out or collapse into the vehicle, injuring the driver further. Vehicle manufacturers came to realize that bonding the windscreen to the vehicle was the best way to go. This process has proved to save countless lives and reduced injuries drastically over the years since it was first introduced back in the 80’s. Some cars like the Golf 1 still carried on producing rubber moldings until recently.

If the car has not been stripped yet, ask the scrap yard manager to get his vehicle dismantlers to strip out the engine. Do this only once he has told you that the engine and gearbox is still in the vehicle. You want to see the engine and gearbox in the vehicle. Most scrap yards offer a 30-day ‘running guarantee’ on all suitable salvaged parts. To buy a vehicle in that state would definitely be risky and left alone for the experts. You can’t afford to have a come back or take back. It’s easy for the scrap yard dealer to say to you ‘just bring it back’. Try fitting a gearbox, then having to take it out again because of some unforeseen technicality.

The Engine Cylinder Block

During much of the pre-1930 era it was common to build up the engine using a two-piece cylinder block. The part housing the cylinders was cast iron, either in unit with or separates from, the cylinder head. The lower part housing the crankcase was an aliminium casting, and so was the sump. For many years cast iron has been used for engine blocks, but at present it is considered too heavy for petrol units, but is still the material of choice for most diesel engine blocks.

Modern petrol engine cylinder blocks are cast using aliminium because the reduction in mass is desirable. The recent BMW straight-six engine gained a two-piece magnesium/aluminium cylinder block to reduce mass on the front wheels by nearly 14kg. This helps to promote a near 50:50
weight distribution.

Until the early 1920’s most engines were fitted with cast iron pistons, but these were later replaced by aluminium pistons. The latter offer a reduction in reciprocating mass as well as superior heat conducting properties. Most production pistons are cast from alloys having a high silicon content, but racing pistons are usually forged. Forging is a superior but also a more costly process, and a stronger alloy can be used.

The cylinder bores are either loose cast iron sleeves or the bare aluminium treated with a coating or chrome spots are introduced using a special process. Failing to do this would result in excessive wear, as aluminium is not wear-resistant.

Cast iron and is extremely hard and tough, but very brittle, and usually survives the regular collisions without breaking anything that cannot be welded or machined back together, should you need to. The block is protected to a certain degree by the rubber engine and gearbox mountings including the prop shaft centre mounting which is rubber mounted, so these components can absorb a tremendous amount of shock at the impact zone, allowing a certain amount of flexibility.

These rubber mounts usually break off on impact, saving the engine block from certain breakage. The gearbox however sustains more damage mainly to the soft magnesium casings and bell housing. If you are looking for a bare block for a late model car or truck the chances are you’ll land up buying a working sub assembly i.e. (the block and sump without the cylinder heads) or a head, block and sump assembly from whoever can supply you with either or. I find that the older model bare blocks are easier to come by than the later ones.

Preparing the Block

If you are starting a long-term project and want the best out of an engine, start with a bare cylinder block. The block is the foundation of any project. Every other component in the engine ultimately depends on it. More time and effort and expense are devoted to preparing the block than any other component. Deburr all the irregularities from when the block was cast and soak it overnight in a caustic soda tank. Remove it and wash it off with Prepsol degreaser.

Align boring is always a good job well done, especially when the block has weathered, meaning that the metal has been stressed to a point of no return and taken to that stressed shape. Torque all your main bearing caps to the usual settings and send it away for ‘align boring’ and honing. Align boring and honing guarantees a perfect line-up through all the main bearing caps and ensures that there is no drag on any of the bearing shells. Not any engineering shop can do this process. So you would have to find out where it can be done closest to you.

The next process is to bore the block to suit your pistons and chamfer the bore entry to 60 degrees. Hone the bores with a 280-320 grit hone.Align the holes between the bearings and the saddles and elongate the bearing shells as necessary.

Crankshafts and Reconditioning

The crankshaft is the most highly stressed component in an engine. Every ounce of torque travels through the crankshaft while the pistons do their best to alternately push the crank out through the bottom of the sump and then pull it toward the cylinder head.

During the sixties, you could be almost certain that any high performance engine had a forged steel crankshaft. The strength of the finished parts depends to some extent on whether the parts have been cast, forged, or machined from a steel solid, and the various alloys are tailored to have the qualities needed for the relevant manufacturing process. The casting process involves pouring liquid metal into a mould, allowing it to set, but forging utilizes two or more dies that force red-hot solid material into the shape required.

Until the early 1930’s most cranks were forged from high strength steel, but Ford started the fashion for casting cranks from a special mix of cast steel alloy. This saved time and money, and the process is used extensively these days. High performance crankshafts are either forged from special alloys if a large quantity is needed, or machined from billet if only a few are required.

High strength steel is used for most connecting rods, although a special aluminium alloy was tried in the past but doesn’t appear to have been very successful. Modern high performance engines tend to use titanium alloy because of its superior strengths.
If your aim is to buy the whole engine for example and strip it ideally for the crankshaft, rods and other internal working parts, ensure that the crankshaft has not sustained unserviceable damage to the nose. Pay particular attention to vehicles that have had serious front-end collisions. This damage will often lead to the crankshaft nose being scarred in some way or other, i.e. the front part where the crank pulley or crank gear slides on and over, often referred to as the nose. Most crankshafts are cast from cast iron alloy, much the same as a engine block and don’t damage that easily when involved in collisions.

Should you be purchasing the complete engine for an expensive hard to come by crankshaft, connecting rods and pistons and the nose is damaged, then it can usually be repaired by having it welded, whether it be a cast iron crankshaft or a steel crank. The crankshaft should be cleaned and dusted with magnaflux for crack detection and inspection before any further work is carried out.

Crank Welding & Stroking

Specialized crankshaft welding companies such as Metweld or Cargo Crankshaft Rebuilding can repair almost any crankshaft by specialized machine welding techniques and a well established engineering firm such as Blue Print Engineering can then index the crank and machine the new woodruff keyway slot for the crankshaft gear, if the crankshaft nose was welded. The crank and rods can now be deburred or shotpeened for any irregular lumps or high spots. This reduces a starting place for potential cracks.

The Crankshafts big end journals can also be welded thicker and ground down to offset the original centre by a few millimeters. Offset grinding the rod journals is an effective way to change the stroke length of a crank. The stroke can be increased or decreased by grinding down the rod journal while simultaneously moving the centre line of the rod throw. This process is referred to as ‘stroking the crankshaft’’. What the process is actually doing, is making the crankshaft push the pistons a little further up and down, increasing the diameter of rotation on it’s main axis, (the main bearing journals). This increases the ‘stroke’ of a motor, and increased stroke gives an engine low end torque. These engines don’t rev as fast as the shorter stroke motors but give great punch. I only recommend stroking steel cranks, as the cast iron does not finish up as nicely even once the crank journals have been micropolished. Some crankshaft engineers improve the hardness of the journals by hard chroming them, coating only the journals.

Connecting Rods

Life is never easy for a connecting rod. With every turn of the crankshaft, it is alternatively stretched and compressed. The motion of the crank tries to snap the conrod beam in half, while the big end and small ends are baked with intense heat. Considering the environment they live in the survival rate among connecting rods is remarkably high.

Polishing the conrod is cheap insurance for any conrod. It’s a task you can easily do at home. Start by deburring the uneven or raised casting marks or forged marks along the sides of the conrods with an air die grinder and an engineers file. This will help prevent stress cracks from developing, denying them a starting place. High strength aftermarket conrod bolts can be installed for any engine. Rod bolts are designed to stretch. It is this carefully controlled spring action that keeps the nut tight and provides the clamping force.

When the big end of a conrod distorts, the bearing and crank journal is in for trouble. The constant rapid changes in direction can cause the big end to become egg-shaped. Like align boring and honing a cylinder blocks main journal caps, resizing stock conrods is an essential part of engine blueprinting. (Apply this process particularly to weathered engines).

Pistons

Aluminium pistons are rather amazing. They are alternately burnt by the heat of combustion and then blasted by a cold jet of air with every intake stroke. They are accelerated and decelerated at a tremendous speed at every turn of the crankshaft, while withstanding side loads that try to weld the piston skirts to the cylinder walls of the sleeves. The harder the driver of the vehicle puts his foot on the gas the harder the environment for these components become, and must endure one thing: increased cylinder pressure. The higher the pressure in the cylinders, the higher the loads the pistons must endure.

Cylinder Heads

An engine’s cylinder head ports are the pathways to power! The air and fuel mixture that passes through them are the sole source of energy. No matter what standard you apply to engine performance – horsepower, torque, fuel economy or response – it’s the valves, seats, and ports that are finally responsible for how well the motor performs.

The valve seats are where the valves meet the cylinder heads. The seats are the most critical area in the engine in terms of airflow. Every molecule of fuel and oxygen mixture the engine burns must pass through these critical points.

Since air is invisible, it is sometimes difficult to imagine how it moves through an engine. It may help to visualize air as if it were a liquid. Picture a wild river brimming with rocks and boulders; you will have a good idea of the obstacles in the pathway of the air/fuel mixture as it winds through the head ports. As the water in this imaginary river rushes downstream, it forms turbulent whirlpools as well as stagnant pools where there is little movement. These white water rapids make river travel difficult. A smooth flowing river channel seems tame in comparison, but it does a better job of moving large volumes of water.

Like the water in the river, air/fuel mixture that flows through an engine has mass. Obstacles in the path and quick changes in direction cause it to become turbulent; it forms invisible swirls and whirlpools. As a result, fuel droplets, which are heavier than the air molecules that surround them, separate from the main flow and collect in pockets, like driftwood along the banks of a river. Since this upsets the delicate balance of fuel/air mix that is needed for optimum power, engine performance suffers. So the goal of most cylinder head work is to create the conditions that allow the ‘river’ of fuel and air to move through the ports as smoothly as possible.

Valve seats in factory-installed heads are designed for durability, not maximum airflow. Factory valve seats are ground at only one angle-usually a 45-degree cut, although some automakers use a 30 or 37-degree seat angle cut into the seats. Modern machinery allows for multiple seat angles to be cut into seats allowing a less abrupt flow of gasses to enter and exit the ports, causing fuel droplets to fall out of the air stream and collect on the port walls and valve heads, which causes the air/fuel mixture to suffocate. Usually the seat gets a 3-angle cut.

Camshafts

The camshaft has often described as the ‘brain’ of the engine. In effect the camshaft regulates engine ‘breathing’ by opening and closing the valves. Cam profiles regulate and compromise at low engine speeds and during part-throttle operation, an engine needs a camshaft design with a short duration and relatively little valve lift to produce sharp throttle response and good fuel economy. At high rpm, however, there is very little time to fill the cylinders, so a long-duration cam with high valve lift is the answer. There are a staggering variety of cam designs available for modern performance engines. Most modern cars have variable valve cam timing computers that advance and retard the cam continuously while driving to attain the maximum torque and power.