SHORT BLOCK COMPONENTS Chapter 2 Short block components PISTONS AND CONNECTING RODS The choice of parts depends on the application. The majority of modified engines (1600, 1800 and 2000) are built using standard parts such as oversized standard cast pistons and connecting rods in freshly rebored cylinders. There is little point in using a block which has more than 0.05mm/ 0.002in bore wear: in fact, there s very little point in modifying an engine that has any bore wear at all. There is no substitute for a perfectly parallel cylinder bore. AE cast aluminium over size pistons are available for all Pinto engines in plus 0.020inch/0.5mm, 0.030inch/0.75mm, 0.040inch/1.0mm and 0.060inch/1.5mm over sizes. The standard cast aluminium pistons for all Pinto engines are rated as being suitable for use up to about 7000rpm; which means that the standard pistons are slightly stronger (in rpm terms) than the standard connecting rods. An engine used on the race track equipped with standard type cast pistons and standard con- necting rods and being revved consistently to 7000rpm will most likely end up having a connecting rod failure rather than a piston failure. In most instances it is the 2000cc version of the Pinto engine that gets modified because it is the largest capacity engine. Most of the alternative equipment is made to suit these engines so the following information refers mainly to them. Standard 2000cc Pinto piston and pin. A standard type cast piston is available from AE in plus 0.090inch/ 2.25mm for 2000cc engines which takes the capacity out to 2.1 litres. There is no weight difference over the standard piston. These pistons are drop in fit items once the block has been bored out, and are compatible with the standard type connecting rods. Note that engines (with compo- 15
Main bearing tunnel bore surface as machined by the FoMoCo. Nothing less than this finish will do. Cap being tapped down into the register of the block. the main caps, main cap webs, the block s deck surface and the area around all tapped holes. Cracks are frequently quite easy to see. Engines that have only ever been used in roadgoing vehicles seldom have cracked blocks. If there is an obvious major crack, the block is a write-off and further checking is pointless. Main bearing caps The main caps fit into the block rather than onto the block. This fit is by way of a machined register in the block in which the cap is a tight fit. If, instead of needing to be tapped in, a cap simply falls into its register, the block is not suitable for further use. With the register and the base of the main cap scrupulously clean, the main cap is positioned onto the block (with the arrow pointing to the front of the block) with one edge of the cap located in the register while the other edge of the cap is up on the other register. The cap is held with a definite bias toward the left and the top righthand side of the cap tapped downwards so that the cap snaps into the block s register. Two or three very light taps with a small copper hammer or Location tabs on main bearing shells (inserts). rawhide hammer is all that it will take. With the cap correctly located the two main cap bolts are oiled, then screwed in and torqued to the correct tension. Note: it is assumed that the threaded holes in the block were thoroughly Main bearing tunnel bore being measured in the vertical plane and at 70 degrees to the left and right of the vertical plane. 32
SHORT BLOCK REBUILD cleaned out and that the threads of the bolts were thoroughly cleaned, too. With the cap fully torqued, the tunnel aperture is measured with an inside micrometer and the size checked against the manufacturer s specifications. Ford list the main bearing tunnel bore diameter tolerance (range of acceptable size) as 60.620-60.640mm/2.390-2.395in. The tunnels must be within this range. The small measurement is known as bottom size and the larger as top size. The optimum size is bottom size. Reject any main bearing tunnel bore measurement over top size, but note that blocks can be remachined by an engine reconditioner to restore optimum, or acceptable, main bearing tunnel bore sizes. The first of three measurements is taken in the vertical plane and in the middle of the main bearing tunnel. The second measurement is taken 70 degrees left of the vertical plane and the third measurement is taken 70 degrees to the right of the vertical plane. With three measurements taken in these places the integrity of the main bearing tunnel can be clearly ascertained. The surface finish of the main bearing tunnel bores should be very smooth (the same as a freshly honed cylinder bore with a cross hatch pattern). There should be no marks indicating a spun (bearing shells have rotated in their housing) bearing and, if there are, even if the tunnel measures as being in tolerance, the block will have to be align bored or align honed to remedy the situation. Check-fitting main bearing shells With the integrity of the block s bearing tunnels confirmed as being on size (at bottom size or top size or in between) the new bearing shell inserts First step in fitting a bearing shell. The location tab is positioned in the machined groove 3mm/0.25in down from the mating surface. How the bearing shell should be pushed down into the tunnel. Shell correctly positioned in the block with the ends at equal heights. that are going to be used in the engine at final build must be check-fitted to the block. Bearing shells are very The easiest way to remove a shell is to push it with your thumb in the direction arrowed. accurately made, but, as with all mass produced components, there is always some dimensional variation (however small). In the first instance the bearing shell inserts are randomly paired up and fitted to a main bearing housing. Each shell/cap combination is then checked for bearing crush to see just how tightly the bearing shell inserts are actually held in the main bearing tunnel. The bearing shell inserts can be mixed and matched to a certain degree to get an even and acceptable amount of bearing crush. The usual procedure is to start at the rear of the block and work forward. This usually proves to be most convenient, especially if the engine block is being held on an engine stand, as the main bearing furthest away from you is worked on first. Once a pair of bearings shells have been check-fitted they must be labelled as belonging to the particular main bearing tunnel in which they were checked. Clean the new bearing shell thoroughly using thinner and soft paper towels to remove all traces of dirt or protective grease from the backs of the inserts and the bearing surfaces. The bearing tunnel halves are also cleaned (block and cap). 33
Feeler gauges should be positioned as shown to prevent bearing damage when the connecting rod bolts are tightened. and the actual surfaces of the bearing inserts can be damaged. Caution: check that the socket used to tighten the nuts does not contact the connecting rod cap. If the socket does contact the cap it can become misaligned or the nut can give Connecting rod check-fitted to crankshaft to test freedom of rotation. a false torque reading. With the connecting rods fitted, the crankshaft is lifted up so that it is vertical (resting on the rear flange), or the nose is clamped in a vice with protective shields fitted between the vice jaws and the nose. The connecting rods are each then checked for freedom of rotation for the full 360 degrees. By turning the connecting rods one at a time any binding will be felt. If there is binding, remove that particular connecting rod, refit the cap and then re-measure the bearing insert bore diameter in three places and especially across the bore where there are scuff marks. This is to check the overall roundness of the bearing bore. Caution: use a feeler gauge between the connecting rod and crankshaft during all assembling and dismantling to avoid any possibility of damage to the bearing shell inserts. If there is binding there will be some scuffing of the bearing insert surface but it can be very difficult to see at times. Use a magnifying glass if necessary. Bearing inserts can have high spots at times but this is unusual. If there is a high spot it can be eased with a three-corner scraper but never with wet-and-dry abrasive paper. Check to make sure that it is a high spot and that there is not a general overall lack of bearing clearance or debris behind the inserts. Check the bearing bore size of the connecting rod and for misalignment of the cap as this can be caused by the socket becoming jammed against the connecting rod cap. This is a dummy assembly designed to check the actual fit of all of the connecting rods on the crankshaft. All of the sizing was established by direct measurement using micrometers; the fitting of the connecting rods is done to double check working clearances. With this procedure carried out and the bearing clearances proved correct, or found to be incorrect and the situation remedied, the connecting rod to crankshaft check fitting is complete. BUILDING THE SHORT BLOCK Freeze plugs have been known to come out of cylinder blocks and cylinder heads. Any competition engine needs to have some form of retention across all of the freeze plugs so that if one comes lose at least it will not fall out. When the crankshaft is being installed it must be very carefully lowered into the oiled bearings in the block and must not be rotated. The main bearing caps (oiled bearing shells and thrust washers included) are then fitted to the block and snapped in, the bolts fitted and torqued to the correct tension. Only now can the crankshaft be turned because the shell bearings 46
Twin plate AP racing clutch on lightweight aftermarket flywheel. Top - the rear (block side) of a lightened standard Pinto flywheel. Above - the front (clutch side) of the same lightened flywheel. frequently than desirable. Overspeeding the engine even once could be once too often! Don't take this sort of risk as it is just not worth it. All standard Pinto flywheels can be lightened. To make a worthwhile reduction in weight, material only needs to be removed from the back of the flywheel (faces the block). The clutch side of any used flywheel must be cleaned and trued which involves removing 0.25-0.50mm/0.010-0.020in from the clutch plate and pressure plate location surfaces. Pinto flywheels are quite tough to machine, so the removal of the necessary material will take considerable time. Note that the surface on which the clutch plate runs will have to be ground true if it shows signs of having been overheated, as these heat marked surfaces are very hard and not easy to turn using a tungsten carbide tool. It s better to grind the surface because a turned surface, while looking quite good, will usually have high spots right where the overheating took place. Burton Power sell 5 lightweight (9 to 12 pound) steel flywheels for six bolt retention SOHC Pinto engines and 9 bolt retention Cosworth crankshaft equipped engines. They sell AP Racing up-rated pressure plates and clutch driven plates of either organic lining material or cerametallic linings on paddle clutch plates. The AP Racing cerametallic clutch assembies are virtually indestructable no matter how much abuse the clutch is given. They are essential for rigourous racing 94