See Figures 1, 2, 3 and 4
All of the Ford gasoline engines covered in this guide utilize pressed-in wrist pins, which can only be removed by an arbor press. The piston/connecting rod assemblies should be taken to an engine specialist or qualified machinist for piston removal and installation.
A piston ring expander is necessary for removing the piston rings without damaging them; any other method (screwdriver blades, pliers, etc.) usually results in the rings being bent, scratched or distorted, or the piston itself being damaged. When the rings are removed, clean the ring grooves using an appropriate ring groove cleaning tool, using care not to cut too deeply. Thoroughly clean all carbon and varnish from the piston with solvent.
Inspect the pistons for scuffing, scoring, cracks, pitting, or excessive ring groove wear. If these are evident, the piston must be replaced.
The piston should also be checked in relation to the cylinder diameter. Using a telescoping gauge and micrometer, or a dial gauge, measure the cylinder bore diameter perpendicular (90°) to the piston pin, 2 1 / 2 in. (64mm) below the cylinder block deck (surface where the block mates with the heads). Then, with the micrometer, measure the piston, perpendicular to its wrist pin on the skirt. the difference between the two measurements is the piston clearance. If the clearance is within specifications or slightly below (after the cylinders have been bored or hones), finish honing is all that is necessary. If the clearance is excessive, try to obtain a slightly larger piston to bring clearance to within specifications. If this is not possible, obtain the first oversize piston and hone (or if necessary, bore) the cylinder to size. Generally, if the cylinder bore is tapered 0.005 in. (0.127mm) or more or is out-of-round 0.003 in. (0.076mm) or more, it is advisable to rebore for the smallest possible oversize piston and rings.
After measuring, mark the pistons with a felt tip pen for reference and for assembly.
Cylinder honing and/or boring should be performed by a reputable, professional mechanic with the proper equipment. In some cases, clean-up honing can be done with the cylinder block in the vehicle, but most excessive honing and all cylinder boring must be done with the block stripped and removed from the vehicle.
MEASURING THE OLD PISTONS
See Figures 5 through 9
Check used piston-to-cylinder bore clearance as follows:
- Measure the cylinder bore diameter with a telescope gauge.
- Measure the piston diameter. When measuring the pistons for size or taper, measurements must be made with the piston pin removed.
- Subtract the piston diameter from the cylinder bore diameter to determine piston-to-bore clearance.
- Compare the piston-to-bore clearances obtained with those clearances recommended. Determine if the piston-to-bore clearance is in the acceptable range.
- When measuring taper, the largest reading must be at the bottom of the skirt.
SELECTING NEW PISTONS
- If the used piston is not acceptable, check the service piston size and determine if a new piston can be selected. (Service pistons are available in standard, high limit and standard oversize.
- If the cylinder bore must be reconditioned, measure the new piston diameter, then hone the cylinder bore to obtain the preferred clearance.
- Select a new piston and mark the piston to identify the cylinder for which it was fitted. (On some vehicles, oversize pistons may be found. These pistons will be 0.254mm [0.010 in.] oversize).
See Figures 10, 11 and 12
- When cylinders are being honed, follow the manufacturer's recommendations for the use of the hone.
- Occasionally, during the honing operation, the cylinder bore should be thoroughly cleaned and the selected piston checked for correct fit.
- When finish-honing a cylinder bore, the hone should be moved up and down at a sufficient speed to obtain a very fine uniform surface finish in a cross-hatch pattern of approximately 50-60° included angle. The finish marks should be clean but not sharp, free from embedded particles and torn or folded metal.
- Permanently mark the piston for the cylinder to which it has been fitted and proceed to hone the remaining cylinders.
- Thoroughly clean the bores with hot water and detergent. Scrub well with a stiff bristle brush and rinse thoroughly with hot water. It is extremely essential that a good cleaning operation be performed. If any of the abrasive material is allowed to remain in the cylinder bores, it will rapidly wear the new rings and cylinder bores. The bores should be swabbed several times with light engine oil and a clean cloth and then wiped with a clean dry cloth. CYLINDERS SHOULD NOT BE CLEANED WITH KEROSENE OR GASOLINE! Clean the remainder of the cylinder block to remove the excess material spread during the honing operation.
PISTON RING END-GAP
See Figure 13
Piston ring end-gap should be checked while the rings are removed from the pistons. Incorrect end-gap indicates that the wrong size rings are being used; ring breakage could occur.
Compress the piston rings to be used in a cylinder, one at a time, into that cylinder. Squirt clean oil into the cylinder, so that the rings and the top two in. (51mm) of cylinder wall are coated. Using an inverted piston, press the rings approximately 1 in. (25mm) below the deck of the block. Measure the ring end-gap with the feeler gauge, and compare to the Ring Gap chart in this Section. Carefully pull the ring out of the cylinder and file the ends squarely with a fine file to obtain the proper clearance.
PISTON RING SIDE CLEARANCE CHECK AND INSTALLATION
See Figures 14, 15 and 16
Check the pistons to see that the ring grooves and oil return holes have been properly cleaned. Slide a piston ring into its groove, and check the side clearance with a feeler gauge. Make sure you insert the gauge between the ring and its lower land (lower edge of the groove), because any wear that occurs forms a step at the inner portion of the lower land. If the piston grooves have worn to the extend that relatively high steps exist on the lower land, the piston grooves have worn to the extent that relatively high steps exist on the lower land, the piston should be replaced, because these will interfere with the operation of the new rings and ring clearance will be excessive. Piston rings are not furnished in oversize widths to compensate for ring groove wear.
Install the rings on the piston, lowest ring first, using a piston ring expander. There is a high risk of breaking or distorting the rings, or scratching the piston, if the rings are installed by hand or other means.
Position the rings on the piston as illustrated; spacing of the various piston ring gaps is crucial to proper oil retention and even cylinder wear. When installing new rings, refer to the installation diagram furnished with the new parts.