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Piston/connecting rod assemblies - refitting and big-end bearing running clearance check
Engine removal and general engine overhaul procedures / Piston/connecting rod assemblies - refitting and big-end bearing running clearance check


1 Before refitting the piston/connecting rod assemblies, the cylinder bores must be perfectly clean, the top edge of each cylinder must be chamfered, and the crankshaft must be in place.

2 Remove the big-end bearing cap from No 1 cylinder connecting rod (refer to the marks noted or made on removal). Remove the original bearing shells, and wipe the bearing recesses of the connecting rod and cap with a clean, lint-free cloth. They must be kept spotlessly-clean!

Big-end bearing running
clearance check
3 Clean the back of the new upper bearing shell, fit it to the connecting rod, then fit the other shell of the bearing set to the big-end bearing cap. Make sure the tab on each shell fits into the notch in the rod or cap recess (see illustration).

18.3 Tab on each big-end bearing shell must engage with notch in connecting
18.3 Tab on each big-end bearing shell must engage with notch in connecting rod or cap

Caution: Dont hammer the shells into place, and dont nick or gouge the bearing face. Dont lubricate the bearing at this time.

4 Its critically important that all mating surfaces of the bearing components are perfectly clean and oil-free when theyre assembled.

5 Position the piston ring gaps as described in Section 16, lubricate the piston and rings with clean engine oil, and attach a piston ring compressor to the piston. Leave the skirt protruding about a quarter-inch, to guide the piston into the cylinder bore. The rings must be compressed until theyre flush with the piston.

6 Rotate the crankshaft until No 1 crankpin (big-end) journal is at BDC (Bottom Dead Centre), and apply a coat of engine oil to the cylinder walls.

7 Arrange the No 1 piston/connecting rod assembly so that the arrow on the piston crown points to the timing belt end of the engine. The cylinder number (counting from the timing belt end of the engine) is etched into the flat-machined surface of the connecting rod and its cap, and must be visible from the front (exhaust side) of the engine (see illustrations 9.5A and 9.5B).

Gently insert the assembly into the No 1 cylinder bore, and rest the bottom edge of the ring compressor on the engine block.

8 Tap the top edge of the ring compressor to make sure its contacting the block around its entire circumference.

9 Gently tap on the top of the piston with the end of a wooden hammer handle (see illustration), while guiding the connecting rods big-end onto the crankpin. The piston rings may try to pop out of the ring compressor just before entering the cylinder bore, so keep some pressure on the ring compressor. Work slowly, and if any resistance is felt as the piston enters the cylinder, stop immediately. Find out whats binding, and fix it before proceeding. Do not, for any reason, force the piston into the cylinder - you might break a ring and/or the piston.

18.9 The piston can be driven gently into the cylinder bore with the end of a
18.9 The piston can be driven gently into the cylinder bore with the end of a wooden or plastic hammer handle

10 To check the big-end bearing running clearance, cut a piece of the appropriate-size Plastigage slightly shorter than the width of the connecting rod bearing, and lay it in place on the No 1 crankpin (big-end) journal, parallel with the crankshaft centre-line (see illustration 17.6).

11 Clean the connecting rod-to-cap mating surfaces, and refit the big-end bearing cap.

Make sure the etched number on the cap is on the same side as that on the rod (see illustration). Tighten the cap bolts evenly - first use a torque wrench to tighten the bolts to the specified (first stage) torque setting, then use an ordinary socket extension bar and an angle gauge to tighten the bolts further through the specified (second stage) angle. Use a thin-wall socket, to avoid erroneous torque readings that can result if the socket is wedged between the cap and nut. If the socket tends to wedge itself between the nut and the cap, lift up on it slightly until it no longer contacts the cap.

Dont rotate the crankshaft at any time during this operation!

18.11 The connecting rod and big-end bearing cap of each assembly must share
18.11 The connecting rod and big-end bearing cap of each assembly must share the same etched cylinder number, visible from the same (front/exhaust) side of the engine

12 Unscrew the bolts and detach the cap, being very careful not to disturb the Plastigage.

13 Compare the width of the crushed Plastigage to the scale printed on the Plastigage envelope, to obtain the running clearance (see illustration 17.10). Compare it to the Specifications, to make sure the clearance is correct.

14 If the clearance is not as specified, seek the advice of a Ford dealer or similar engine reconditioning specialist - if the crankshaft journals are in good condition (see Section 13), it may be possible simply to renew the shells to achieve the correct clearance. If this is not possible, the crankshaft must be reground by a specialist, who can also supply the necessary undersized shells. First though, make sure that no dirt or oil was trapped between the bearing shells and the connecting rod or cap when the clearance was measured. Also, recheck the crankpin diameter. If the Plastigage was wider at one end than the other, the crankpin journal may be tapered (see Section 13).

15 Carefully scrape all traces of the Plastigage material off the journal and the bearing surface. Be very careful not to scratch the bearing - use your fingernail or the edge of a credit card.

Final piston/connecting rod refitting
16 Make sure the bearing surfaces are perfectly clean, then apply a uniform layer of clean molybdenum disulphide-based grease, engine assembly lubricant, or clean engine oil, to both of them. Youll have to push the piston into the cylinder to expose the bearing surface of the shell in the connecting rod.

17 Slide the connecting rod back into place on the crankpin (big-end) journal, refit the bigend bearing cap, and then tighten the bolts in two stages, as described above.

18 Repeat the entire procedure for the remaining piston/connecting rod assemblies.

19 The important points to remember are: (a) Keep the backs of the bearing shells and the recesses of the connecting rods and caps perfectly clean when assembling them.

(b) Make sure you have the correct piston/rod assembly for each cylinder - use the etched cylinder numbers to identify the front-facing side of both the rod and its cap.

(c) The arrow on the piston crown must face the timing belt end of the engine.

(d) Lubricate the cylinder bores with clean engine oil.

(e) Lubricate the bearing surfaces when refitting the big-end bearing caps after the running clearance has been checked.

20 After all the piston/connecting rod assemblies have been properly installed, rotate the crankshaft a number of times by hand, to check for any obvious binding.


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