Mercury XR3Z-6108-JA Piston And Pin Assembly

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Before installing piston/connecting rod assemblies, ensure clean cylinder walls, chamfered top edge of each cylinder, and crankshaft in place. Remove cap from end of number one connecting rod, wipe original bearing inserts' surfaces. Place upper and lower bearing inserts in connecting rod and cap, align tabs. Position piston ring gaps, lubricate piston and rings with oil. Use ring compressor to insert assembly into number one cylinder bore, tap piston into place, guide connecting rod onto crankshaft journal. Check connecting rod bearing oil clearance with Plastigage before bolting rod cap. Tighten nuts to specified torque, check Plastigage for oil clearance, scrape off traces if correct. Apply moly-base grease or assembly lube to bearing faces, slide connecting rod back into place. Repeat procedure for remaining pistons/connecting rods. Rotate crankshaft to check for binding, verify connecting rod endplay, resize rods if necessary at machine shop.

You should check for ridges at the upper limit of ring travel using your fingernail.

Employ a piston ring groove cleaning tool or a section of a broken ring to clear carbon deposits from the ring grooves without damaging the metal.

Check the piston-to-bore clearance by measuring the bore and the piston diameter. Measure the piston across the skirt, at a 90-degree angle to, and in line with, the piston pin. Subtract the piston diameter from the bore diameter to obtain the clearance. If it's greater than specified, the block will have to be rebored and new pistons and rings installed.

After the cylinder ridges have been removed, turn the engine upside-down so the crankshaft is facing up.

If the clearance is not correct, check for dirt or oil between the bearing inserts and the connecting rod or cap, and recheck the journal diameter. If the Plastigage was wider at one end, the journal may be tapered.

Clean the back side of the other bearing insert, install it in the rod cap, ensure the tab on the bearing fits into the recess in the cap, and do not apply any lubricant. The mating surfaces of the bearing and connecting rod must be perfectly clean and oil-free when assembled.

Before the connecting rods are removed, check the endplay with a dial indicator or with feeler gauges. Slide them between the first connecting rod and the crankshaft throw until the play is removed. The endplay is equal to the thickness of the feeler gauge(s).

If the pistons and cylinder walls aren't damaged or worn excessively, and if the engine block is not rebored, new pistons won't be necessary. Normal piston wear appears as even vertical wear on the piston thrust surfaces and slight looseness of the top ring in its groove. New piston rings should always be used when an engine is rebuilt.