Hummer H3. Manual — part 397

19. Measure the piston diameter for size with a micrometer or caliper at a right angle to the pin

center line, across the skirts, 38 mm (1.50 in) from the top of the piston.

intermixed without affecting engine balance. If necessary,
used pistons may be fitted selectively to any cylinder of the
engine, providing the pistons are in good condition and the
same weight. Do not cut oversize pistons down or the engine
balance may be affected. Finish hone when selecting the
piston.

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

Fig. 426: Measuring Cylinder Bores With J 8087
Courtesy of GENERAL MOTORS CORP.

20. Replace the piston if worn beyond specifications or if damaged.

21. Use J 8087 to measure the cylinder bore. See Special Tools.

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

Fig. 427: Honing Cylinder Bore
Courtesy of GENERAL MOTORS CORP.

22. Hone to size if necessary. Use the following procedure to hone the cylinder bore to the

correct size.

1. Select a piston.

2. Hone the cylinder bore to obtain the recommended clearance.

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3

3. Clean the piston and cylinder bore with soap and water. Dry the cylinder bore and

piston. Lubricate the cylinder bore with clean engine oil.

23. Use the following procedure to measure the piston-to-cylinder bore clearance.

1. Subtract the piston diameter from the cylinder bore diameter to determine the piston-

to-bore clearance.

2. Compare the piston-to-bore clearance using the specifications to determine if the

clearance is in the acceptable range.

3. If the used piston is not acceptable, a new service piston may be selected.

24. When a piston has been selected, mark the piston to identify the cylinder for which the

piston was fitted.

25. Select a set of new piston rings.

26. Install each ring, one at a time, into the corresponding cylinder.

27. Install the piston for that cylinder, upside down (top of piston pushing on the ring) and push

the ring to approximately 25 mm (1 in) down from the deck surface.

28. Remove the piston.

29. Measure the ring end gap with a feeler gage.

2007 Hummer H3

2007 ENGINE Engine Mechanical - 3.7L - H3