EMD 645 vs 710 — Key Differences for Overhaul Planning
The EMD 645 (introduced 1965) and EMD 710 (introduced 1984) share a common design philosophy but differ in bore and stroke. The 710 has a larger bore (230.2 mm vs 222.3 mm) and produces more power per cylinder. Many 645 engines have been converted to 710 specification ("645E3 to 710" upgrades), so always confirm the actual engine configuration from the locomotive data plate before ordering parts.
1. Crankshaft Inspection
- Main and rod journal diameter: Measure at four points (0°, 90°, 180°, 270°) per journal. Maximum taper: 0.013 mm; maximum out-of-round: 0.013 mm. Grind and undersize if exceeded.
- Crankshaft straightness: Check runout at centre main bearing journal. Maximum: 0.05 mm TIR.
- Surface finish: Journal surface finish should be Ra 0.4–0.8 µm. Rough or scored journals must be polished or ground.
- Magnetic particle inspection (MPI): Required at every major overhaul to detect subsurface cracks at oil holes and fillet radii.
- Undersize availability: Standard undersizes for EMD 645/710 crankshaft journals are -0.25 mm, -0.50 mm, and -0.75 mm.
2. Camshaft Inspection
- Lobe wear: Measure each cam lobe at the point of maximum lift. Replace camshaft if lobe lift is more than 0.5 mm below specification.
- Journal diameter: Compare to OEM specification; maximum wear limit is typically 0.10 mm undersize before replacement.
- Camshaft gear backlash: Check idler gear backlash per OEM spec (typically 0.10–0.20 mm). Excessive backlash causes timing noise and accelerated gear wear.
- Cam follower roller inspection: Replace any rollers showing flat spots, pitting, or seizure marks on the roller pin.
3. Connecting Rod Inspection
- Visual inspection: Inspect for cracks at the rod-to-cap junction, around bolt holes, and at the small-end eye.
- NDT requirement: Magnetic particle or dye-penetrant inspection is mandatory at every major overhaul. Any crack indication is cause for rejection — connecting rods are never repaired, only replaced.
- Bore measurement: Measure big-end bore (with bearing shells removed) for out-of-round. Replace rod if bore distortion exceeds 0.025 mm.
- Small-end bushing: Replace bronze bushing at every overhaul. Measure pin clearance after installation: typically 0.025–0.050 mm.
- Rod bolt condition: Replace connecting rod bolts at every overhaul — they are a single-use torque-to-yield fastener in most EMD specifications.
4. Piston and Piston Ring Inspection
- Piston ring replacement interval: EMD recommends replacing all piston rings (compression, intermediate, and oil control) at every top-end overhaul, regardless of apparent condition.
- Ring end gap: Measure in the cylinder bore. Typical specification: 0.40–0.65 mm for compression rings. Rings with end gap > 1.5 mm should be replaced.
- Piston crown inspection: Inspect for erosion, cracks, or deposits around the bowl rim and valve pockets. Minor deposits can be cleaned; cracks or significant erosion require piston replacement.
- Piston pin (wrist pin): Inspect for wear marks, corrosion pitting, or heat discolouration. Replace if worn beyond OEM diameter tolerance (typically ±0.013 mm).
5. Cylinder Liner Measurement
- Bore measurement positions: Measure at top ring reversal (TRR), mid-stroke, and bottom — at 0° and 90° to crankshaft centreline. Record all measurements.
- Wear limit — 645: Discard bore diameter 222.63 mm (nominal 222.25 mm; maximum wear 0.38 mm).
- Wear limit — 710: Discard bore diameter 230.63 mm (nominal 230.20 mm; maximum wear 0.43 mm).
- Taper and out-of-round: Maximum 0.10 mm taper (TRR to bottom); maximum 0.08 mm out-of-round at any measuring plane.
- Liner honing: Liners within wear limits can be honed to restore cross-hatch pattern before ring installation. Honing angle: 30–45° included angle.
6. Cylinder Head Inspection
- Pressure-test heads to 550 kPa (80 psi) with water; hold 10 minutes. Reject any head showing seepage.
- Inspect valve seats for recession; grind or replace inserts as required.
- Replace all cylinder head gaskets and O-rings at every overhaul.
- Check injector bore for wear or carbon buildup; clean and inspect injector hold-down threads.
Overhaul Category Summary
| Component | Top-End Overhaul | Major (Complete) Overhaul |
|---|---|---|
| Piston rings | Replace | Replace |
| Cylinder liners | Measure / hone | Replace if at limit |
| Connecting rod bolts | Inspect | Replace |
| Crankshaft bearings | Inspect | Replace |
| Crankshaft NDT | Not required | Required |
| Camshaft | Inspect | Replace if worn |
| Cylinder heads | Pressure test | Pressure test + valve reconditioning |
Parts from Supco Canada
Supco Canada stocks overhaul kits and individual components for EMD 645 and 710 engines including piston ring sets, cylinder liner sets, bearing sets, gasket kits, and cam follower assemblies. All parts are available with full material certificates and ISO 9001:2015 certification for export to international railway customers.