, Simor engineering · EMD
EMD 645 vs 710: what interchanges and what does not
The 710 grew out of the 645, so buyers assume the parts carry over. Assembly by assembly: what does, what never does, and how to read the variant before ordering.
The EMD 710 entered service in 1984 as a development of the 645, which had been in production since 1965. Both are two stroke, uniflow scavenged, 45 degree vee engines with four exhaust valves per cylinder and a 9 1/16 inch bore. The 710 lengthened the stroke from 10 to 11 inches, which is where the two names come from: 645 and 710 cubic inches per cylinder. That single change reached into the crankcase, the power assembly and the timing, and it is why the two series share less than the family resemblance suggests.
This note is written for the person placing the order. It lists the assemblies that never cross over, the ones that sometimes do, and the three things to read off the engine before a part number goes on a purchase order.
10 in / 11 in
stroke, 645 versus 710
9 1/16 in
bore, shared by both series
1965 / 1984
first production year
8 to 20
cylinders across the two families
Why the confusion happens
Three habits cause most wrong orders. First, parts books for the two series use similar numbering and many accessories genuinely share numbers, so a buyer who has seen one match assumes the next. Second, fleets are mixed: a workshop that runs 645 powered units alongside 710 powered units keeps one spares list and one bin. Third, the engine on the nameplate is not always the engine in the frame after forty years of overhauls and re-powering.
Assemblies that never interchange
| Assembly | Why it is series specific | What to check |
|---|---|---|
| Power assembly (liner, piston, carrier, rod, head) | Stroke and compression height differ; liner and head seat to a taller 710 crankcase. | Order by series and rating; a 645 head does not seat on a 710 liner despite the similar bolt pattern. |
| Crankshaft and main bearings | Different throw, different counterweighting. | Serial and series on the nameplate; overhaul records for a replacement crank. |
| Camshafts, cam bearings and timing gear | Timing changed with the longer stroke. | Never mix segments between series. |
| Fuel injection | 645: mechanical unit injectors. 710: mechanical on early G3, electronic (EMDEC) on ECO and later. A matched set. | Confirm mechanical or electronic from the nameplate rating and the presence of an ECM. |
| Turbocharger and mounting | Turbo models and adaptors are matched to series and rating; a roots blown 645E has no turbocharger. | Read the turbo nameplate as well as the engine nameplate. |
| Crankcase and oil pan | Different height and bore spacing tolerances. | Not a spare part in practice; relevant for re-powering. |
Assemblies that often interchange, with conditions
- Cooling and lubrication: water pumps, oil pumps, coolers and their piping frequently share numbers across adjacent ratings. Check the parts book for the specific rating, not the series.
- Governors and protection devices: the Woodward governor and overspeed trip families overlap; the setting and the drive differ by rating.
- Gaskets, seals and hardware: interchangeable where the parts book shows one number; a visually identical gasket with a different number is different for a reason.
- Electrical accessories: many sensors, switches and harness components are common, but not on electronic injection variants.
- Air box and exhaust manifold components: sometimes shared within a rating band; verify by number.
Read the variant before you order
Four things to send with every order
-
1
Nameplate
Model (for example 16-645E3B or 16-710G3B), serial and rated speed. The suffix carries the aspiration and the rating; E is roots blown, E3 is turbocharged, G3 variants are 710 ratings.
-
2
Locomotive class and re-powering history
A frame built for a 645 can be running a 710 today. The last overhaul report tells you what is in the frame now.
-
3
Injection type
Look for an engine control module and electronic injectors. If present, the engine is on the electronic side of the family and the injection parts are a different list.
-
4
Parts book edition
Quote the edition or the date. Numbers were superseded over the decades, and a superseded number is where most probable matches come from.
Tender the engine model and rating on every line, not only the part number. Allow qualified alternatives for consumables and make the supplier state the series on the quotation.
Keep two bins and two lists. Where a number is shared across series, label it shared; where it is not, label the series. Most cross contamination happens at the bin, not at the order.
Marine and stationary 645 and 710 variants differ again in cooling, exhaust and governing. Give the application with the model; a locomotive parts book is the wrong reference.
Worked example
A request arrives for 16 cylinder heads against a fleet listed as 16-645E3. The nameplate photograph shows 16-710G3A on four of the units, re-powered ten years earlier. Without the photograph the quotation would have carried the wrong heads for a quarter of the fleet. With it, the quotation carries two lines, each with the series stated, and the buyer's tender file shows why.
Questions we are asked
- Can a 645 be upgraded to 710 parts?
Not by parts substitution. Re-powering replaces the engine. Some 645 assemblies were themselves upgraded over the years (for example later liner and piston designs), which is a different question and one the parts book edition answers.
- Are 567 parts relevant here?
The 567 preceded the 645. Some 567 engines were converted to 645 power assemblies with specific kits; treat 567 as its own list and confirm conversion status from records.
- How do you handle a superseded number?
We quote the current number, state the superseded one it replaces, and record the reason. Your file shows both.
Send the nameplate and the list; interchangeability is checked before the quotation, not after delivery.
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