Below is a comparison of the differences between our beloved IDI's. All this Information came out of the 1987 7.3L diesel engine technician's update, which was used to quickly bring up to speed a 6.9 diesel mechanic at a Ford dealership. Note that some of the torque specs changed for head bolts later when turbochargers were added to the 7.3, and the 6.9 by third parties. These torque specs are generally 10 lbs over base figures. Also note that the comments regarding flywheel mixing are contradictory with Ford part numbers for the 1987 version of the 6.9 which uses a 7.3 flywheel from the factory.
First year for the 6.9 - 1983
Last year for the 6.9 - 1987
By 1988 all production 7.3
6.9 - Max H.P. 175 Torque 318 ft. lb.
7.3 - Max H.P. 185 Torque 338 ft. lb.
6.9 max torque at 1800 RPM
7.3 max torque at 1600 RPM
Both max HP at 3300 RPM.
7.3 external identification variance from 6.9 - New fuel filter/fuel heater/water sparator, larger/taller cylinder head bolt bosses with ribs. Dual mass flywheel on 5spd.
Crankcase differences
Cylinder bore - 6.9 = 4.00"
Cylinder bore - 7.3 = 4.11"
Stroke for both - 4.18"
Top deck thickness - 6.9 = .500"
Top deck thickness - 7.3 = .560"
Oil drain Back holes - 6.9 = 3/8"
Oil drain Back holes - 7.3 = 7/16"
Cylinder head changes
Cylinder head bolts - 6.9 = 7/16"-14 UNC 5.25" long
Cylinder head bolts - 7.3 = 1/2" - 13 UNC 6" long
Cylinder head bolt washer 6.9 = .105" thick
Cylinder head bolt washer 7.3 = .134" thick
Head bolt torque -
6.9 with new bolts = 75ft. lbs.
6.9 with used bolts = 85ft. lbs.
7.3 new or used = 100ft. lbs.
Cylinder head gasket changes -
Fire ring I.D. 6.9 = 4.14"
Fire ring I.D. 7.3 = 4.22"
Gasket cutouts elimitated between cylinders on the 7.3 to eliminate cosmetic corrosion phenomenon.
Viton oil drain back sealing rings added to the 7.3 (also used in later versions of the 6.9 head gasket, then eliminated again).
Head design changes -
6.9 features "centered" glow plugs, while 7.3 are "off-center"
Injection nozzles have been retracted on the 7.3 .060" to facilitate Federal and state emission certs.
Precombustion chamber volume -
6.9 = 18.34 cm3
7.3 = 20.42 cm3 (increased only for emissions certs)
Precombusion chamber inserts are physically interchangable, however the throat has been redesigned to distinguish them apart, and the 7.3 prechamber cub has an embossed "88" on it.
Valve Stem -
The 7.3 valve stem oil sheild is larger to reduce hydrocarbon emissions. Intake and Exhaust sheilds have been color coded, even though they are identical and interchangeable.
Coolant passages -
The lower corner coolant passages on the cylinder head on the 7.3 have been plugged. This change is introduced to eliminate lower corner gasket coolant seepage during cold start engine warm-up. Mating passages in the block are also plugged. (could be why we hear more 7.3 overheating issues).
Exhaust valves - The 7.3 exhaust valve has had its alloy composition changed, with more nickel, chrome, and silver content, and decreased manganese content. The 7.3 valves may be used in the 6.9, but not the other way around.
Piston and ring sizes increased in accordance with bore changes. The 7.3 utilizes select fit pistons at the manufacturer. The engine is produced with A,B,C and D size pistons and cylinder bores. When re-using pistons, "A" pistons should go in "A" cylinders, and "B" pistons in "B" cylinders and so on. These letters are stamped on the pistons and the cylinder bores at the bottom of the bore when viewed from the crankshaft side. Service part pistons can be utilized in any bore, and are identified with an "S".
Flywheel -
IMPORTANT. DO NOT USE 6.9 flywheel or vibration damper on 7.3 or vice versa. If components are intermixed, engine vibration and premature component wear may be encountered. For identification, compare these part numbers.
Vibration damper 6.9 1805414C1
Vibration damper 7.3 1809117C1
Flywheel Auto 6.9 1803219C1
Flywheel Auto 7.3 1809212C1
Flywheel manual 6.9 E7TA-6477-AB
Flywheel manual 7.3 E8TA-6477-AA
Injection Pump - Changes have been made to increase fuel flow and change ignition timing on the 7.3. Low and High altitute calibrations are available for both.
6.9 High - 1807568C91
6.9 Std. - 1807560C91
7.3 High - 1809045C91
7.3 Std. - 1809121C91
Injection lines - Due to the .060" retraction of the injector nozzle on the 7.3, all 7.3 injector lines have been shortened by .060" However, all lines with the exception of #1 on F series, and #4 on E series, are interchangeable between 6.9 and 7.3.
Cylinder wall honing -
Plateau cylinder wall honing has been implimented on the 7.3 to promote ring seating and engine break-in.
Front cover -
The 7.3 features an embossed front cover to improve sealing and eliminate water pump replacement due to gasket seepage.
First year for the 6.9 - 1983
Last year for the 6.9 - 1987
By 1988 all production 7.3
6.9 - Max H.P. 175 Torque 318 ft. lb.
7.3 - Max H.P. 185 Torque 338 ft. lb.
6.9 max torque at 1800 RPM
7.3 max torque at 1600 RPM
Both max HP at 3300 RPM.
7.3 external identification variance from 6.9 - New fuel filter/fuel heater/water sparator, larger/taller cylinder head bolt bosses with ribs. Dual mass flywheel on 5spd.
Crankcase differences
Cylinder bore - 6.9 = 4.00"
Cylinder bore - 7.3 = 4.11"
Stroke for both - 4.18"
Top deck thickness - 6.9 = .500"
Top deck thickness - 7.3 = .560"
Oil drain Back holes - 6.9 = 3/8"
Oil drain Back holes - 7.3 = 7/16"
Cylinder head changes
Cylinder head bolts - 6.9 = 7/16"-14 UNC 5.25" long
Cylinder head bolts - 7.3 = 1/2" - 13 UNC 6" long
Cylinder head bolt washer 6.9 = .105" thick
Cylinder head bolt washer 7.3 = .134" thick
Head bolt torque -
6.9 with new bolts = 75ft. lbs.
6.9 with used bolts = 85ft. lbs.
7.3 new or used = 100ft. lbs.
Cylinder head gasket changes -
Fire ring I.D. 6.9 = 4.14"
Fire ring I.D. 7.3 = 4.22"
Gasket cutouts elimitated between cylinders on the 7.3 to eliminate cosmetic corrosion phenomenon.
Viton oil drain back sealing rings added to the 7.3 (also used in later versions of the 6.9 head gasket, then eliminated again).
Head design changes -
6.9 features "centered" glow plugs, while 7.3 are "off-center"
Injection nozzles have been retracted on the 7.3 .060" to facilitate Federal and state emission certs.
Precombustion chamber volume -
6.9 = 18.34 cm3
7.3 = 20.42 cm3 (increased only for emissions certs)
Precombusion chamber inserts are physically interchangable, however the throat has been redesigned to distinguish them apart, and the 7.3 prechamber cub has an embossed "88" on it.
Valve Stem -
The 7.3 valve stem oil sheild is larger to reduce hydrocarbon emissions. Intake and Exhaust sheilds have been color coded, even though they are identical and interchangeable.
Coolant passages -
The lower corner coolant passages on the cylinder head on the 7.3 have been plugged. This change is introduced to eliminate lower corner gasket coolant seepage during cold start engine warm-up. Mating passages in the block are also plugged. (could be why we hear more 7.3 overheating issues).
Exhaust valves - The 7.3 exhaust valve has had its alloy composition changed, with more nickel, chrome, and silver content, and decreased manganese content. The 7.3 valves may be used in the 6.9, but not the other way around.
Piston and ring sizes increased in accordance with bore changes. The 7.3 utilizes select fit pistons at the manufacturer. The engine is produced with A,B,C and D size pistons and cylinder bores. When re-using pistons, "A" pistons should go in "A" cylinders, and "B" pistons in "B" cylinders and so on. These letters are stamped on the pistons and the cylinder bores at the bottom of the bore when viewed from the crankshaft side. Service part pistons can be utilized in any bore, and are identified with an "S".
Flywheel -
IMPORTANT. DO NOT USE 6.9 flywheel or vibration damper on 7.3 or vice versa. If components are intermixed, engine vibration and premature component wear may be encountered. For identification, compare these part numbers.
Vibration damper 6.9 1805414C1
Vibration damper 7.3 1809117C1
Flywheel Auto 6.9 1803219C1
Flywheel Auto 7.3 1809212C1
Flywheel manual 6.9 E7TA-6477-AB
Flywheel manual 7.3 E8TA-6477-AA
Injection Pump - Changes have been made to increase fuel flow and change ignition timing on the 7.3. Low and High altitute calibrations are available for both.
6.9 High - 1807568C91
6.9 Std. - 1807560C91
7.3 High - 1809045C91
7.3 Std. - 1809121C91
Injection lines - Due to the .060" retraction of the injector nozzle on the 7.3, all 7.3 injector lines have been shortened by .060" However, all lines with the exception of #1 on F series, and #4 on E series, are interchangeable between 6.9 and 7.3.
Cylinder wall honing -
Plateau cylinder wall honing has been implimented on the 7.3 to promote ring seating and engine break-in.
Front cover -
The 7.3 features an embossed front cover to improve sealing and eliminate water pump replacement due to gasket seepage.
