my f350 came with a 6.9 in it . i purchased it used and went today to get an altenator. the alt in the truck was not the same as a stock 6.9 had in it. it is the same as a 90 f350 with a 7.3 . now i know the guy i got it from had the engine replaced since he had a banks kit on it pushing too much boost and blew it up. now i cant seem to find out if they replaced it with a 7.3 instead or someone just put that alt on it. anyone able to help here?

 

the easiest way to tell the difference is the size of the head bolts, a 6.9 has 7/16 headbolts, the 7.3 has 1/2, can't remember what the head size is though

 

On my 91 (7.3), a 12-point 1/2" socket worked on the head bolts. The heads of the bolts looked like stars. Don't know about the 6.9.

Also, when I replaced the alternator, the new one was somehow backwards from the old one. It worked fine, though. I think it depends on how big (amperage) and the brand you go with.

I believe that you can tell by looking at the heads for some kind of reinforcement or webbing on the 7.3. Maybe Dave S can chime in. Also, look for the serial number on the block. Sorry I don't know where it is...

 

You could check the serial number.....located on the flat area of the upper block on the drivers side(USA) just next to the timing/oil filler cover... should have 6.9 or 7.3 in the number.

Here are some differences.....

Cylinder head difference
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Injection nozzles have been retracted on the 7.3 .060" to facilitate Federal and state emission certs.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 cup 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.