i have just bought a 1986 ford f350 with a 6.9 diesel, its a beast and i love driving it. i plan on putting the 6.9 diesel in my 79 f250. the 79 only has a 300 six cylinder witha 4 speed. its got some power but not like the diesel. ive always loved the older fords...im just wondering what kind of things i will run into with switching the engines???

 

I am not sure what issues you will find regarding pan clearance. I did a '75 F250 4x4 many years ago. I had to trim the front cross-member to clear the pan.

The engine never impressed me much. Not much power and 16mpg tops even with the fuel turned up and timing advanced.

The 6.9 bellhousing will bolt to your 4spd but the gear spacing further hinders the engine.

Mine died due to the cracked block because the P/O plugged it in only after it would not start too many times. I replaced that with a Navistar reman engine that failed from cavitation erosion.

Put a Cummins 6bta in this one and have never looked back.

 

I put a 7.3 IDI and ZF-5 in mine. All in all really pretty straightforward. If your frame is the same as mine, the oil pan will need to all but touch the crossmember. From there build yourself some motormount towers, and away ya go.

 

I had just the opposite experiance and loved it in my 76. It would consistently get 20 mpg if I ran 55 and had lots of tourque. I also liked the gas tranny gear ratios better than the diesels. I could idle off with any thing that would move or it would just sit there and spin at an idle, And put over 300,000 miles on it. I do like the cummins too, but I can't say anything bad about the internationals. The block cracking issue was fixed sometime in 85 and the cavitation is only an issue with some motors after they changed to the 7.3 in 88 so your 86 is good as far as these issues, the only one better is the 87 because it has the 7.3 style rockers but it is a bolt on upgrade.

 

My '84 block had one or more sleeves in it due to erosion. Never tried to determine which hole went bad. I put the 390 back in and sold the truck and engine parts.