1975 f250 6.9 rebuild

So I swapped this engine in and got it running about a year ago. And it’s done everything I asked it to great, except for a couple times the Cali heat has gotten to it because I cheaped out and bought a 2 core aluminum rad instead of the 4 core option and it costed me a head gasket.

It is currently setup with a typ4 camshaft and arp studs with a stock injection pump and injectors fed by a Holley blue fuel pump.

for the next engine I plan to take an old 7.3IDIT my buddy has laying around and send it to the machine shop to be sleeved down to a 6.9. I want to do this for the the thicker cylinders and 1/2 inch head studs. I also want to run 6.9 heads because of the bigger pre-combustion chamber. Can they be drilled out for the 1/2 inch studs or would I be better off with a 7.3 head and not bother with the bigger chamber port? I plan to turn in the turbo rods to Justin at R&D for a set of powerstroke rods, I haven’t really figured out my fueling or turbo setup I want to go with though. Any input would be great to hear, the truck has 37” tires and 4.10 gears, a zf5 and it weighs about 6800 pounds.

Dream build man. Love that style and driveline setup. If you use 6.9 heads swap the rocker arms from the 7.3 on the 6.9 heads

Thank you man, I’m only 19 and to already have built my dream truck is definitely a great personal achievement. I actually already have 7.3 rockers on the current 6.9 heads, did that too when I first put it together.

You'd be fine to have the bolt holes in the heads drilled our to 1/2" as long as they are straight. I still have to wonder about the in-cab fuel tank. I had two 1975s and neither one had a tan inside the cab. Maybe it was a mid year thing and mine were later builds? If I could find another dent side for a reasonable price, I'd IDI swap it for sure!

Everyone’s theory on the in cab tank is if you get hit hard enough to have to worry about the tank rupturing AND finding a way to light off DIESEL is you’ve got other things to worry about like the fact that the cab would have to be pushed passed the steering wheel to get into the tank. And yeah in 76 they went to no tank in the cab and my truck is a June built truck so technically it’s just before that mid year production mark that ford always likes to change stuff on. And I’m not sure where you’re at be here in nor cal there’s dents everywhere for cheap. Of course there’s the guys asking an arm and a leg for a rusted out shitbox but that’s usually the younger guys.

The 6.9 heads don’t have a larger prechamber it’s actually about 11.5cc smaller than the 7.3s, and even smaller in the A block heads which are pretty rare. I would save your money and run the idit rods instead of the psd rods, they are both pretty much the same strength.

Hmm somewhere I read that the 6.9 heads have a larger opening on the prechamber, I’ll take your word for it though. And the rods ARE the same strength or are they ALMOST the same? I want the strongest possible rod I can get.

carsonlhammond said:

And I’m not sure where you’re at

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Northwest Kansas. I can understand why they're cheap, especially if they've been sitting for a while and the taxes weren't paid. Here, the state understands that you can't be held responsible for taxes that someone else didn't pay. I could buy the crew cab dually that I drove by yesterday (it's been sitting for at least 11 1/2 years) and even if the taxes weren't paid, I wouldn't have to pay them because it wasn't mine.

Had a buddy come over last night and by pulling the studs we were able to get the head off in the truck, had to unbolt the booster but only just barley. One stud in the back wouldn’t come out of the block so we still had to lift over it. And of course it was the one below the booster right next to the exhaust port on number 5. How does this piston look to you guys? When I took it apart last time I didn’t remember that heat marking in the tops of them, they all have it. Plans have changed and now I’m just trying to get this engine back to running condition so I can start on my hybrid block.

That seems to be fairly common. I've seen it on quite a few engines. I don't believe that it's "heat" markings, but since I don't have an explanation, I very well could be wrong. Hybrid block? Please elaborate. It sounds interesting.

By hybrid I mean 7.3IDIT crankshaft, powerstroke rods, and a 7.3 block sleeved into a 6.9. That gives me 1/2inch studs but thick cylinders and insane amounts of rod strength. I’m not planning on building a monster amount of power I’m just looking for insane reliability at like 300 crank hp without the front dress and everything.

carsonlhammond said:

I’m not planning on building a monster amount of power I’m just looking for insane reliability at like 300 crank hp without the front dress and everything.

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Well that sure ought to last about forever.

IDIBRONCO said:

Well that sure ought to last about forever.

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That’s PRECISELY my goal lol

I’ve personally never seen this before so not that I don’t believe you IDIBRONCO I just would like for someone else to chime in about the white stuff.

Don’t know for sure but could it be incomplete combustion?