6.9L Rebuild
Thread Starter
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Freshman User
Joined: Mar 2004
Posts: 31
Likes: 0
From: Cullman, AL
6.9L Rebuild
I know I don't post here often, but you guys will be happy to know that I have decided to rebuild the 6.9L in my 84 F250 dually instead of dropping in the a built 460. Fuel prices... can't beat a small diesel!! 
I'm pretty sure I have a cracked block (it drips when cold, but not when hot) and it has a serious knock.
I'll eventually boost it, so I want to build it so it will handle 10 - 15 lbs boost.
My questions are:
Bolts/Studs: Besides the head studs, should I look aftermarket for main cap and rod bolts also or are the OEM ok?
Pistons: Are the OEM cast aluminum, or are the cast hypereutectic aluminum? I would like to reuse my OEM’s if they (and the block) spec out ok and just get them coated. But if they are just cast, I’ll pop in some Sealed Power Hyper’s.
Coating: Is a thermal coating on a piston top bad for a diesel? I’m going to assume an anti-friction coating on the side skirt and ring lands are ok.
I think I have a good handle on everything else between the OEM manual and hours reading this site. The rebuild won’t be until the late fall, but I would like to start buying parts now.
WISH ME LUCK!! This will be my first diesel rebuild!!
Sorry for such a long post!!
I'm pretty sure I have a cracked block (it drips when cold, but not when hot) and it has a serious knock.
I'll eventually boost it, so I want to build it so it will handle 10 - 15 lbs boost.
My questions are:
Bolts/Studs: Besides the head studs, should I look aftermarket for main cap and rod bolts also or are the OEM ok?
Pistons: Are the OEM cast aluminum, or are the cast hypereutectic aluminum? I would like to reuse my OEM’s if they (and the block) spec out ok and just get them coated. But if they are just cast, I’ll pop in some Sealed Power Hyper’s.
Coating: Is a thermal coating on a piston top bad for a diesel? I’m going to assume an anti-friction coating on the side skirt and ring lands are ok.
I think I have a good handle on everything else between the OEM manual and hours reading this site. The rebuild won’t be until the late fall, but I would like to start buying parts now.
WISH ME LUCK!! This will be my first diesel rebuild!!
Sorry for such a long post!!
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
Sounds like you may need a new block if it really is cracked.
Where is the coolant dripping from?
Early 85 and older blocks were a bit thin in the block heater area, use of the block heater has been known to cause cracks.
If you do have a cracked block, look for an 86 or 87 6.9, much better block.
What do you think is causing the knock?
When you see the size of the main caps, you won't wonder if they should be changed.
I am running stock rods and bolts, no problems.
Head studs are a good deal, the head gaskets will last longer.
The stock pistons are hypereutectic, I used Sealed Power pistons and rings when I built mine.
As for coating, jury is still out.
50% of the people you talk to say good, 50% say bad.
I did not coat mine.
7.3 valves are a good upgrade, the metal composition is better.
7.3 rockers are also a big improvement, bolt right in.
Stock pistons will handle close to 20 PSI boost with head studs.
More boost than that requires a few more mods both internal and external..
Where is the coolant dripping from?
Early 85 and older blocks were a bit thin in the block heater area, use of the block heater has been known to cause cracks.
If you do have a cracked block, look for an 86 or 87 6.9, much better block.
What do you think is causing the knock?
When you see the size of the main caps, you won't wonder if they should be changed.
I am running stock rods and bolts, no problems.
Head studs are a good deal, the head gaskets will last longer.
The stock pistons are hypereutectic, I used Sealed Power pistons and rings when I built mine.
As for coating, jury is still out.
50% of the people you talk to say good, 50% say bad.
I did not coat mine.
7.3 valves are a good upgrade, the metal composition is better.
7.3 rockers are also a big improvement, bolt right in.
Stock pistons will handle close to 20 PSI boost with head studs.
More boost than that requires a few more mods both internal and external..
Thread Starter
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Freshman User
Joined: Mar 2004
Posts: 31
Likes: 0
From: Cullman, AL
Cool!! Thanks for the reply!!
I'm still not sure on the leak, but I'm expecting a cracked block as a "worst case". I've been keeping my eye out for a good 86+ block. It is so hard to see anything in that area with the big honking starter in the way... But I have a steady drip, drip right in line with the heater. But it only leaks when it is cold. Fire it up, drive it for 10 hours and it loses no water at all. Let it sit overnight and it is about a gallon low....
I don't know about the knock. It sounds just like it does a idle, but when the rpm's increase the sound doesn't change on one cylinder. It runs fine, I can loosen an injector on each cylinder and it starts missing, so I don't think I have a dead cylinder. I'm about 60% thinking it is a piston pin knock. But something definitely isn't a happy camper!!
Thanks for the info on the valves, rocker arms and pistons. I'll never be seeing 20 psi, so if my pistons/bores are ok, I'll just clean 'em, maybe coat 'em (more research), and put 'em back in.
It is nice to know that the OEM stuff is rock solid and you don't have to spend a few thousand dollars just to go "slightly built".
I'm still not sure on the leak, but I'm expecting a cracked block as a "worst case". I've been keeping my eye out for a good 86+ block. It is so hard to see anything in that area with the big honking starter in the way... But I have a steady drip, drip right in line with the heater. But it only leaks when it is cold. Fire it up, drive it for 10 hours and it loses no water at all. Let it sit overnight and it is about a gallon low....
I don't know about the knock. It sounds just like it does a idle, but when the rpm's increase the sound doesn't change on one cylinder. It runs fine, I can loosen an injector on each cylinder and it starts missing, so I don't think I have a dead cylinder. I'm about 60% thinking it is a piston pin knock. But something definitely isn't a happy camper!!
Thanks for the info on the valves, rocker arms and pistons. I'll never be seeing 20 psi, so if my pistons/bores are ok, I'll just clean 'em, maybe coat 'em (more research), and put 'em back in.
It is nice to know that the OEM stuff is rock solid and you don't have to spend a few thousand dollars just to go "slightly built".
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
My guess is the head gasket is leaking.
Look at the rear glow plug on both sides, do you see any coolant around them?
Depending on how you park your truck, any leak that goes into the valley pan may show up in the starter area.
Main bearing caps....
Now you can see why the engine is so heavy.
Look at the rear glow plug on both sides, do you see any coolant around them?
Depending on how you park your truck, any leak that goes into the valley pan may show up in the starter area.
Main bearing caps....
Now you can see why the engine is so heavy.
