Reboring old 6.9 block

[Ethan Smith]

Howdy yall! So i got an old rust block of my buddies ive been tearing apart. Scrapped some good parts off it, but crank burnt up good running low on oil. So anyhow i figured its roughly an 86 or 87 block i went in and asked them to mag the thing for cracks and see about boring it up and having them put in the bottom end for me. The guy at the machine shop tells me its been bored over a couple times and thinks itd be a waste to bore it to a 7.3 because he thinks itl cavitate. Gave me the shpeel on electrolysis and blah de blah. He even said hes never bored one over to a 7.3 so what do yall think? Is it foolish to sink 400 bucks in a good year of a 6.9 block if im risking the **** cavitating?

 

[typ4]

dont go to 7.3 size, bad idea on a 6.9 block. The factory didnt just "bore the 6.9 to a 7.3" Core shift is what caused the 7.3 cavitation issues not overboring.

 

[Thewespaul]

dont go to 7.3 size, bad idea on a 6.9 block. The factory didnt just "bore the 6.9 to a 7.3" Core shift is what caused the 7.3 cavitation issues not overboring.

Russ, you’re saying that a difference in the block composition is the cause of the cavitation issues in the 7.3? I have not heard or read any material that said there was a change in the blocks like that, and have always thought it was the cylinder wall thinkness that was the cause. I’m curious were you are getting that info, it’s new to me

 

[typ4]

Chicago engine plant, met a guy that worked on the IDI line.
Yes they are thinner. So they didnt tolerate core shift. material is the same. Near end of production they made little changes to the cylinder cores. Or so he said. He was in his late 60,s been there his whole career.

 

[Thewespaul]

Chicago engine plant, met a guy that worked on the IDI line.
Yes they are thinner. So they didnt tolerate core shift. material is the same. Near end of production they made little changes to the cylinder cores. Or so he said. He was in his late 60,s been there his whole career.

Interesting info thanks

 

[typ4]

I wish I had all the info we went over on paper. IH made some tough engines.
One thing he did say was the myth of the IDI starting as a gas block is just that. Yes it looks similar in spots but that is for accessory mounting and such.

 

[Ethan Smith]

Holy cow bud, i appreciate the info. I love these engines to death quite literally. Its always nice hearing something new about them. Think its worth pressing new sleeves in or just wait for a better block to come along?

 

[icanfixall]

Holy cow bud, i appreciate the info. I love these engines to death quite literally. Its always nice hearing something new about them. Think its worth pressing new sleeves in or just wait for a better block to come along?

Welcome to the forum. Can you tell us what size the bore is now? We need this information so your question can be answered fairly. If its 30 over you still have plenty of room to bore again.

 

[Runningaford]

There's a company in Spokane, that from what I've seen takes only the 6.9 block, and bores them to a 7.1; I think that's all they'll remanufacture. The name is motorworks, or near there.

 

[snicklas]

Chicago engine plant, met a guy that worked on the IDI line.
Yes they are thinner. So they didnt tolerate core shift. material is the same. Near end of production they made little changes to the cylinder cores. Or so he said. He was in his late 60,s been there his whole career.

Did they make IDI’s at the Chicago plant? Most of the 6.9/7.3 IDI, 7.3/6.0/6.4 PSD Engines were produced at the facility on Broookville Road here in Indianapolis. Not saying he didn’t work on them, just didn’t realize they made them elsewhere.

Unfortunately that facility is almost completely abandoned, since engine production stopped there in 2010. When Ford went in-house on the 6.7 it put that plant out of business.......

 

[Ethan Smith]

So the guy said its bored 20 over already. Im gonna go in and talk after work today. Now i am NO expert at eyeballing the width of a cylinder, but it looks like danm near a quarter in of life at the tip with minimal ridge. Shoulda just shelled out for a bore measure device. I love taking advice from old timers, but itd be nice to have the confidence to just say bore it. I mean as long as theres no pinholes were good eh? I mean the engine did fail from negligence on upkeep, ie. Burnt crank spun bearing, so the jackets could be ready to pop from cavitation? Id just hate to start the hunt again for another block. Although thats my favorite pastime

 

[Hydro-idi]

You won’t find any pinholes in a 6.9 block bored .020 over. Haven’t heard of anyone having cavitation problems with a 6.9 block. They are stout. You got plenty more meat on the bone to rebuild that engine.
If I recall correctly, a stock 6.9 block would have to be bored out 120-140 thousandths which would put it in 7.3 idi specs. Goes to show you how much more cylinder material the 6.9 has.

 

[Ethan Smith]

So i went in. They guy there said its already bored 2 over, probably wont clean up at 3 over, and they need to deck it, and since its probably already been decked im gonna have trouble finding pistons to fit. Im confused, so if a 7.3 is a tenth of an inch over what a six point nine is, whats all the fuss about a few thousanths? Should i just say bring it to 7.3 specs? Or if its been decked and needs a second decking is that now impossible? I really need to start measuring ****

 

[Knuckledragger]

If it has been decked (squared) already, it is not necessary again.

I have .040 over pistons in my truck, I think they even make .060 over. Neither would invite cavitation as much as boring it out .125 just to use standard 7.3 pistons.

 

[Ethan Smith]

So whats with these guys? Theyre acting like this blocks an oily paperweight. Ill just pay them the 50 bucks for cleaning and magging it and either do the work myself or use it as an anchor to my anvil. Maybe theyre drowning in burnt up powerstrokes and cummins from all the turbo happy folk and they dont need the hassle of babying my block