1983 6.9

What’s up guys? I’m new to the idi platform and diesels in general I want to build a idi to put in my 75 f250 for simplicity and for reliability and fuel millage compared to my tired old 360. I have a 7.3 block but I don’t trust that the previous owner of the engine took care of it properly and I doubt it had SCAs added to it so I’m worried the cylinders will be worm holed. When I drained the coolant and oil it was completely milk shaken. I have an opportunity to buy a 6.9 with really low original millage from a buyer I trust for $150 for the complete engine. I have read that the block heaters can crack the block as well as differences in heads throughout the 6.9 run and compression ratios. I’ve got a few questions regarding all that

a) is that the extent of the block weakness

b) I’ve read that there’s a difference in the head precup design but I haven’t been able to talk to anyone to confirm the difference nor to find out if later model 6.9 heads will be compatible

c) I’ve also read that the 83 6.9 had lower compression (20.5:1) than later years (21.5:1)… is the difference in the piston, deck height, or combustion chamber to account for the lower compression.

I’d like to have as much compression as possible to aid in starting if I can’t use the block heater as I know these motors are cold blooded.

d) Is the 83 6.9 even worth building or should I find a later year.

I’m aware of the difference in head bolts I’m not too worried about that because I do not plan on boosting the engine I’d rather have the thicker cylinder walls from a 6.9. I do however plan on using the serpentine accessory drive from my 7.3 as well as the better glow plug controller regardless the engine I end up with

Thank you guys

IDI highboy said:

reliability.

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Early 83 "A" blocks are rumored to /maybe/ crack around the block heater. When I asked about it I was told if it was going to crack it would have already. I daily drove mine (A block) for years and used the heater in the middle of winter at -20 with no problems.

89Laredo said:

Early 83 "A" blocks are rumored to /maybe/ crack around the block heater. When I asked about it I was told if it was going to crack it would have already. I daily drove mine (A block) for years and used the heater in the middle of winter at -20 with no problems.

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Gotcha gotcha, I wonder what the time/millage frame was for that… the engine only has 60k miles on it then the truck was T boned instead of repairing the body this guy was going to swap it into a gasser truck he had. but life happened the kids were born and the motor sat his barn up until now, he still drives the 460 truck with the 460 in it. I recently went to fix his air conditioner and we got to chatting when he saw my 75 and he offered me the engine. All that said the whole “if it was going to it would’ve by now” thing makes sense on an engine that seen a whole life but this one was retired before it had seen much life.

IDI highboy said:

is that the extent of the block weakness

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Yes.

IDI highboy said:

I’ve read that there’s a difference in the head precup design but I haven’t been able to talk to anyone to confirm the difference nor to find out if later model 6.9 heads will be compatible

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I don't know about the precups, but if you're asking if the later 6.9 heads will fit on you 83 block, the answer is yes. I would recommend checking the flatness of both the block and the heads before installing.

IDI highboy said:

Is the 83 6.9 even worth building or should I find a later year.

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I'm not sure what you mean by "building", but it would be worth using.

IDI highboy said:

I’ve also read that the 83 6.9 had lower compression (20.5:1) than later years (21.5:1)… is the difference in the piston, deck height, or combustion chamber to account for the lower compression.

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I'm also not up on the reason/cause of this, but it may be the precups. Just a guess though.

IDIBRONCO said:

Yes.

I don't know about the precups, but if you're asking if the later 6.9 heads will fit on you 83 block, the answer is yes. I would recommend checking the flatness of both the block and the heads before installing.

I'm not sure what you mean by "building", but it would be worth using.

I'm also not up on the reason/cause of this, but it may be the precups. Just a guess though.

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By building I more mean the whole process of buying tearing down and refreshing. I’d rather have a 100% new engine as far as bearings and seals and rings than a 60k miles/43 year old one. Thank you for your response it’s very helpful. Can you confirm if the difference in compression exists?

IDI highboy said:

60k miles/43 year old one.

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Making' us feel old
Compression should be the same.
Just to throw my 2¢ out there, my 7.3 is out of a 1988 and running just fine, completely stock and original bottom end, only recently did I do head work and a few other goodies for more ponies. You'd probably be fine on just sending the 6.9 as she is.

Nero said:

Making' us feel old
Compression should be the same.
Just to throw my 2¢ out there, my 7.3 is out of a 1988 and running just fine, completely stock and original bottom end, only recently did I do head work and a few other goodies for more ponies. You'd probably be fine on just sending the 6.9 as she is.

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I’m jealous yall lived when vehicles were mechanical and you didn’t need a doctorate degree in computer engineering to work on them …. i know it’s probably fine to stick in the truck as is, however it’s not going to be an over night project as I also want to find a snow fighter front axle. because I don’t trust the closed knuckle Dana 44hd on 37s as is, let alone the added weight of an idi vs the FE engine that’s currently in it. So if I’m waiting to find a snow fighter or saving towards one I’ll have ample time to put a motor together in the garage and take the extra time to paint it all pretty even tho it’ll be dirty in no time. I’d like to have a motor, transmission, axle, suspension and what not all sitting before I tear apart my running driving truck. Not to mention, parts are available now from the research I’ve done there a few company’s that make solid high quality parts but support for 6.9s seem to be diminishing for example pistons are hard to come by now and who if r&d had a change of heart tomorrow (not that he will obviously) and decided to pivot towards 7.3 power strokes then I’d at least want to buy parts and build an engine while I can.

Remember when ya paint it all pretty, by the time everything is on it all you can see is the valve covers and the oil pan so pick a good color for those

DougBoy66 said:

Remember when ya paint it all pretty, by the time everything is on it all you can see is the valve covers and the oil pan so pick a good color for those

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As sacrilegious as it sounds Chevy engine orange… it’s almost the same color as my truck and it’s easy to find cheep.

IDI highboy said:

Can you confirm if the difference in compression exists?

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Nero said:

Compression should be the same.

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A quick glance at Goo gle says that there is lower compression on the 1983 and maybe some 1984 (there's differing answers of course) 6.9s is lower. There may be something to the years since it was probably the A blocks (guessing by the years) that had the lower compression ratios.
The only tricky thing about the A blocks is that they use pressed in piston cooling jets. They can be removed and reinstalled, but it's just not as easy as the bolt in ones on the B blocks and the 7.3s. At 60,000 miles, you shouldn't have to worry about pistons. A rering should be just fine.

IDI highboy said:

if r&d had a change of heart tomorrow (not that he will obviously) and decided to pivot towards 7.3 power strokes then I’d at least want to buy parts and build an engine while I can.

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I doubt that there's much danger of that. Justin's a pretty dyed-in-the-wool IDI guy. They are his whole business.

IDI highboy said:

sacrilegious as it sounds Chevy engine orange… it’s almost the same color

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I did this, so orange is cool with me not exactly factory color but close if your color blind

IDI highboy said:

As sacrilegious as it sounds Chevy engine orange… it’s almost the same color as my truck and it’s easy to find cheep.

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Now that I remember it, I bought my first Dent Side from a friend who rebuilt the engine while he was driving it. He painted it what he called Ford red. I used to call it Chevy orange to dig at him a little bit. It did look really similar to the orange paint.

Heres all the info you want for A vs B.


Looks like 173828 is when they strengthened the block. Quite a bit after the A vs B serial break at 59209.