I'm in the process of building a custom 1956 F600 4x4. I still need the axles and tires I want to really get going, but here is how she sits now:



After 2 or 3 years now I think I have finally decided on a powertrain route, and I think the 6.9 IDI is the way to go. I'm still fairly new to the IDIs, and most my experience in the past has been with gas engines, but I'm learning quickly. From what I've come across they are extremely reliable and easy to work on. I like the idea of also being able to run WVO on it quite a bit.

From what I've come across the '87 is the 'best' one they made, though I imagine if I come across a good 7.3 I might go that route. I'm not sure if there are any real differences as far as fitting them (From what I've read a 7.3 is a bored out 6.9, but I don't know if say there might be years which the transmissions don't bolt up the same or what not). I figure if I can get a decent one cheap and get it set up, if I ever need to I can swap it out with another pretty easily. From what I've seen the 6.9 from 1987 should be the most reliable and I should be more likely to find a good one over a 7.3 that has more of a Cavitation issue.

I figure I will check to see how I like it without a turbo, and in time when I have the extra cash probably throw one on there. I'll probably look into what works that doesn't have to be newly bought.

On an interesting note, the IDI seems to sound a great deal like the Y-block that is currently in my truck (that gets about 5mpg), a bit of a plus.

So hopefully you'll be seeing more of me when I can finally get rolling on this build

 

Sounds like a neat project! Remember, we like tons of pics!

 

Thanks

Ton's of pictures I do, the vintage truck group loves them as well, including myself.

Do you know of anywhere that shows the differences in the years? I'm coming across a wide range in my search but I'm not all sure what would make one better than the other if I had a toss up.

Thanks

 

I believe 84-87 is the way to go, they worked the early kinks out, most the the 7.3 strengths are built in, and it's pre-cavitation issues. All the upgrades that the 7.3 sports, studs etc, bolt on, or with minimal tweaking at most. And the 10-15 hp or so you lose choosing the 6.9 over 7.3 is negligible when you put a turbo on it.

Find a running later year 6.9, get the entire thing rebuilt (and possibly beefed up) and you'll be laughing as she runs forever.

 

Sounds like a neat build.

Dig the avatar too. One of my favorite shows

Jason

 

About what does a rebuild on one of these run? I'm all for doing it myself so I can really learn the engine if it's not too crazy (from what I've gathered these are "simple" engines). Any good places to find parts?


Seems a whole lot of people on here are near my next of the woods (currently Sheridan,WY, I'll be moving but I like mountain country). Just odd to me as there is maybe one or two people within 500 miles of me in the vintage truck section. Kinda nice, lol.


About what can I expect to pay for a 6.9? I've seen what looks like a decent deal on craigslist around here for them, maybe $500 or so. I think I would benefit from a full donor though, especially a F350 4x4 so I can have a dana 60 up front and all that parts I need for my build. I've seen them with a 6.9 for about $4000-5000 lately, but I can part it together for about half that. Maybe I'll start asking around once I can really get to buying parts, unless you know someone wanting to trade for some hand forged Damascus knives, lol. (I'm a professional blacksmith)

Thanks

 

If you were closer I have 2 6.9s for sale... For a good condition low mile 6.9 most I'd pay would be 500-600. I bought a factory turbo idi 7.3l for 800... These engines are simple to build just be aware that they are heavy so any hoist or stand you use make sure its worthy

 

Try to find a 6.9 model 84.5 and up if you plan on using the block heater at all

 

Actually make that 85.5 and up for the block heater.....


For those who don't know, the earlier blocks, tend to crack at the block heater freeze plug location ONLY if the block heater is used! Doesn't mean it will happen, but the chances are there....


83-85 have that as a negative point.

83-86 has the older, not so great glow plug system

83-86 has weaker rocker arms

1987 only has Solid state glow plug system (same as any 7.3), 7.3 style rockers, less chances of cavitation.


And 1 thing I like better about the 6.9 over the 7.3


The 6.9's have better head and block cooling.


If you've seen 6.9 heads, beside 7.3 heads, you'll notice on 7.3 heads, 2 big coolant passages at each end (2 per head) are blocked off, while on 6.9 their open, for cooling.

It's much easier to heat up a 7.3 than a 6.9.




So that's a little something to keep in mind.

 

Oh and also...

 

Thanks, I was curious on what the differences where with the years. I'll keep an eye out for an '87. Nice to see they are fairly cheap, back when I was looking at a Cummins it was always $1000-1500 for a cheap one.

I find it interesting that there always seems to be that one year for everything, heck even my truck only looked like it did in '56.



Anyone have a guess what I can expect to sort of see for fuel mileage? I'm currently unsure of what gear ratio I will be running (all my plans where for gas engines and they are to rev a lot higher on the freeway), but I would want a manual. I would be running 37" wheels and I'll be around 4,000-5,000#s depending on what all I do.


Also, does anyone have a way to identify a 6.9 from 87 easily? I guess the glow plugs would be a good sign, I'll have to look into that to see the difference. And if I remember right the 6.9 had 7/16" bolts on...crap I forgot where, lol. Just remember the 7.3 had 1/2" ones.

 

Yes headbolts, here is a size difference pic

 

Another easy way.


Heres my '87 6.9

It will have a glow plug controller that looks like this with 12V bullet glow plug connectors.


The 83-86 6.9's had 6V spade connector plugs and a controller that screws into the drivers side head like so.






Now to identify a 6.9 from a 7.3

All 6.9's have a separate water separator.

The 7.3's have it screwed under in the fuel filter.

And like already said, the head bolt size is also a giveaway.

 

Thanks for that, much easier to understand when I can see the difference like that. Where would I find the 6.9 water filter?

 

I know the 83-86 trucks, it's mounted on the drivers side firewall, but i've never seen under the hood of an '87 6.9 truck. Might be there also, but not sure.