I am looking into rebuilding a engine for my 94 f-250 with 4.10 gearing. Which is a better engine for rebuilding. I will do all the work myself. And I have the factory turbo set at 12psi to bolt on. The 6.9l has a smaller bore and probably makes power at higher RPM to complement the 4.10 gears but the blocks have prblems with pitting. Any suggestions?

 

I think if you read back you will find the decision is the newer casting 6.9L blocks are the way to go... there was a post a while back showing were this nubmer was cast, and which ones were the good onss compared to which ones were bad... If im not mistaken it was late 85-87 were good... the mid 85s and older were the not so good?? My memory is not always the best

The 7.3Ls have a much thinner cylinder wall, makeing boreing risky. ANd if you read some of Dave S's adventures, you will think twice about a re-sleved block.

The 6.9L can safley be bored making it a much better choice for re-building...

Im sure Dave S will be along to share his wisdome, he seems to know this question inside and out..

all the best!
Bob

 

I'm going to agree that a 6.9 is more re-buildable than the 7.3 just because of the bore issues. I like the 7.3's bolt on piston cooler nozzles tho. The 6.9's were a drive in nozzle that was a pain to knock out and re-clock on install.

 

Sorry I am running a late 85 6.9 block, has a counter bored block heater.
The casting number I forgot long ago.
The piston jets are bolt in.

A 7.3 is a 6.9 bored 110 thousandths.
Heads had 7/16" head bolts on the 6.9.
Heads had 1/2" head bolts on the 7.3.

To reliably run boost higher than 10 PSI I suggest head studs.
Also mill the piston tops to drop the stock compression a little, then you can run more boost.
Use 7.3 rockers, they are stronger.
Magnaflux everything.
Run 93 or 94 7.3 turbo injectors and IP.
Do not skimp on parts, get good stuff.
A machine shop that can do excellent work is also a must.
Balance the engine rotating assembly, to over 4000 RPM.

Take your time assembling everything, check it three times.

Take your time breaking it in, vary the engine speed constantly.

Mine is bored 30 over and the cylinder walls cleaned up perfectly.
It runs strong and is getting better every day, I have 8000+ miles on it now and I think the rings are still seating. Fuel mileage is increasing and so is the power with every tank of fuel that goes though it.

7.3 cylinder walls are to thin already, cavitation is a real issue because of it.
Although they sell oversized pistons for the 7.3, I would not even think about running them.
When I bought a reman 7.3 engine I blew three up under warranty, the sleeves were the issue on all of them.
They sent me a fourth engine, which I tore down while it was still bolted to the shipping pallet.
The sleeves had all dropped in the block and the engine had never been fired, I refused to install it.
Took a couple months, but they finally bought me out on the engine.

No sleeved engine will ever again will go in my truck, so that leaves the 7.3 out.
Throw away engine block when it needs rebuilt.

You could possibly rebuild a 6.9 two or three times if you can find a good machine shop.
The one I chose builds a lot of race motors.
They also had had bad experiences with the 7.3 engine and did not want to do the machine work for me.
After I explained what I was after and why I wanted it done the way I did, the owner said I may be onto something, so he agreed to do it with no guarantees.
I told him I wanted to do a minimum bore, just enough to clean the cylinders and no sleeves. I also told him if he did what I wanted, I did not need a guarantee.
So he agreed and did exactly what I wanted.
When I took the pistons in and told him to shave 50 thousanths off the top, he thought I had gone off the deep end, but he did exactly what I wanted as per our deal.

I see him every couple of days out on the road and I drive up the hill in front of his house every evening on my way home.
He is impressed with the way it runs out on the road.
He is not so impressed with the black smoke when I take off from the stop sign by his house. I do lay into it a little harder just for him though.
But then he was impressed when I told him I was running over 20 PSI of boost to it.

He told me the other day he would rebuild another 6.9 if it could be done like I did mine, I have convinced him it is the right way to go.

 

What about the heads. Any Mods? 7.3 heads dont work do they? And did you use 7/16 studs or tap the block for 1/2" studs for added strength? Do you recommend just reconditioning a low milage engine (rings and bearings). My engine only has 250000km on it. Runs great only it has 3 pistons with 7/16 long cracks in the valve boss in the piston.

 

Threads are different.
7/16" x 14 UNC
1/2" x 13 UNC

The 7/16" threads would make the 1/2" threads real weak.
I used 7/16" studs from ARP.

That is a somewhat tough call to make.

Without honing the cylinders you replace the pistons in the rings will take forever to seat. But if you have much wear in the cylinder wall, they may not seat anyway.
Boring is not an option on the 7.3 without installing sleeves.

I have about 4500 in the engine I built, but I did go to excess in some peoples eyes.

I depend on my truck, drive it about 800 miles every week.
If it were me, I would have to take it to a machine shop and make sure it was worth rebuilding. Check the cylinders for out of round, taper and grooves at the top and bottom of the stroke. Then you will know if it can be honed so the rings will seat or if it is to worn for that.

Finding a 6.9 and then rebuilding it would get a little expensive.

 

Too bad you're not in BC, polish. I have a spare 6.9 that just needs a head gasket I could sell you for a real reasonable price.....

 

Question re resleaving the 7.3, Dave, do you suppose that sleeves slipping were just poor workmanship by the overhaul shop, or does it have anything to do with turbo boost. Seems to me that many diesel engines are built with sleeves right from the get go, so is a sleeved 7.3 really all that bad an option if were done right? As the 7.3's start getting higher milage, I'd like to think it could be satisfactory rebuilt without trying to go find and even older 6.9.

 

Cheeper I thought all this engine needed was a set of headgaskets untill the heads came off. And there are lots of 6.9 and 7.3 around for very good prices but I will probably end up with the same thing. But for the right price on a knowen good engine the coast isint that far from Red Deer Alberta.

 

The problem with these sleeves they're putting in, is that they are held up by a small lip they leave 'unbored' at the bottom. This lets the sleeve crush down a bit when you torque the heads on. I did a shortblock for a guy a couple years ago. You wouldn't believe all the popping and cracking sounds those things made as I torqued the heads. I was sure it wouldn't last, but it's still going. It's got an ATS on it too. I figure it'll last another few years tops, but that's what the guy wanted to do.

 

Well, what I know for sure about this engine is that it was bought in July this year from a local wrecking yard - I have the reciept that says "guaranteed rebuildable core". But even then I wouldn't sell you a pig in a poke! If you wanted I could be persuaded to pull the heads to make sure the pistons aren't cracked.

If the piston cracking is is due to EGTs - as seems to be the expert consensus - I'd think that would be a lot less likely with this one since its a non-turbo.

 

The sleeves that the medium and heavy duty trucks are different than the onews used on the 7.3 block. The others had the block bored from the factory to have removeable sleeves, and there are 2 styles, dry and wet. The dry sleeve is practically press fit, but there is still a lip at the top to keep it from moving in the bore. The wet sleeves have o-rings at the bottom of the sleeve on the outside, and the coolant actually is in contact with the sleeve itself. The o-rings are there to seal the sleeve to the block. Those sleeves actually stick up above the deck and seal to the head.
It sounds like the sleeves they are putting in the 7.3 block, which were never designed to have sleeves, do not hav the lip at the top to keep them from sinking in the block. That would solve the problem of shifting if they did that, but it would seem they do not.

 

Actually when you bore and sleeve a 7.3 block, you usually end up with a wet sleeve on #s 7&8. I've had 2 done and both bored into the water jackets. My machinist has done many of these and leaves about 3/8" in the lower bore for the sleeve to rest on. Both of these engines have run in excess of 150K with no problems. I rebuilt one several years ago that had .020 pistons from the factory. It had little wear in the cylinders, just a broken crank. These were a one year only piston and there were no rings available for them, so I had to bore it to .040. I was almost afraid to fire it off at first (sonic testing read one spot that was only .073" on #8), but it has over 200K on it now in a F450 wrecker.
Jeff

 

So it sounds to me like it is very possible to do the job right with a shop that knows what their doing and achieve a satifactory rebuild on a 7.3 with sleaves. Same old story, fast and cheap isn't always best, even in engine machine shop. Plus I guess it's hard to find knowledgable experianced people these days.