whats the better way?

 

I think the better way was using an engine that didn't use sleeves (or sleeves held together with lock tight) Thats just my guess though. I would think it would be better using a block that can be bored out instead of sleeved.

Just my thoughts though

Adam

 

Yup pretty sure Dave means boring a 6.9

 

The 6.9 block is the better way.

Pistons are available in 20, 30 and 40 over for the 6.9 and then if you want to rebuild again you could always go to the 7.3 pistons at 110 over.

So it would be feasable you could rebuild a 6.9 4 times without using sleeves.

Boring a 6.9 to use 7.3 pistons would be a bit risky, you could cut into a cavitation pocket if the SCA's were not used and maintained on the 6.9 motor.

I am sorry but my opinion of sleeves is a lot like betting 5000 dollars in a poker game using a stacked deck.
You might not lose the first hand, but the odds are against you.

 

Are the walls on a late idi block 93-94 any thicker than lets say early 87-88 blocks. I know of numerous early truck that had cavitation problems but not one of the later

 

87 would be a 6.9 with thicker cylinder walls, 6.9 bore is 4".
7.3 bore is 4.110" and the cylinder wall thickness is the same 88 or 94.

Time and mileage on the older engines gave the cavitation more time to work on the block is the only difference.

 

Sorry i am not trying to high jack this thread but I thought i should post my idea in here.

My idea, that i think would work but not sure, is to mill the pistons down far enough to create an 18.5:1 compression ratio (I am not sure how much is reasonable and safe to take off the crowns on the piston). This would provide a low enough compression to run boost in the 30 maybe 40s. Head studs included. The fueling issue would be left up to dps for injectors and a turbo calibrated pump. My idea though was stolen from the cummins engine that uses a heater grid to heat the ambient air. So in conjunction with a heater grid at the 5" hole on the intake manifold and the glow plugs I would believe it would not be a problem to start in any weather. Might pull a lot on the batteries but two more could be added in the bed i guess.

Anyone think this would work, and i know it could cost a lot of money (most being in the fueling system)

Adam

 

Probally the best thing would be to sleeve a 7.3 down to a 6.9,that would leave plenty of support for the new sleeve,it would now be like a dry liner engine..wayne

 

I can't see why that wouldn't work, I have pistons milled 20 thou and if my truck is sitting in the hot summer sun it will fire up without glow plugs (in 3 turns ususally). I can't help but wonder what trade off there will be with the prechmber though. Normally the profile in the piston top is basically sealed against the head of the engine leaving no place for the gasses to escape out of the prechamber area. With so much space added between the head and the piston, I wonder if burn efficiency will be lost.

 

Duh!!!

only now I understand.....

When you bore out a 7.3L for sleeves, the original bore is completely gone and the sleeve only has what to seat against near the top and bottom of the block. The mitsubisi I described earlier had an actual bore in the block the entire height of the cylinder and THEN a sleeve was pressed in. I can see why a 7.3 sleeved would be unreliable. Why don't they use even a small shoulder near the top of the sleeve that seats into a small counter bore in the top of the block? that way the pressure of the head would actually have something solid to push against when you torque the head bolts down.

Not that I'm an expert or anything lol.

 

Good point David85. I have never thought about that, I wonder if it would even work then. Since you have milled the pistons down on your rebuilt engine has the gas mileage gone down any. I think that would hint at a reduction in burn efficiency, but then again its a new engine and hasn't been broke in. It could also reduce it but not enough to notice it that much. Maybe Dave would know.

Thanks Adam

 

Adam, one thing to consider.

The IDI low end torque and fuel mileage come from the high compression ratio.

If I had any idea that fuel would have doubled in two years, I might not have done mine the way I did.

Yes the power is great.
But I make payments on that power every time I fill the tank.

If that is the route you want to go, be prepared for hard starts even at 60 degrees.
You will pay more at the fuel pumps.
And 80 thousandths off the pistons will give you about 18 to 1.

Dave, that is exactly what I see as being a major part of the IDI sleeve problem.
No solid shoulder for the sleeve to rest on.
That is compounded by the fact that 95% of the fire ring is resting only on the sleeve, putting constant pressure on it.
Run the engine hard, the block expands and the sleeve creaps down farther in the block.

I did check one of my blocks out, the first one I think.
As I remember all of the sleeves were down at least 7 thousandths.
And I believe the two beside the crack were down something like 15 thousandths.

Even if the block did not crack, you have to wonder how long it would take for the head gasket to blow.
I am sure that much movement would be like putting the head bolts in at 1/2 the propper torque value.

 

I opted to mill my pistons mainly because I knew the reman heads I got had been resurfaced and since I was going to take off 10 thou, whats another ten? The idea was to get the compromize between power vs MPG in an engine that would spend the rest of its life with a turbo. Since The OEM compression of 22.5 was set for running N/A, I figured it was a good compromize. I might try to go for a bigger turbo some day, but the truth is I've reached my goal with this truck of 20 MPG @ 70 MPH and I think its time for me to enjoy it now. Its not the most powerful truck on the road, but that was never my goal, even when diesel was $3.50 a gallon (in canada!!!!!). Considering the fact that I used ARP head studs in a 6.9 that rarely hits 10 PSI, I would also like to think that reliability won't be a problem either.

Too bad about the sleeves though, a shoulder would solve the reliability issue and give new life to who knows how many thousands of IDI blocks that are thrown away. Asside from cavitation, the 7.3 IDI was a good engine with a good solid block.

I will eventually have to fix up the body on my truck, but for now everything works well the way it is. The cosmetic part will have to come next, but finding time won't be easy.

If I were to build up another truck the way I did this one, it would probably get rid of the pistons and transmission all together. Too much lost efficiency even in a diesel for me to ignore considering the cost of fuel. I hate buying fuel...

 

Thanks guys for the info, I really appreciate it. I agree with David85, there is a goal we should set for our trucks to reach, and once we have reached it then we should just enjoy it. I was just throwing out my idea to see if it could be done, maybe it could but there would be a lot of time and money of which i do not have either. Thanks again for the great information.

Adam

 

I have to say a little here.

There are many things I could have done to increase the power of my engine even farther that I went, but, I drive my truck every day and everywhere I go.

So when I say the things that I do, I am looking at several things.
1. It has to start, no matter what the temp is.
2. It has to be very reliable, I go to some terrible places to break down or not start.
3. Fuel economy has to be at least reasonable.

So after almost two years, I am happy with what I have built.
1. I have started the engine, not plugged in at 10 below zero. It was not happy, but it did start and run.
2. It starts every time and runs till I turn it off.
3. For where I live, what I haul and tow, how I drive, the things I do with my truck and the places I go I think the fuel MPG is reasonable.

So remember, when I say lowering the compression to 18 to 1 is not a good idea, the reason I say that is because I know it will be very hard to start, even when it is warm outside.
Below freezing, you probably will not get it started, even if you have it plugged in.

If you can't count on your truck to run, that is a problem.
I know few people ever ask their truck to what I expect mine to do every day, and remember mine has been doing it for 22 years, every day.
I did not build it for speed, 85 or 90 MPH is it.
I did not build it for MPG, my average so far this year is 9.87 MPG.
I built it to haul or pull a load, which it does very well.