6.9 OR 7.3 REBUILD

[renegade345]

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

 

[stumiister]

Welcome to the site there are alot of knowelgeable people here so ask away and Im sure someone will answer your questions. I just rebuilt a '85 6.9 and have a 1000 miles on it now the engine is in a '85 F250. Yes the 7.3 has major cavation issuses but the from what I understand is the 7.3 has a better GP system than the 6.9 but the 6.9 block has issues with cracking around the block heater, all of the parts on a 6.9 and 7.3 IDI engine will interchange unless one of them came factory with a turbo, the rods and pistons have bigger wrist pins than a NA engine, I think the heads are also slightly different but I havent seen the heads on a 7.3 so dont know for sure.
The cavation issue can be resolved with the block being sleeved but if you do one hole do all 8 instead that way if a problem does occur you know all 8 holes are good in the block.

 

[Diesel_brad]

Welcome the forum Renegade. PLEASE turn off your cap locks

As far as which block to build, that depends on if your 85 block is an early or late. The early ones had some issues with cracking between the freeze plugs. The late 85-87 blocks were the best

 

[mabc926]

If the 85 in question is your avatar, Then...........More pictures!!

And I would build the 6.9

 

[icanfixall]

Welcome to the forum. Either engine will be a fine build. The 7.3 block can be a turbo block or non turbo block. You wont know til you remove the rods and pistons. The turbo has a 33mm piston pin and all other idi engines have a 28mm pin. As posted, both blocks have issues but nothing we can't work with. A member here was driving a 2000 psd 7.3 and it strated running poorly. Being a company truck it was just take it in to have it fixed... The problem turns out to be 2 injectors went bad so the shop idea is to replace all 8.. Sounds like a good idea.. Till the cost comes out.... $4000.00 to fix it with rebuilt injectors because thats all there supposedly offered anywhere..... I had to laugh at the cost... We can replace set of injectors for as low as $108.. for a rebuilt set of questionable realibility or a new set for around $250.00.... I know what truck I drive and it can be repaired along side of the road in most cases. I'm know to carry a few spare parts behind my rear seat.. Will these engines match the hp of a stroke.. Nope... Not even close.. Can they give a stroke a stroke.. Yes, off the line they haul the beans.. Then the psd gets up some bost and walks away on the higher end. These are a few "things" like porting, turbo, and typ4 cam that helps these engines run better but nothing offered like the psd crowd has. Getting all the cylinders bored true and decking the block and line honing or boreing the mains will give back some hp lost from the factory machining that we get. Look at the rods and mains for wear. If one side shows some wear then that bearing ot cylinder is not true and square to the crank. A ture aligned crank bore thru the main webs will be what you want. Toquue done the main caps and spin the crank with no rods or seals on it. It should spin freely. If it doesn't there is something wrong and your loosing hp due to drag... Hope this helps you along the way. Please ask any questions you want to. No dumb questions on this forum nor is there any childish kicking the cat crap out of anyone for asking a question.

 

[Jake_IN]

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

WHY ARE YOU YELLING AT ME? Other than all that i agree with what Brad said.

 

[Kevin 007]

I would prefer to do a 6.9 over a 7.3.
-I have seen and heard of less valve a guide issues with the 6.9 and I think this is due to the valve seals the 6.9 used, which let small amounts of oil to pass by for lubrication of the guides.
-Cavitation doesn't seem to be as much of an issue with them
-As for the cracking blocks on the "A" motors, you can always delete the block heater and use a rad hose heater or something, thats what I'll have on mine for next winter.
-As for the glow plug issues, im just starting to learn the fundamentals of the 6.9 system vs the 7.3. I recently got a manual switch system working well and now time will tell if it lasts or not. Seems that most member like to switch to the 7.3 controller if they wish to keep and use a controller.
-A head stud kit seems like a popular thing to install if the heads are coming off. I like to practice head bolts re-torquing when I get an idi and then the bolts seems to hold for good. (In my experience)
-The 6.9 fuel filter header seem to be more reliable and not as leaky as the 7.3. Just have to add a better water separator or take care of the factory one.
-The 6.9 had a coolant passage left open whereas the 7.3 had the same passage blocked off for faster heating of the motor, I'd rather have it open.
-And you spoke of lower compression, well the early "A" blocks had slightly lower compression apparently. You may or may not have one. I do, rated at 155hp and its plenty peppy for me without a turbo. More so than my last 7.3 auto. What I wonder about but don't know for sure is if the lower compression is easier on the motors and head gaskets. I like to believe so.

Either way, make sure you use fuel conditioners. One thing I hate about these motors is that the injection pumps just don't seem to last. 6.9 and 7.3 used the same DB-2 pump. I usually run up to 10% bio for lubricity with good results but I won't on my current idi till I get a racor water separator on and a new return line kit. Waiting for spring

 

[Kevin 007]

Oh and I find that the 6.9 starts better in cold weather than the 7.3 and I hear that the pre combustion chambers are slightly different in the two engine so this may or may not be the reason I find them to start better. Thats all I know about the pre-cups....im interested in learning more about them.

And with my experience, the 6.9 seems to be better on fuel. Even my current 84 with the t-19 with no overdrive is getting better mileage than my last to 7.3's both of which had 3.55's and either the E4od or Zf5, which shifted like crap. I have a light foot of course but still. And way better mileage than my 95 stroke that the better half is driving.

 

[Rot Box]

Neither of the two are going to be good to rebuild if you're only doing it to try and impress a PSD owner

Oh and welcome to the forum!

 

[Kevin 007]

Renegade, have you determined if its an early or late 85 block by using the casting number to the drivers side of the injection pump?

 

[George D.]

I love how every one is so quick to say it can't be built to keep up with the strokes in terms of power Hypermax did it so it can be done thers wasn't too reliable or streetable but dominated in truck pulling untill outlawed my point is if someone had the money and was willing to do the R&D I think a happy medium could be reached. How much power an engine can make is more of a question of how much money you have.

My point is instead of saying it can't be done when people talk about building high HP IDIs to me it would be better to tell them they are going to be venturing into mostly uncharted waters and custom parts will probly be necisary and they may run into unknown weaknesses requiring more custom parts. in this day and age if you have the funds you can get anything from custom one off heads to custome rods and cranks. But I don't see a need for either.

The biggest limitations these engine have are the fuel system wich acording to stanedyne engineering documents on the DP2 is only capable of IIRC 32hp per cylinder in an 8 cylinder aplication but hybrid DB2/DB4 pumps can and have been made also 8 cylinder P pumps have been utalised in the past.

If you just want to run with lightly moded 6.0 I don't think it would be that dificult Dave S. on FTE build a 6.9 that could haul more weight up grades than newer truck so should be posible to build one thats faster especial since you are starting with a much lighter more areo dynamic truck even though it doesn't look like it.

 

[Ididriver]

George. Do you have a link to the build on fte?

 

[George D.]

Give me abit I have to dig it up.

 

[George D.]

Here ya go closest thing to a build thread I found on it http://www.ford-trucks.com/forums/512397-well-it-is-not-gray-what-do-you-think-2.html

 

[George D.]

double post oops