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  #1 (permalink)  
Old 03-17-2008, 10:35 PM
ernieselena ernieselena is offline
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6.9 liter diesel

i have a 1986 6.9 liter diesel engine. can i overhaul this motor. i have heard that they are throwaway motors. please advise.
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Old 03-17-2008, 10:43 PM
lazyscholar lazyscholar is offline
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i dont think that they are "throw away motors" recently a guy here rebuilt his 6.9 i'm sure that he can direct you further. The 6.9 were a decent engine from what ive seen, give it a shot
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Old 03-17-2008, 11:57 PM
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CheaperJeeper CheaperJeeper is offline
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I believe you are thinking of the 7.3 as the "throwaway" motor. The 7.3 is a 6.9 that has been bored out 110 thousandths (.11"). Because of this the 7.3 has cylinder walls that are so thin that you really can't bore them out anymore without ending up with cavitation holes in the cylinders. About the only way to rebuild the 7.3 is to have the block bored and sleeved - and even that is a crap shoot since if it isn't done perfectly the sleeves will drop and crack the block.

The 6.9 on the other hand has nice thick cylinder walls (nearly 1/4" of an inch) and can be bored 10, 20, or even 30 thousandths safely - and still have cylinder walls that are much thicker than the 7.3 had when they were brand new. If you are just rebuilding to spec or even to add a moderately boosting turbo - 12 PSI or less - then you don't even need to do much of anything special. Just have the cylinders bored enough to get 'em straight & true, and get OS pistons to match the overbore. Have the crank checked and maybe polished, new OS bearings as needed, and new head bolts, and rework the heads - then put it back together.

If you want to get nuts and go for boost numbers in the 15-20 PSI range (like our buddy Dave Sponaugle), then add ARP head studs, a turbo IP and a set of turbo injectors to the parts list. Maybe add a set of 7.3 rockers to get you a little better valve train.

The 6.9 is definitely not a "throwaway" - a lot of people who have had a 7.3 take a dump on them (cavitation for example) have started with a 6.9 and built a nice motor.
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Old 03-18-2008, 08:12 PM
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ernieselina,
Welcome to FTE and the IDI forum.

The 6.9 is definitely not a through away motor.

Pistons are available in 20,30 and 40 over.
Other than the head bolts, the rest of the engine is fine and the same as a 7.3.
Late 85, 86 and 87 were the best years for the 6.9.

My advice would be a minimum bore, new pistons and rings.
Rebuild the heads as required, pay attention to the valve guides and valve stem seals.
A nice upgrade is to run 7.3 turbo exhaust valves and 7.3 rockers, much better design.
New cam and lifters, new bearings all the way through.

After it is done, you will be ready for several hundred thousand miles again.

With the sleeve issue on the 7.3, many machine shops have a bad taste in reguards to the IDI motor.
If your shop gives you that line, get me a phone number and I will give them a call for you.

I did mine and went a little overboard.
No problems in about 40,000 miles running boost numbers in the mid 20's.
Still getting stronger every day.
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Last edited by Dave Sponaugle; 03-18-2008 at 08:19 PM.
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Old 03-19-2008, 01:08 AM
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I've got about 400 miles on a fresh rebuild for my 1986, and the 6.9 is definatly not a throw away motor. As mentioned, the 7.3 IDI has a thin cylinder wall that cannot be safely rebored (hence the throw away term). It depends on how much you want to spend, but unless there is damage, or other wear that is beyond spec, the pistons, timing gears, oil pump, camshaft and lifters can be reused. These engines have a rollercam, and unless there is damage, they can last indefinatly.

Ideally, you would put a munimum bore in the block to get a fresh seating for the new rings, but that also means new pistons (I ended up with a 30 thou overbore).

I would recomend hot tank and magnaflux for the heads and block just to make sure you have good castings to build on. Inspect the heads to see what condition they are in. If you're lucky, the guildes may still be good, otherwise they should be repaired (lots of oil can be used by loose valve guides).

Upgrades I did include ARP head studs, and 20 thou milled off the pistons. Like Dave mentioned, you can get newer valves and rockers, but it really depends on how much you want to spend on this build, and what your expectations are.
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Old 08-26-2008, 10:01 PM
timberstar timberstar is offline
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6.9 turbo

I've never heard of anyone not rebuilding one
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Old 08-27-2008, 03:26 AM
Dodge/Cummins Dodge/Cummins is offline
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Along these lines what about just putting 7.3L heads on a 6.9L.
I'm thinking it would be a problem to torque the head with the larger head-bolt-holes on the 7.3L
Compression change?
I understand the pre-chamber is different. Does it matter?
Seems to me unless there's a compression change it should work fine. If it's less compression might be a good thing for more boost pressure.
My Dad has a core 7.3 I might steal the heads off of for my future 6.9L build.
On that note is there anything else I should get out/off of the 7.3 NA motor?
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Old 08-27-2008, 10:49 AM
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The seat for the bolt heads is higher in the 7.3L I've been told, so custom bolt/studs will be needed.
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Old 08-27-2008, 12:28 PM
tradergem tradergem is offline
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The head bolts on the 6.9 are 7/16" dia. and the head bolts on the 7.3 are 1/2" dia. and longer.
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Old 08-27-2008, 02:38 PM
Dodge/Cummins Dodge/Cummins is offline
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I've heard the only stud kit for the 7.3L heads sucks.
Plus they're longer and larger in diameter than the 6.9L too, which would complicate the swap.

Sounds like swapping rockers and exhaust valves is the best solution.
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Old 08-27-2008, 05:22 PM
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7/16" bolts are 14 threads per inch
1/2" bolts are 13 threads per inch

Not enough difference in size to re tap the block and get good threads.
The 7.3 has a lower compression ratio.
Since 7.3 valves will fit 6.9 heads, there is no good reason to go through all the headache.
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Old 08-28-2008, 06:31 AM
Dodge/Cummins Dodge/Cummins is offline
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Didn't I hear someone on here talking about getting "all-thread" (grade 8?) from ARP and making there own studs?
One pitfall I see is the "stud" would have to bottom out in the block threads to install them.
Doesn't seem like it would work but if I'm wrong it'd be something I might eventually do to my 7.3L.
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Old 07-31-2010, 07:08 PM
quality boy quality boy is offline
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How much cost???

Quote:
Originally Posted by David85 View Post
I've got about 400 miles on a fresh rebuild for my 1986, and the 6.9 is definatly not a throw away motor. As mentioned, the 7.3 IDI has a thin cylinder wall that cannot be safely rebored (hence the throw away term). It depends on how much you want to spend,
Upgrades I did include ARP head studs, and 20 thou milled off the pistons. Like Dave mentioned, you can get newer valves and rockers, but it really depends on how much you want to spend on this build, and what your expectations are.
with all the goodies, what does this add up to $, ARP's, 7.3 valves & rocker arms, valve job, gaskets, misc. parts disassembly, labor complete?

NO lower end, strait valve job upgrade...Thanks
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Old 07-31-2010, 07:29 PM
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What I did was a medium quality build. No upgraded rockers and while I did use rebuilt heads off the shelf, they are bone stock 6.9 specs. I also did not balance the internals of the engine though I wish I did. Those heads alone cost me $800 before shipping, while the rest of the cost came in at $2200 - all canadian funds. Labor was all my own other than having the block serviced. I say medium build because I didn't go the extra mile to have the internals balanced. At the time I thought it would have been too expensive (but I didn't even bother to ask!!!!!). I also replaced none of the lifters and am still running the original camshaft. All of which might be swapped out this winter depending on what sort of reports come on on that "torque cam" that has been mentioned lately.

Dave Sponaugle built a much better engine and his did cost more. I'll let him chime in with an exact figure or you can drop him a message.
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Old 07-31-2010, 10:31 PM
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It has been long enough that all I can say is I had around 4000 in my build.

That build was considerably more than just a valve job.

Milled pistons and all that.

No labor prices, I also did it all myself, so those were all parts and machine shop work prices.

93 7.3 turbo exhaust valves
Milled pistons
new rings
push rods
injectors
IP
gaskets
bearings
ARP head studs
new oil pump
oil cooler rebuild
maganfluxed everything
Crank polished
Rotating assemby balanced
Minimum bore which turned out to be .030 over.

Already had the new style rockers.
Already had a low mileage cam and lifters.
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Old 07-31-2010, 10:31 PM
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