Short block 6.9 will take 7.3 heads???

[h2odrx]

i saw this and just was wondering??????
short block

 

[TLBREWER]

I don't think so. Head bolts for sure are different sizes (may be able to drill/re-tap) and I think there is a difference in the head cooling passages.

Tom

 

[argve]

The heads will fit but as stated the head bolt size is different - 1/2" vs 7/16" on the 7.3 the head bolt diameter was increased. The coolant passages if I'm not mistaken are blocked off on the 7.3 head but they will bolt on if you can get the bolt issue taken care of...

 

[Full Monte]

Mel also told me on another thread they'd fit. All you have to do is drill the head bolt holes larger.

 

[Mr_Roboto]

Mel also told me on another thread they'd fit. All you have to do is drill the head bolt holes larger.

That is for fitting 6.9L heads on a 7.3L block.

I beleive the eBay seller was a little overzealous in insinuating that the 7.3L heads would bolt onto the 6.9L block. It can be done, however spacers would need to be machined to take up the extra space, or else custom studs would need to be made with 7/16" thread for the block and 1/2" thread for above the block.

 

[h2odrx]

that is what i was thinking? maybe i'll ask him?

 

[Mr_Roboto]

There has been discussion of drilling out the 6.9L BLOCK holes to fit 7.3L bolts / studs. The consensus is that it cannot be done because there is not enough difference in size between 7/16 and 1/2 thread to remove metal all the way down to the 7/16 thread root. Basically when you re-tapped you would end up with as much air as metal for thread.

 

[f-two-fiddy]

So can we bolt 6.9 heads on a 7.3 block?

 

[icanfixall]

No 6.9 heads are drilled for 7/16 bolts and the 7.3 block is 1/2 inch bolts so they will not fit. If you try drilling out the heads that may take off way too much metal and enter a water jacket.

 

[LUCKY_LARUE60]

I talked to a machine shop about putting 7.3 heads on a 6.9 and what they told me was YES it can be done with no problems. The guy I talked to has a 93 7.3 and his dad has a 6.9 and as we talked he told me to do this I could to put bushings in the head bolt holes but it was not necessary. I asked about head movement and he said the alignment dowels would keep them from moving and also the fact the the intake bolted to both heads would also keep the heads from moving. He said the clamping force of the head bolts was enough to keep them in place. Also another suggestion about the head bolt was to have head bolts made that had the same thread count as the 6.9 but 1/2 inch and re tap the threads in the block of the 6.9. The main reason you can't drill and tap the 6.9 block is the thread count is different on the 6.9 and 7.3 head bolts and if you can't get enough threads if you drill the 6.9 block to take the 7.3 bolts. Here is the head bolt spec's

Cylinder head changes
Cylinder head bolts - 6.9 = 7/16"-14 UNC 5.25" long
Cylinder head bolts - 7.3 = 1/2" - 13 UNC 6" long
Cylinder head bolt washer 6.9 = .105" thick
Cylinder head bolt washer 7.3 = .134" thick

Just some input

Jim

 

[dsblack]

I bought a set of heads for my 6.9 when I had it. Got a great deal. The machine shop started rebuilding them, and drilled the holes for a 7.3 guaranteed that it would be ok with the 6.9 bolts.
Ran it for a year before getting the crew cab. Never had an issue. So I think you would be ok.

 

[Mr_Roboto]

Yes if you had special high grade bolts made it would work, as long as the thread root followed the old thread. However that mean machining and tapping the block, plus the cost of the custom threaded bolts.

I think that using special studs would be cheaper and easier.

If the positioning dowels are indeed the same size on the two engines, then the 1/16" difference in bolt size wouldn't matter, since it is the dowels themselves that position the heads.

 

[icanfixall]

Sorry Lucky... That wont work. If I'm reading correctly what you are thinking is fabricate a bolt that will fit the 6.9 heads but have the threads be 1/2x14 so they match up??? No way will they fit thru the heads. Now going the other way and fab up a bolt that is 1/2 inch body but has 7/16x14 threads will work but now your back to the same issue we have with the small 6.9 bolts but just down at the threads... Where it will for sure break....

 

[Mr_Roboto]

Why would a 1/2" x 14tpi be any larger than a standard thread?

 

[Doc]

What does it cost to have someone fabricate new holes for the head bolts? Seems as though you may not be saving much in the long run. Also, are all the mother mounting holes for things like exhaust and other stuff under the hood the same for the 7.3 as the 6.9?