I am having my 6.9 reworked. I have rebuilt 7.3 heads and was going to use ARP studs. But through error ordered 6.9 studs. My question which set of heads are better. The cost of getting correct studs, drilling and tappin are close to just using the 6.9 studs and rebuilding 6.9 heads. Are there any improvements on heads and problems using the 7/16th studs instead of the 1/2 inch? THANKS ahead of time for any input.

 

I am not sure but I think the 7.3 heads will not fit. The 7.3 has a larger bore than the 6.9 The 7.3 valve train is better and I would use those on the 6.9 heads. So one That knows for sure should be along soon that can say for sure.

 

7/16" x 14 threads per inch on the 6.9
1/2" x 13 threads per inch on the 7.3

If you try to drill and tap new threads, the close hole size and thread difference will mean you will have a junk block.

6.9 heads on a 6.9, 7.3 heads on a 7.3.

Use the 7.3 valves and rockers on the 6.9 heads.
7.3 valves will go in 6.9 heads and you may swap in that direction, I used 93 7.3 turbo valves in mine.
7.3 rockers are a direct bolt on swap.

 

I'm curious why you can't use the 6.9 ARP studs in the 6.9 block with the 7.3 heads. Do the bolts align the head or do the alignment dowels do that. Or are there water passage/head gasket differences?

Not arguing or anything, just trying to understand because I'm in the same boat as the OP: known good 7.3 heads, and rebuilt 6.9 short block.

 

Head bolt sizes are different, the 6.9 uses a smaller head bolt than the 7.3. I was thinking there were some conversion studs mentioned before...

 

hes wondering if the 7/16 stud in the 1/2" head hole would be a problem.

 

Considering it would leave a gap, yes... When you recall that these motors run in the range of 24:1 compression, the ability to leak is not a good thing. The lineup dowels are not locators, in that they aren't designed to keep the head from moving, and are probably smaller on the 6.9 due to the smaller bolt size as well. I would not be comfortable with just the clamping force only to locate the head...May not be much movement, but it is still there.

 

Well just an idea. Could it possibly work if you get a machine shop to custom fab some sleeves to take up the extra space in the bolt holes. Customize one for each hole to ensure proper height so that the studs clamp down properly. Not saying it WOULD work, just a thought.....

 

That might work. Make them a bit shorter then the thickness of the head so that the studs clamp the head and not the tubes. The worst that could happen is you might pop a head gasket.

 

Hardest part would be making sleeves that thin... 1/32" wall thickness is not much to work with.

 

I agree that a sleeve would be best but since the head bolts already have a gap between the bolts and the heads I don’t think the sleeves would be necessary. (They already have a gap or they wouldn’t be able to be removed. It’s not like the head bolts are a press fit).

To my knowledge, the head bolts simply provide clamping force, not alignment. That is what the dowels are for. I talked to my machinist and he said there a lot of engines running around out there with 7/16 bolts in heads designed for 1/2" bolts and that the alignment dowels are what locate the heads on the block.

Granted, he’s not a diesel expert, but he does build some extremely powerful gas (NHRA) engines.

I was doing some research and remembered about 351W heads on a 302. Edelbrock makes “T” washers designed specifically for what we're discussing (using 7/16 bolts in a head designed for 1/2" bolts):
Edelbrock.com - Cylinder Head - Accessories
Head Bolt Bushings #9680
"Complete set of head bolt bushings allow the use of stock 7/16" head bolts with Edelbrock heads. Required for 289-302 V8s and 1967-69 AMC. "

The only question I don’t know about is if the alignment bushings are the same or what their actual sizes are and then of course if there are any head gasket differences.

I’m just passing along what I found and not making any claim that it would or would not work.

 

If it helps, the alignment dowels are 5/8" o.d. on an 87 6.9 block/head.

 

So the alignment dowels are the same on 6.9 and 7.3 and the head gasket are the same.5/8" on the 7.3.

 

The head gasket itself is not the same part number, and there are some visual differences. Can't answer if the alignment dowel is the same.

 

I vjust mesured the 7.3 dowels and they are the same,and for the head gasket if you get the 7.3 gaskets they should be larger at the head bolts and at the cylinders.