Machine work on 6.9 heads??
Thread Starter
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5th Wheeling
Joined: Dec 2007
Posts: 41
Likes: 0
From: Santa Clarita, California
Machine work on 6.9 heads??
This is my first posting here, although I have been very pleased with reading many posts and the information provided.
I Recently purchased two trucks.
A 1986 F350 crewcab 4x4 with the non turbo 6.9 and the C-6 transmission.
A 1986 F250 regular cab 4x4 with the non turbo 6.9 (thrown rod through the pan...ouch) and the C-6 transmission.
My questions are related to the regular cab truck which recently had the heads rebuilt. The previous owner stated that the valves were done and the heads were milled. From my experience working on gasoline engines, this could increase the compression slightly. Would it have an inherent bad affect on the deisel which is already at 20 to 1 or better compression? Could this have caused the engine to throw the rod? I purchased the truck with the thrown rod.
How can you tell if you have a lower end knock? My crew is very loud to begin with, let alone trying to hear a knock in the lower end.
Any help would be appreciated.
Thanks
I Recently purchased two trucks.
A 1986 F350 crewcab 4x4 with the non turbo 6.9 and the C-6 transmission.
A 1986 F250 regular cab 4x4 with the non turbo 6.9 (thrown rod through the pan...ouch) and the C-6 transmission.
My questions are related to the regular cab truck which recently had the heads rebuilt. The previous owner stated that the valves were done and the heads were milled. From my experience working on gasoline engines, this could increase the compression slightly. Would it have an inherent bad affect on the deisel which is already at 20 to 1 or better compression? Could this have caused the engine to throw the rod? I purchased the truck with the thrown rod.
How can you tell if you have a lower end knock? My crew is very loud to begin with, let alone trying to hear a knock in the lower end.
Any help would be appreciated.
Thanks
Post Fiend
Joined: Nov 2004
Posts: 5,638
Likes: 1
From: Manitoba
There is a minimum head thickness regarding the milling of heads..... in most cases the heads are less than 5 thou over the minimum from first assy.
Minimum head thickness (from "deck" to valve cover surface): 4.7950"
If you need more let me know.
Minimum head thickness (from "deck" to valve cover surface): 4.7950"
If you need more let me know.
Thread Starter
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5th Wheeling
Joined: Dec 2007
Posts: 41
Likes: 0
From: Santa Clarita, California
PLC7.3
Thankyou for the information. I'm picking up the truck this weekend. It might be a few weeks before I can check the head thickness, but at least you have given me an idea to measure. If the heads are under the minimum...are they trash??
I did come across a 7.3 block, possibly even the whole shortblock for 200 bucks. Can 6.9 heads, intake, etc... be adapted for a 7.3? I realize the 7.3 uses larger head bolts, but can the 6.9 head holes be opened up to work? I live by the motto..... "No replacement for cubic displacement". And.... why should I build a 6.9, when I can build a 7.3 for nearly the same cost? Especially if I can use most of the 6.9 external parts on the 7.3.
Thanks again..
Thankyou for the information. I'm picking up the truck this weekend. It might be a few weeks before I can check the head thickness, but at least you have given me an idea to measure. If the heads are under the minimum...are they trash??
I did come across a 7.3 block, possibly even the whole shortblock for 200 bucks. Can 6.9 heads, intake, etc... be adapted for a 7.3? I realize the 7.3 uses larger head bolts, but can the 6.9 head holes be opened up to work? I live by the motto..... "No replacement for cubic displacement". And.... why should I build a 6.9, when I can build a 7.3 for nearly the same cost? Especially if I can use most of the 6.9 external parts on the 7.3.
Thanks again..
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
The machine shop that is doing the work on my 6.9's heads tried and failed to adapt some 6.9 heads for use on a 7.3..... something about slight differences in cooland pasages I think.
But the 6.9 block will last longer due to thicker cylinder walls.
But the 6.9 block will last longer due to thicker cylinder walls.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
86crew4me,
Welcome to FTE and the IDI diesel forum.
The bottom of the heads are flat, no combustion chamber like you would have on a gasser.
If the heads are to thin, the valves and pistons try to occupy the same space at the same time.
Not a good thing.
The clearance between the head and piston top is the thickness of the head gasket.
The 7.3 has cavitation issues that the 6.9 does not have.
You can do a minimal bore on a 6.9 to straighten out the cylinder walls, you are asking for trouble boring a 7.3 block.
Head studs are the way to go when rebuilding a 6.9.
Welcome to FTE and the IDI diesel forum.
The bottom of the heads are flat, no combustion chamber like you would have on a gasser.
If the heads are to thin, the valves and pistons try to occupy the same space at the same time.
Not a good thing.
The clearance between the head and piston top is the thickness of the head gasket.
The 7.3 has cavitation issues that the 6.9 does not have.
You can do a minimal bore on a 6.9 to straighten out the cylinder walls, you are asking for trouble boring a 7.3 block.
Head studs are the way to go when rebuilding a 6.9.
Last edited by Dave Sponaugle; Jan 8, 2008 at 08:33 PM.
Thread Starter
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5th Wheeling
Joined: Dec 2007
Posts: 41
Likes: 0
From: Santa Clarita, California
Thankyou for all the helpful replies. Hopefully I'll be able to tear the motor down in the next couple of weeks to determine tha damage and condition of the heads.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
Originally Posted by David85
The machine shop that is doing the work on my 6.9's heads tried and failed to adapt some 6.9 heads for use on a 7.3..... something about slight differences in cooland pasages I think.
But the 6.9 block will last longer due to thicker cylinder walls.
But the 6.9 block will last longer due to thicker cylinder walls.
I also will not have to rebore my 6.9, since the wear is so little, just some honing.
