special tool

Do we suspect that this is strictly to facilitate stud maintainance?

If you don't know what I am getting at, you ain't allowed on this thread..... j/k

Jon Moeller

I need to re-read a couple of sections in Smith's "Nuts, Bolts, Fasteners and Plumbing", but my initial thought is that the space eliminates shear forces on the stud. The dowels at the top of the block that slot into the head are there to locate the head on the block along the plane created by the block deck. The space between the studs and the deck of the block ensures that the only load placed on the stud is through its length.

-Jon

special tool

**** - yeah, wasn't thinking about shear.
Thanks for aiming me away from the "stupid" door.

TRP951

interesting information I was wondering the same thing

tedesco

it is also a result of the manufacturing process. If you look at the holes in the head more closely they are conical. Top diameter is bigger than bottom diameter (head gasket side). The hole are conic due to the casting process. Unfortunatly there are other conic holes in the bock as well (oil gallery) which might be part of the reason why somtimes peple get problems with rod bearings....

Laust Pedersen

It could also be space required for a deep threading tool needed to create the bottom threads (for the studs).

Porsche-O-Phile

Interesting although I seriously have to wonder if the engineers would have been worried about the shear forces through all those studs. Total # of studs x cross-sectional area = a pretty significant amount of material - MORE than enough to pick up any induced shear stresses between block & head, at least one would hope!

Hell, I've seen steel framing connections relying ONLY on shear that use smaller cross-sectional areas to transfer hundreds or thousands of pounds. I'm wondering if there's really reason to be concerned about shear here - there ain't gonna' be all that much shear acting through those studs - probably a nearly negligable amount.

I'm still trying to think of a reason they would do it conically rather than cylindrically though. . .

Laust Pedersen

Conical holes is just the natural consequence of a casting process, which needs a certain slip angle (as the coolant area has).

tedesco

preventing shere forces is not the reason for increased hole diameters in the head. Even if there was a tight fit the holes in the block are even bigger and would still allow big movements. As mentioned the holes are conical due to the casting process and because casting is not one of the most precise processes the holes are simply a bit bigger. I think to remember something like 13mm at the gasket and close to 14mm at the top of the head.

Driftomagnifico

Under the situation where you have locational head lift the bolt is placed into a shear condition as the head deflects upwards relative to the rest of the clamped section. The shear load can be transmitted by the clamped section (since it is pinned), it doesn't have to contact the stud through migration. The Fv values are obviously within tolerance of the stud material, but the repeated duration of the load could lead to a stressing of the bolt.

In normal operation what you said sounds plenty reasonable.

I typically deal with wooden structures, so I'm not 100% up to speed on steel components.

Van

I think the real reason for the diameter difference is for the proper clamping forces required for the head. When you torque down the nuts, they pull on the studs putting them in tension. This "tension" is what holds the head in place to contain the explosions of combustion. Anyhow, for the proper amount of tension, the metal has to stretch a certain amount -- so the stud has to be long enough so the steel can safely stretch without reaching it's elastic limit. Once the proper length of the studs was calculated, they knew how far down in the block to put the threads.

Now, with the knowledge that the studs would stretch, care had to be taken to ensure the "stretching" part of the studs (the middle) wouldn't contact anything. Any rubbing with the wall of the hole would throw off the desired clapming force and hold the head down unevenly (this is also why we put a little oil on the head washers and threads of the head nuts).

So, the diameter of the hole is larger than the body of the stud. And this also aids in the manufacturing of the block -- the larger counter bore would allow a tap on a long shaft to go into the hole.

Just my $0.02

JDeitz951

Zzzzzzzzzzzzzzzzzz...engineers.

tommo951

Its there to confuse you Tool!!!!!
Those guys at Ingolstadt thought it would get you in the end!!

Darwantae951

What is sheer? I'm going to become an engineer and would like to gather as much info as I can before I begin classes in a year. Thanks!

-Darwin

tommo951

Good question Darwin
Its the thickness of your girlfiends tights (pantyhose for the US boys)