Head stud surface mods. (Totally hypothetical, don't be mad)

[miekedmr]

So, I've seen a few people building 7M heads machine out the stud hole to press in a heavy duty washer.
The idea is that having a harder landing under the head stud nut prevents the aluminum from softening/collapsing and causing a lack of tension on the head.

My question is: Is it really necessary to drill down to a greater depth, and have that thick of a washer? Would a shallower, wider washer work any worse, like the one on the right in my picture? (Assuming a nice hard + strong material, like ARP stuff or maybe a titanium washer?)

 

[hvyman]

There is not a lot of room to machine for a wide washer.

 

[suprarx7nut]

Call me dumb here, but I have never understood this practice. Here's my understanding:

1. Using the studs without any modification, you have a washer underneath the nut. The washer distributes to clamping force over the area underneath the washer as ARP designed it. This is also where Toyota felt the clamping force should be.
2. Modifying the head to accept a countersunk washer still distributes the same load from the same nut above. The difference being that the washer now has a load bearing surface further down into the head.

I'm not seeing the reduced distance between the load bearing surface and the head surface being a benefit.

What am I missing here?

 

[Piratetip]

The point of the insert is to prevent the Al head from collapsing in creating a smaller ID. --> <--
The machining & press fit of the insert makes the difference.
Another different washer on top only isn't going to prevent it.

Similarly, there is a reason Aluminum wheels use steel inserts to locate the wheel nuts...

 

[miekedmr]

Oh, cool... I didn't realize the inserts looked that way on the underside. That makes quite a bit more sense. I thought they were blocky washers like in my drawing.

 

[suprarx7nut]

The point of the insert is to prevent the Al head from collapsing in creating a smaller ID. --> <--
The machining & press fit of the insert makes the difference.
Another different washer on top only isn't going to prevent it.

Similarly, there is a reason Aluminum wheels use steel inserts to locate the wheel nuts...

View attachment 72629

Thanks for the explanation. That picture really helps. Previously I'd only seen them installed and it just looked like a countersunk collar, similar to what OP posted above. I can see how that would help keep the aluminum from collapsing and compromising the clamping force if it were press fit.

 

[Piratetip]

If a build was done on a brand new head this insert would probably not be necessary.
Since most of the heads around these days have lost a great deal of their hardness, this modification helps.
Not to mention the increased clamping load that is requested of the head now with aftermarket fasteners.

BTW this is the Part # most use for the insert:
200-8574
.5625" OD
Use appropriately sized reamer for machine work.