Engine Mount Cap Screw with Hole Bored in Center 1

[danteeqs]

Hi, I'm new here and am hoping to find an answer to a question. I recently was replacing an expansion plug on the engine block of a 1995 Chevrolet Astro. I had to remove the upper engine mount bracket that is attached to the engine block. I noticed that the three 3/8 - 16 cap screws that attach this plate have a hole bored in the center of them. This hole goes through the the length of the cap screw from the hex head through the threaded part but not all the way through. My question is what is the purpose for this type of fastener in this application. It has me puzzled. Thanks.

 

[MikeHalloran]

I can conjecture:
- it's supposed to make the screw easier to stretch, sort of like necking the shank on the outside.
- it's used with a pin down the center, and some kind of automatic gaging device, to measure the bolt's actual stretch during installation at the factory.

... but I don't _know_.



Mike Halloran
Pembroke Pines, FL, USA

 

[TheBlacksmith]

Large (one inch plus diameter) bolts on steam turbines, etc. have a gage hole in the midddle that is used to measure stretch during tightening, so that is feasible. Torque is a very crude approximation of bolt stretch aka clamping force, so with smaller bolts and more precise designs, I could see them measuring bolt stretch as mike suggests.