Triangular Stainless steel high strength head bolts

Here's a batch of stainless triangular shank head bolts I just finished. I first started using these about 6 or 7 years ago after I pulled out some threads and wanted something with a little more stretch that wouldn't break things. Machining them the long way was easier for me than waisting. All the machine marks are inline with the length of the bolt and that helps avoid stress risers and breakage.

These are 180,000 tensile strength ARP bolts for Maney cylinders with american threads only.


The triangular shank bolts will replace the regular SS bolts in the photo below which snapped after years of use in a high HP 920cc alky burning motor. You can't re-torque the through bolts without taking off the head and this motor had so many races on it that I think the bolts loosened from the repeated expansion/contraction and vibration (the alum cylinders expanded/contracted but the bolts didn't). Once loose it was only a matter of time before the cylinders pounded up and down, fatigued the bolts and BOOM! - damage time.


The new bolts with fluted shanks will stretch along with the expansion/contraction/vibration of the aluminum cylinders and should stay tight. Breakage should no longer be a problem.

I've done some testing and it works just as well to cut only 2 sides on the bolts instead of 3. This saves a little time. Twin fluted bolt below. They torque down the same.



The simple jig I made for the milling process.

Hi jim, would you propose them on your site ?? thta will be nice to add them to my Maney/JS engine!!

Interesting approach, Jim. Definitely a simpler machining process. My mechanical intuition tells me that the triangular form is better than the flat strip form, but I can't come up with a reason. That wouldn't be the first time that the intuitive analysis was wrong! Just a suggestion, but you might consider sending some pics to ARP and asking their engineers what they think of this approach as opposed to the traditional reduced shank design. In my limited experience with them, they have been very helpful on design questions.

Ken

MarinAtlas - I haven't decided to market them. My products really took off this year and I would need some help before taking on more work.

Ken - I have talked to ARP about the triangular shanks and the only problem is that they are not available. I used to be able to buy them and they were made for the same purpose that waisted shanks are made. I've tested the triangular and twin flute shanks. The only advantage is that the triangular shanks still have the original diameter at the 3 corners so they locate in the bolt hole the same as a stud which means you can reduce the entire bolt shank from thread to head. Not much of an advantage but I like the looks of them and you can grab the shank with a crescent wrench when screwing in a stud. Having said all that - when it comes down to it I don't really care if they are flat fluted or round waisted like rod bolts.

This is where it all started for me years ago when I could just buy them. These also had the advantage of being forged in the triangular shank area.