APE studs Q. for Jay

Jay, why aren't APE studs "waisted" in the middle like stock ones? Or, to put it another way, why are the stock ones waisted?

Just curious

I'm not Jay but here's my reasoning...for what its worth.

The APE studs aren't waisted because the thicker cross section makes the studs harder to stretch in tension, which provides a more consistent clamping force. Also most guys with HD studs use the engine for drag racing where they only need oil supply for 30 seconds or so. And if top-end oiling is that critical then they use a top-end oiler.

I'm sure that the factory ones are waisted because you don't need a tremendous amount of clamping force for an engine that runs between 8.5:1-10:1 CR. The waisting also provides room for the oil to make its way to the top-end. And they save on material so they can make more for the same $$.

That's my $0.02 but I'm sure Jay has the correct answer for you.

Later, Doug

The oil in my 750 engine doesn't travel up the stud holes, there's a separate passageway for that, and even if that was the case I can't imagine an aftermarket supplier making a product that restricted the oil flow. I can't see it saving any money either, surely they are machined from rod or bar stock, the excess can't be re-used. It's been said that the radius between the thread and the waisted part (on the stockers) provides some stress relief, but the APE ones don't seem to need it.

A picture of the difference , in these studs in which you mention, would nice to see if at all possible.

The older Z1 based engines use two of the 10 cylinder stud passages to carry oil to the top-end. When using HD studs with a big block you have to check the stud passages and make sure the two oil supply ones have enough clearence or you'll starve the top end that's part of the reason for using a top-end oiling kit.

Later, Doug

You've probably already searched this, but this page suggests it's to reduce the stiffness of the bolt.
www.boltscience.com/pages/basics5.htm

Study of these diagrams provides understanding of why high performance bolts have shanks that have been reduced to a diameter below that of the outside diameter of a thread.

And this one also talks of reducing stiffness, in addition to reducing stress at the ends.
google cached search with highlighted words

Post edited by: loudhvx, at: 2007/10/21 14:25

CoreyClough wrote:

A picture of the difference , in these studs in which you mention, would nice to see if at all possible.

Can´t help you as far as the APE studs goes (because I don´t have any), but heres a pic of the studs on a KZ 650 engine - as you can see they are "waisted" or what we call "underturned" over here, the threaded parts are thicker than the rest of the stud. As Lorcan says the 650s/750s have a separate oil galley going up through the cylinder block between the outer studs, you can see the oil galley opening in the red circle.



Post edited by: OnkelB, at: 2007/10/21 15:25

Well first, our full shank studs do nor hamper oil supply to the top end. Been making the KZ stud for over 30 years and no one has ever had an oil issue.

As for the waisting... Fasteners must stretch in order to hold something together. Oem studs are not made from the same material that high performance fasteners are. If the oem stud was straight, the threads would stretch before the shank does. They undercut the center so it will stretch before the threads do.

Out studs are .5mm smaller in the shank, than the threads. They will not stretch the threads, so they do not need to be waisted any further.

Jay

Post edited by: APE Jay, at: 2007/10/21 21:24

Great answer thanks!

Thanks for the pictures and explaination Jay.