Oh I fully planned on bottom tapping the block while installing the studs. That's why I put another thread up about needing a stud tap. I just was curious to see who hasn't and why they didn't. It is a pain having the head on the block but oh well. Life ain't always easy is it.

 

Thanks John, have you ever wondered if this was caused more by grounding the stud in the block as opposed to the threads simply pulling out due to tensional force from the head? I don't suppose there is any way to find out.

I guess the point I am coming from is that the force exerted on each thread land will not change a whole lot by having 1/2 more thread engaged. But the force exerted from thermal differential expansion between the block and the stud could be enormous if the stud was grounded. And I might think that bottom tapping just gives essentially more space between the block and the stud.

Have you noticed any thread failures after bottom tapping?

I also wonder about the failures after improper torquing post heat cycle. A loose or stretched stud is bound to fail. You have any experience on that?

I am now starting to wonder. Guess I will cross that bridge and re-do my studs if I ever go to O-Rings. Right now I can make about 55 psi of boost, but seldom go over 45 psi. I have not checked drive pressure yet.

Thanks;
Jim

 

Some of the holes in my block after being bottom tapped let me use 4-5 more threads on the stud. I dont care what fastener it is but that is a major difference not just a half turn or half thread of engagement.

To me there is really no argument here because you still have plenty of hole left so that the stud does not hit bottom. In fact I make sure none of the studs hit bottom.

Here is a picture of a set of studs where the block has been bottom tapped:
(the exhaust row studs are longer so you get some protrusion)

 

That's gotta be the 6th time I've seen that pic this week. You really like it don't ya.

 

I've been a HD Mechanic alot longer than I've been in diesel pickup performance.

 

Its a good picture I'll admit. I dont really like it or dislike it but it does get the point across.

I have found that taking pictures of just about everything I do to my trucks pays off at some point. Usually as a reference for myself or others.

 

Yeah. It's interesting though that the one I installed doesn't sit near as far down as yours do and I know it's threaded all the way. I'm hoping it's just because my buddy handed me the wrong stud. We'll see later this week.

 

I gotta add one more thing to this. DONT use shop air to clean out the threaded hole's , use a vacuum to clean , you have no idea where all those metal chips will end up.

Oh yeah , my advice is good , I stayed at the Holiday Inn Express last night

 

Well between shop air and a magnet I think I'm good. Besides, it's an all mighty cummins. It eats pieces of metal for breakfast.

 

When I bottom tapped my block it was with the head off. I used a telescoping magnet to clean out the holes.

 

Yeah. It's not fun with the head on.

 

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Good point BaldHog. My son and I do the same thing on our trucks. A vacuum will pull out all the oil, anti-freeze or any other liquid including metal and or metal chips if they are in there too.

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John_P

 

I helped a buddy put in a set of studs in his head the other day that came from haisley, and they were machined on the bottom and had no threads the last 3/8" (looked like a push rod) so with them bottom tapping would do nothing. look here

 

What year head is that?

I just went out and looked at mine again, 3 threads on the end stud and 6 on the studs over the exhaust manifold. So it looks like you would get about one more thread by bottom tapping.

Jim

 

Ahhhh those haisley studds look very nice. that machined stopped on the bottom would keep the threads happy if you put some torque on the stud. Nice.