ARP main studs

[bryesh]

Exactly how much difference did it make in bearing clearance, from the bolts to the studs then?

In my experiment I was using an inside mic which I seem to be able to measure to within 0.0005 (as verified by plastigauge) with some practice. As I said before using this method I really couldn't measure any difference in clearance from 70% to 120% of the recommended torque values.

All of those things you mentioned (material, thread pitch etc) are the same with the bolt as the stud, except the bolt twists in cast iron while the stud does so on the nut. Cast iron and steel have much the same friction and stiffness properties. Friction would be similar as well. The common methods of calculating bolt force from preload torque ignore the materials of the fastener and substrate altogether.

For example, this simple calculator only requires fastener diameter to calculate clamping force from applied torque. It probably uses an average friction value.
http://www.engineersedge.com/calculators/torque_calc.htm

Shigley has this simple method also, but also offers options for changing frictions conditions, etc. Friction makes a big difference but seems to be described in shigley as primarily a function of lubrication, fastener coatings etc... but it is not a function of the materials themselves.

Some of the other methods fine tune the clamping force with friction, thread pitch, finishing and others, but none that I have seen use separate calculations for studs.

All of the torque methods have one thing in common, a lot of uncertainty. Shigley has a chart that shows the scatter and it is very significant. Bolt stretch is a much better way to measure preload, but that being said, torque wrenches are universally used... so the scatter is not a bid deal in most cases. But that is why I think that clamping force would be very similar for studs and bolts, well within the scatter of the other more important factors.






As far as links go, the top reference has a link that is live, the others are books that I don't think are published on the web, they want you to pay big time.

http://www.invariantlabs.com/AIAA-2010-3022-503.pdf
http://www.amazon.com/Shigleys-Mechanical-Engineering-Design-Mcgraw-Hill/dp/0073529281
http://www.amazon.com/Airframe-Stre...d=1358388642&sr=8-6&keywords=michael+nui+book

 

[bryesh]

With the main studs are the threads different on each end?
If they are then at least one of those methods will show a difference in clamping force.

 

[fastblackracing]

With the main studs are the threads different on each end?
If they are then at least one of those methods will show a difference in clamping force.

Yes the threads are different 1/2-13 tpi on the block end and 1/2-20 tpi on the nut end. Here is how I came to find this out--- I was putting a engine together and and found that the crank would not rotate easily, this was before I checked the bearing clearance, just during the mock-up. Checked the clearance it looked wrong, but the crank pins were in spec and the bearings were the correct ones. Checking the main bores revealed that At 100 ft lbs of torque the bores were .002 under spec on the vertical dimension, so I loosened the fasteners and tightened them in 20 ft lb increments finding the bores were round and true at 40 ft lbs. As I tightened them further they became more and more out of round and undersized. So I swapped in a set of stock bolts and the measurements were slightly less off but in a similar fashion. Now this was on block that had been fitted with steel main caps and align honed. It appeared to me that the align hone had been done with the fasteners torqued to 40 ft lbs. The macine shop had no explanation for it and I ended up finding another shop That corrected the problem, I also did not see a big difference in lube I used, 30 weight oil measured about the same as arp moly lube which I found interesting. I agree scatter is prevalent and I only use a dial type torque wrench that you can watch the torque come up on and back the fastener off then retorque a time or two. Not exactly scientific but just what I found. This was 15 years ago and I did not keep all the dimensions that I found with this. Thanks for the link It will take me a while to read it through.

 

[bryesh]

Thanks for the input fastblack racing, now we're getting somewhere, that is very interesting.

What you are describing sounds like (as you said) a mistake by the machine shop. My experience is really similar to yours afterall, but my motor was machined correctly. At lower torques the clearances are off... probably before the contact surfaces have been sufficiently clamped together. If they had machined my engine at 40 ft-lbs and I had tightened it correctly, the clearance would be off similar to yours. At higher torques (in my case 70-120 ft lb which is 70-120% of the 100 ft-lb recomended), I didn't measure any change in clearances within 0.0005". You did, but you were using a bore gauge measuring 0.0001" increments.

However, the really important part of your description, you mentioned that you were getting similar (albeit bad) clearances using bolts or studs while torqing to the same values. This seems to be in line with most of the theoretical models that don't correct between bolts and studs (or different thread pitches for that matter) as well as practical experiences of some people here who have swapped bolts for studs without issues.

So in getting back to the issue of allign honing, from all of the information that is available, I think if I wanted to swap out bolts for studs I would:

1: Swap them without any additional allign honing.
2: Torque to the proper spec and check to make sure your clearances are good.
3: Enjoy some refreshing beverages and sleep well at night.

 

[carolinaturbo]

I think your right. I tourqed the house bolts checked clearly no diff. Rotation with bearings and pulled back down and bearing looked fine. Im going to try it. I will let everybody know how it holds up. Thanks