1/2" head studs - block & cylinder deformation

[assault187]

Sure, I'd like to see some pics. Which studs were you using at 110-115 ft/lbs? That's a little high for anything 12mm.

Yes, I and most people who do this are aware of that being a high torque spec. I was using 12mm ARP L19's. My point was if people plan on using using the ARP spec of 110 lb/ft on the new stud setup, what problems may be encountered. I would think using a stronger, thicker stud would allow you to use less then recommended TQ on the fasteners (not using 110) since the studs tolerance to the pressure and resistance to streching the stud will be greater.
Once I'm out of work, I'll edit this post and upload some pics of my block and scrape a few up of cracked heads after over torque. Another thing I have noticed throughout the years, using a greater TQ spec seems distort the head stud holes in the head itself, almost pinching the studs and making the head somewhat a PITA to remove.

 

[viperlp01]

I would like to see pictures as well. I might just torque a 1/2 head stud to 110 and see if she pops. There is a lesser surface area of contact with a smaller stud compared to a larger stud to spread out the load of the threads pulling on the block. But I do agree with you on the fact that we won't have to torque these as hard. The larger stud will be able to take much more stress before it stretches.

 

[stukyl28]

Would changing the thread pitch in the block yield more gain? Meaning using a more corse thread to a more fine thread? It was just a thought I had, I have no idea if it would or not but just thought I'd share some of my left field ideas haha

 

[talonDSMerr]

But I do agree with you on the fact that we won't have to torque these as hard. The larger stud will be able to take much more clamping force before it stretches.

Fixed! All 8740 studs will stretch at the same stress. Having a bigger stud will let you apply more force before reaching that stress.

 

[viperlp01]

So does the head lift or does the stud stretch? With that being said what is the benefit if the head will still stretch regardless of head stud size? So If you take a 1" 8740 stud and say it stretches at xx, will a 1/4" 8740 stud stretch at xx.... I couldn't imagine.

 

[jrohner]

Yup. We drilled them out to accept the larger stud. Not much material removed there either.

As long as the hole that feeds oil to the head (passenger front hole) is big enough for oil to go up along side it.

 

[kthackst]

So does the head lift or does the stud stretch? With that being said what is the benefit if the head will still stretch regardless of head stud size? So If you take a 1" 8740 stud and say it stretches at xx, will a 1/4" 8740 stud stretch at xx.... I couldn't imagine.

Engineering Lesson: Stress vs Strain.

The whole idea of the head lifting/studs stretching is the same thing. The head lifts because the stud stretches. It might not stretch much but that is what happens.

The whole idea of fastener technology is to use exotic material like 8740 or L19 or pick your favorite metal and utilizing them for the stress vs strain curve. The idea is to have a material that can handle an extremely high stress with a very low strain (deformation).

The idea of going with a large stud is stress is a force over an area. So a if 8470 can handle ~200,000 psi (pounds per square inch) with a 1/2" stud you can apply a clamping force of 157080 Pounds of clamping force per stud. However a 8470 stud of 1 inch in diameter you can apply a clamping force of 628318 Pounds! The diameter of stud allow the area for the force to distribute. Think of it as a shot glass vs a scotch glass. The large diameter of the scotch glass allow it to hold more liquid.

Strain comes is to play since you want a material to have extremely low strain. As you apply stress to a bolt it stretches. The idea is to use a bolt that can take alot of stress but not stretch much at all. So when the car is under load of high cylinder pressures all the force goes into the bolt but with a low strain rate the bolt stretches but not enough to blow the headgasket. Think stock vs ARP, we know ARPs are "Stronger" but that really means they dont stretch meaning a low strain value coupled with a high tensile strength allowing more clamping force.

(This isnt directed at anyone just information out there)

 

[talonDSMerr]

^^Yup, that is good information.

Basically,

Stress = Force/Area

The yield strength (aka yield stress) of 8740 is a constant (200,000psi). Increasing the size of the stud is essentially increasing the cross sectional area. This then means you can also increase the force applied to the stud before reaching that same stress value.

It seems that the problem isn't with the head stud breaking anymore, it's whether the head/block will crack.

As for the original question, I would rehone it with a torque plate if you can. It follows the same idea as why you do a torque-plate hone while upgrading from stock to regular ARP's. Especially when you are torquing the studs to a higher value, you are now applying more clamping force, which distorts the cylinders a bit more. Knowing that, plenty have built motors without torque plates and they seem to be doing alright..

 

[viperlp01]

Ya I get it but it seemed like your were coming off as, regardless of size of the material is, the limiting factor is the type of material being used. A metal elasticity graph shows how far a certain metal can stretch before it reaches its deformation limit. With the increased stud size we can torque to a much higher clamp load before the stud reaches that stretch(deformation limit). That is one of the biggest down falls of people who think they are doing good by over torquing the hell out of there head studs. The material looses strength, its elasticity, and is no longer able to return to its original strength. It is now ruined. I am going to drill all the holes out in the project block/head and torque the head in many stages. Once I reach the point where the edges of the head crack we can now back it off say 5%

 

[donniekak]

No matter how much the studs are improved it does not fix the problem of 4 studs per cylinder. The area of the head between studs flexes and allows combustion gasses to pass, without the head actually lifting.

 

[99gst_racer]

No matter how much the studs are improved it does not fix the problem of 4 studs per cylinder. The area of the head between studs flexes and allows combustion gasses to pass, without the head actually lifting.

I agree that more studs per cylinder would be the best improvement, albiet impossible to "add" to the existing block.

But I disagree that larger studs won't benefit. A larger stud also means a larger nut and washer, which will effectivily help spread the clamping force to a wider area.

 

[99gst_racer]

I have an entire set of these studs on the way right now. John and I are going to drill and tap the rest of the holes and torque a head down to 110-115 ft lbs to see how it goes.

Also, I got word from ARP yesterday that there is no available L19 stud in this size. I'm currently awaiting a quote to have some made. Although, I'm not sure L19 is the best approach because the torque value for each stud would be around 130-135 ft/lbs, which is probably too much for the block and head to handle.

 

[BoostedBeaver]

Thanks Paul for the continued effort you continue to pour into these cars. Keep us posted with the results.

Viperlp01 a video of the tightening sequence until it pops would be entertaining, especially at your expense????

Robert

 

[BogusSVO]

well, this may be more of a "stop gap" measure....

Over bore the head bolt hole to .6250 then press fit a steel sleeve into the head bolt hole, then spot face the head bolt washer area, and mill the head gasket surface.

This way you will not "crush" the head bolt area, but still retain a good clamp on the head gasket at higer torque values.

The steel sleeve will not compressas much as the alum head, thus will force the clamp force out from the head bolt area, insted of down causing a diffrebt distortion pattern.

 

[99gst_racer]

^^^ John actually mentioned that as a possibility while we were talking yesterday.

If I were to ever go the L19 route, that's probably exactly what I'd do.

 

[ed1380]

Why would you want to increase the torque spec, when you just want to it to keep from lifting. I would think that a thicker stud doesn't need to to torqued as much because it can handle a higher force before it stretches

 

[BogusSVO]

A bolt/stud/fastner of any kind has a strech to it, you have to get it in its elastisiny range for it to have proper movement and clamp load

Too loose and the fastener will not clamp properly and alow movement.

Over tighten it, it streches too far and can not return to its desired form.

 

[99gst_racer]

Why would you want to increase the torque spec, when you just want to it to keep from lifting. I would think that a thicker stud doesn't need to to torqued as much because it can handle a higher force before it stretches

Any upgraded fastener will achieve more clamping force via a larger diameter or stronger material, both of which require a higher torque value to achieve that greater clamping force.

Basically, you'll only benefit from the updrade so long as you torque them higher.

 

[DSMReviver]

So the idea here is to avoid buying 6bolt/7bolt L19 head studs?

If you just buy the L19 it will perform just as well as this mod we are talking about?

I'm a little confused...

 

[99gst_racer]

So the idea here is to avoid buying 6bolt/7bolt L19 head studs?

If you just buy the L19 it will perform just as well as this mod we are talking about?

I'm a little confused...

The idea is that a larger diameter stud will offer a more even and wider spreading clamp load, as well as more preload (roughly 1000 lbs more) than an 11mm L19 stud, and all for a 75% lesser cost.

At this point, I'm not saying it's the greatest thing since sliced bread and that everyone should go out and do it. We're still testing and talking theory here.

 

[BoostedBeaver]

The idea is that a larger diameter stud will offer a more even and wider spreading clamp load, as well as more preload (roughly 1000 lbs more) than an 11mm L19 stud, and all for a 75% lesser cost.

At this point, I'm not saying it's the greatest thing since sliced bread and that everyone should go out and do it. We're still testing and talking theory here.

In theory, this seems to be a worthwhile mod. Distortion in the cylinder walls was my main concern, but with a minimal amount (if the graphs produced are correct) of distortion, This should be a worthwhile mod. The "cracking" issue is the next biggest worry, but with the test that viperlp01 plans to do (torquing the bolt until it does crack) should give a good basis on what can be handled by the block/head. Lastly would be the washers fitting past the valve springs. I know that my ARP washers and nuts (1990 talon) did come close to the spring itself (nut touching at one point), but you have already stated that these did clear the valve spring. I can not wait for some of these results.

Robert

 

[kthackst]

At this point, I'm not saying it's the greatest thing since sliced bread and that everyone should go out and do it.

I am going to do it...

 

[viperlp01]

I have a few junk heads at the shop.. No real expense to me .. Not one junk block though surprisingly(well actually awesome), so we had to mess with a block that was bored .020 over. I have to take care of some stuff this weekend so we might get to it, we might not. All depends if Paul wants to drive out to the shop Saturday or not.

 

[99gst_racer]

I won't have the other studs until sometime next week, so I was thinking next weekend would be better.

 

[danl]

Remember that changing stud diameter increases clamping force at the exact same torque value. Thread pitch has a slight effect on the diameter relationship between stud and nut so that will slightly effect on clamping force. If you torque to 110ft/lbs on a larger stud you will most likely run into problems. That is a large amount of clamping force. Also remember that a 6 bolt head isn't very stiff and flexes a lot when you apply a lot of clamping force to it.

You want a stud with a larger elastic stretch value before going into deformation and permanently being stretched. A larger stud can accomplish this and so can a better material. Increasing clamping force only causes problems instead of curing them.