Are studs better than bolts?

[bcmc33]

I seem to recall as part of my education and training going back more years than I care to remember that studs are more efficient in standing applied loads in main caps and cylinder heads than bolts.

What is the modern thinking in these areas?

[lotusanglia1965]

I think once the load is applied they are much the same,however,nuts can be torqued up properly once studs are fitted to cast materials,bolts have a tendency to pull threads out...

[GrUmPyBoDgEr]

Modern thinking is "Cost effectiveness".
Whether highly loaded or not a Stud with a nut being tightened on it is the "Engineering solution"
It's much cheaper in production to screw a Bolt into a casting.
e.g. Cylinder Head covers (Valve Covers) are fixed with Bolts today but if you have to remove that cover to check valve clearances etc. the threads in the Head will quickly become destroyed. Hence Hydraulic Valve lifters & a "sealed for life" Cylinder head.
In highly loaded parts like Con-Rods it's all a bit theoretical.
Putting a Nut on a stud means that the engaged length of thread remains constant & thread friction should also be constant.
This is however can be overcome by using "Waisted" Studs that also have a constant length of thread engagement so accurate Torquing is equally possible provided the surface finish quality of the Studs can be maintained in production.
Non-waisted Bolts are however mostly used, again manufacturing costs, but it's not difficult to get the torque or more correctly the clamping load within a desired range for the application.
The surface finish/coating is a quality control problem that regularly throws automatic tightening Spindles haywire & set the alarm Bells ringing.
However the cost & technical difficulties of fitting a studs in production plus loose Washers & Nuts (that can fall anywhere & hide) rules this out in most cases.
On Cylinder heads studs are used for alignment purposes on intake & exhaust Manifold flanges.
A misaligned (cross threaded) Bolt would scrap a very expensive Cylinder head & cause major & expensive re-work.

Cheers
John

[bcmc33]

Hi John,

Thank?s for the lesson ? granny sucking eggs comes to mind, but it didn?t address my question that I thought was quite specific.

The only reason this came to my mind is that the bottom end of my engine is in pieces and I was giving serious thought to replacing head, conrod and main cap bolts as I have no idea how old they are even though the waisted head bolts are unlikely to be original. As the new ported head is likely to give me an additional 20-25% increase in power and torque, I thought discretion being the better part of valour, new fixings would be the best action.

While costing these new bolts I remembered many pieces of advice from the forum recommending ARP as being the best quality. That?s when I found that ARP do not make bolts for Twink head and main caps ? only studs. That?s when I remembered my early teaching ? hence my original statement.

And when it comes to cost, ARP is the most competative.

[GrUmPyBoDgEr]

Hi John,

Thank?s for the lesson ? granny sucking eggs comes to mind, but it didn?t address my question that I thought was quite specific.

The only reason this came to my mind is that the bottom end of my engine is in pieces and I was giving serious thought to replacing head, conrod and main cap bolts as I have no idea how old they are even though the waisted head bolts are unlikely to be original. As the new ported head is likely to give me an additional 20-25% increase in power and torque, I thought discretion being the better part of valour, new fixings would be the best action.

While costing these new bolts I remembered many pieces of advice from the forum recommending ARP as being the best quality. That?s when I found that ARP do not make bolts for Twink head and main caps ? only studs. That?s when I remembered my early teaching ? hence my original statement.

And when it comes to cost, ARP is the most competative.

Sorry that I bothered Brian,
Your question however seems to have changed & the answer is basic.
Appologies for a bit more Egg sucking:-
Any highly loaded component of unknown History must be replaced with new parts.
I'm not sure if any of the Twincam Bolts are taken into "Yield" i.e. past the "Elastic Limit" into "Plastic deformation" but if that is the case they may only be used once.
The general rule of thumb for high tensile Bolts tightened within their Elastic limit is "use up to a max. of 3 times".
ARP Bolt quality seems good, they're recommended by Engine tuners. I've used them myself but have never had the Engines in which they were used in my ownership long enough to know how they hold up.

Yes why not use ARP Studs, you'll be putting the Engine together yourself & taking your time; completely different circumstances to modern production processes. ("the modern way of thinking")
One point to consider is that if Lotus used any mechanical form of locking i.e, Tabwashers they will only stop a Bolt from turning not necessarily a Stud.

Hope now that I'm on the right Wavelength.
Cheers
John

[rocket]

My wife says she would always choose studs...

[GrUmPyBoDgEr]

My wife says she would always choose studs...

Luv it!
Thanks for bringing me back down to Earth
john

[bcmc33]

Hope now that I'm on the right Wavelength.

Not really, John,

The premise of my question was; are studs more efficient at withstanding applied loads than bolts?

It could be that this ancient belief is a load of bollox in this day and age.

I should have done this before, I know, but this is what the ARP website says in the frequently asked question section:
Do I need head bolts or studs for my engine?
This depends on the installation. On many street-driven vehicles, where the master cylinders and other items protrude into the engine compartment, it?s probably necessary to use head bolts so that the cylinder heads can be removed with the engine in the car. For most applications, however, studs are recommended. Using studs will make it much easier to assemble an engine with the cylinder head and gasket assured of proper alignment. Studs also provide more accurate and consistent torque loading.

I guess the last sentence answers my question, but I?d still like to know why. And looking at the Burton site, it appears that ARP only do studs for the Twink head and main caps.


Your mention of washers brings up a point of interest - on the engine I'm taking apart, the conrod and main cap bolts do not have washers under the heads. Ancient teaching to the fore again - I was taught that washers should always be used in such applications. The master's book (Miles Wilkins), does not show washers. But if I fit studs for the main caps there will be a need for washers, and the ARP conrod bolts come with washers. Interetsing, or what.

[paddy]

Studs also provide more accurate and consistent torque loading.

I can't back any of this up with real measurements, but..

When tightening a bolt, the torque you apply to the bolt has to overcome 2 things:

- the resistance to rotation caused by the friction of the bolt thread;
- the force needed to create the necessary level of stress in the bolt by turning it against the "ramp" of the thread.

The objective of tightening it is to achieve a specific level of stress in the bolt, but the torque applied must be greater than this by some amount depending on the level of friction.

Since a bolt is typically screwed into a material that is softer than a nut, the length of the engaged thread must be longer, and therefore the first of these forces (the friction) will be greater. This means that for a given tightening torque:

- the actual stress imparted to the bolt is lower (ie the joint is less "tight");
- the actual stress imparted is less predictable if the level of friction is not known.

To achieve a given level of stress the tightening torque will be greater, and the bolt will therefore also be closer to its torsional elastic limit (ie more likely to shear).

Paddy

[GrUmPyBoDgEr]

Hope now that I'm on the right Wavelength.

Not really, John,

The premise of my question was; are studs more efficient at withstanding applied loads than bolts?

It could be that this ancient belief is a load of bollox in this day and age.

I should have done this before, I know, but this is what the ARP website says in the frequently asked question section:
Do I need head bolts or studs for my engine?
This depends on the installation. On many street-driven vehicles, where the master cylinders and other items protrude into the engine compartment, it?s probably necessary to use head bolts so that the cylinder heads can be removed with the engine in the car. For most applications, however, studs are recommended. Using studs will make it much easier to assemble an engine with the cylinder head and gasket assured of proper alignment. Studs also provide more accurate and consistent torque loading.

I guess the last sentence answers my question, but I?d still like to know why. And looking at the Burton site, it appears that ARP only do studs for the Twink head and main caps.


Your mention of washers brings up a point of interest - on the engine I'm taking apart, the conrod and main cap bolts do not have washers under the heads. Ancient teaching to the fore again - I was taught that washers should always be used in such applications. The master's book (Miles Wilkins), does not show washers. But if I fit studs for the main caps there will be a need for washers, and the ARP conrod bolts come with washers. Interetsing, or what.

Hi Brian,

ARP should be considered as "Bolting Specialists" & I wouldn't argue the Bolt/Stud point with my limited knowledge.
If I still had my Bolt Guru's at my service I'd ask the question for you.
I know of no modern Engine that uses Studs, which as mentioned before is definitely a cost saving & certainly reduces build quality problems.
Personally I can see no advantage of tightening a Nut on to a Waisted Stud over a Waisted Bolt apart from the previously mentioned increased thread friction of the caused by the greater thread engagement of the Bolt in the Component.
I would personally prefer a bolt to a Stud in those highly loaded Joints, purely for the reason that there is only one Thread that could relax to worry about
Today it is recognised that in a highly loaded Joint, Washers should be avoided, they can cause Joint relaxation.
A Washer head Bolt (or Nut) is the accepted practice for Mains & Big End Bolts.
(Washer Head = Mating face of Nut turned to a stepped Dia. equal to or slightly less than the A/F Dim'n)
The ARP Big end Bolts that I've used in the past were so.
The ARP application you've mentioned is indeed very strange.
For Alloy Cylinder Head applications a thick larger Dia. load spreading Washer is the norm. But even here it has been observed that the surface finish of the Washer faces can seriously affect the functioning of automatic Spindles & throw up tightening "failures"


Oh & my ex-Wife preferred Studs; that's why I made a Bolt for it
All of my Stories are true but that one's truer than most

[bcmc33]

John,

The ARP studs are not waisted, but the bolts are.

ARP Head Studs.jpg (19.38 KiB) Viewed 3613 times

ARP Conrod Bolt.jpg (10.97 KiB) Viewed 3612 times

I spoke to two well known Twink engine builders today (no mames- no pack drill), and both use ARP, and I deliberately didn?t ask any silly questions like this thread.

So its ARP, then.

[miked]

Interesting stuff. I am glad I am only an Electrician.

Now heres one I have wanted to ask for a while. Re Lotus twin cam head fitting and that business of fitting two sawn off bolts and lowering the head on. The stud thing got me going!
Soory for going off subject a tad.

Am I missing something or does the cam chain slipper device (that stick out from the top of the timing chest) not baulk the head from lowering onto the two studs. I have only fitted two TWINK heads in my time, but as I see it, you can not lower onto two studs fixed in the block. I had to lift off and remove the front bolt to swing it to the left. Just used the rear which kind of messed up the whole point. Have I missed somthing really simple here. Even Miles Wilkins talks about it in his book.

Mike

[GrUmPyBoDgEr]

Out of interest, How do ARP specify their tightening procedure for:-
1. Studs (not waisted).
2. Waisted Bolts.

I anticipate for:-
1. A straightforward high Torque figure with a tolerance
2. A low torque + An Angle with tolerances

John

[JJDraper]

Couldn't quite understand your problem with the sawn off head bolts! Not sure if its different with a +2 but I have used these and it makes the job so much easier, especially when you are stretched over the engine bay and lowering the head into place. The cam chain guide is easy to flip into place as you lower the head.

Jeremy

[bcmc33]

Out of interest, How do ARP specify their tightening procedure for:-
1. Studs (not waisted).
2. Waisted Bolts.

I anticipate for:-
1. A straightforward high Torque figure with a tolerance
2. A low torque + An Angle with tolerances

John

I have asked ARP this very thing via their website.
From the information given by Burton, there is a torque value with no tolerance.

I also asked where in the yield/elastic limit range do the specified torque values get placed. I guess I could have asked the question a little better, but whether I get an answer or not is anyones guess.


John,
When did torque-angle application become popular - I guess it was the early 80's. Now that's another story - and I'm not going there.