The Top Mitsubishi Galant VR-4 Resource

Join the best E39A 1991-1992 Mitsubishi Galant VR-4 community and document your GVR4 journey.

  • Software Upgraded - Reset Your Password to Login
    In order to log in after the forum software change, you need to reset your password. If you don't have access to the email address you used to register your GVR4.org account, you won't be able to reset your password. In that case, follow the instructions here to regain access to the forum.

head studs vs bolts

paul j

Well-known member
Joined
Apr 27, 2004
Messages
282
Location
Lone Tree, CO
I have always worried that a head bolt will break and create a huge problem (pre gvr4). Much easier to get a nut off if needed over drilling a head stud. Therefore I always felt studs would make me much more comfortable. But I have never used them or broke a head bolt but when I had to use a 4ft cheater on #1551 I was certainly wondering. How many times can a bolt be re-used safely and are studs only needed for much higher than stock 10# boost compression pressure? I am speaking of gvr4 situation.
 

EHmotorsports

Well-known member
Joined
Sep 25, 2012
Messages
1,278
Location
Beaverton
Never reuse head bolts. Even if they say you can It's just cheap insurance. You can use arp head studs for stock if you want extra peace of mind. Or if you may plan to turn up the boost later.
 

mitsuturbo

Well-known member
Joined
Jun 2, 2008
Messages
3,544
Location
Near Seattle, Washington
I reused stock head bolts for YEARS and never had a problem. I've seen literally dozens of engines reuse stock head bolts with no ill effects. I've not seen one failure from a head bolt in a 6bolt engine, ever. As a matter of fact, at the dealership the bolts are checked for stretch and often reused if none is apparent. The 2g head bolts are a bit of a different story, though. We always replaced those when doing head work.

Having said that, i do concur that it is relatively cheap "insurance" to just run ARP head studs. I'm using them now, and will continue to do so in the future.
 

prove_it

Well-known member
Joined
Jul 3, 2008
Messages
4,201
Location
Sioux Falls, SD
You've never seen a bolt failure? I've seen plenty of head gasket failures on friends cars where they reused stock bolts cause they were too cheap. Then the guy turns and says "f**king dsm piece of s**t!" I roll my eyes.

Reusing head bolts is a stupid thing to do. It can work, but it's not worth the aftermath. Do it once and be done with it. Do things right and you won't have a "damn dsm" moment.
 

mitsuturbo

Well-known member
Joined
Jun 2, 2008
Messages
3,544
Location
Near Seattle, Washington
I've replaced used head bolts because they've shown some stretch, or they've felt a little "soft" when torqued, but no... i've not seen a six bolt head bolt fail yet. Maybe i just haven't known anyone dumb enough to use one that's not in good enough shape to be re-used.

The cost of ARPs is low enough that now i don't even know why i did re-use the bolts before. Probably because i was a broke-ass and couldn't afford it at the time. Oh well. I don't have to worry about it now. /ubbthreads/images/graemlins/grin.gif
 

prove_it

Well-known member
Joined
Jul 3, 2008
Messages
4,201
Location
Sioux Falls, SD
By fail do you mean break?
 

GSTwithPSI

Well-known member
Joined
Jan 1, 2012
Messages
3,460
Location
SoCal
Technically speaking, they both could be reused.

7 bolt head bolts are torque-to-yield fasteners. General practice is to use them once, and throw them away. Although, according to Mitsubishi, the 7 bolt shank is 97mm originally, and could be reused if they don't exceed 99.4mm.

6 bolt head bolts are not torque-to-yield fasteners, and are completely fine to reuse. Reusing a 6 bolt head bolt isn't stupid unless the person installing it is. Like any piece of metal, it can stretch over time and misuse. And like any bolt that isn't supposed to stretch, if the 6 bolt shank has stretched at all (originally 84mm), then don't use it. Simple. I'd bet maybe 1 out of a set of 10 would measure out of spec after being removed for the very first time. Guys have been reusing these for years without issue. For a stock rebuild, 6 bolt head bolts are more than adequate IMO.

If you want the extra assurance though, ARP studs are a good way to go, especially since the head is already off. The benefit to using studs is they are designed to take more torque than the OEM stuff. If you plan on upping the boost, a little extra clamping force on the head is never a bad thing. But don't be fooled, studs can stretch (even the mighty L19s) just like a stock head bolt, and should be measured before reuse as well.
 

moneypit

Well-known member
Joined
Jul 10, 2011
Messages
55
Location
bothell, wa
Studs are better. With bolts, all of the force is put on the head of the bolt. With studs, the force is distributed along the length of the stud not the nut.
 

GSTwithPSI

Well-known member
Joined
Jan 1, 2012
Messages
3,460
Location
SoCal
I would agree studs are better in most cases, but are you saying force is not also distributed along the length of a bolt's shank?
 
Last edited:

prove_it

Well-known member
Joined
Jul 3, 2008
Messages
4,201
Location
Sioux Falls, SD
It's a proven fact, studs are better than bolts. If it were up to engineers, all heads would be assembled with studs. Bean counters won't let them. Bolts are the cost cutting route of assembly lines.

Torque is distributed across 2 sections of thread on a stud, where on a bolt the torque is distributed across one section of thread. That is the difference. Go read all the pages of Corky Bell's "Maximum Boost" There is a section that discussed the use of bolts versus studs.

There was mention of measuring your bolts before use to verify that they are good. In a cheap build sure, the practice makes sense. I'm sure you'll find at least one bolt stretched on each head set you do. So then you buy one new one? Sure, it works. For me though I'd rather spend my time putting it together rather than measuring, cleaning and verifying all bolts torque good.

This discussion parallels with the topic of reusing MLS head gaskets. Sure, reuse them and be cheap. Don't be whining when it doesn't last though.
 

GSTwithPSI

Well-known member
Joined
Jan 1, 2012
Messages
3,460
Location
SoCal
From my understanding, it has nothing to do with force being applied to the length of the bolt/shank/stud. It has to do with how the fastener applies vertical torque to a surface.

When you thread in a bolt, it creates both twisting load as well as a vertical clamping force. As the bolt begins to accumulating a load, the bolt will both stretch and twist. Because the bolt has to react to two different forces simultaneously, its capacity to secure the head is slightly reduced.

With a nut and stud on the other hand, the nut torque provides the clamping force, rather than the torque of the entire fastener (like a bolt). A nut is torqued on a stud from a relaxed state. Unlike a bolt, pressure from the nut will make a stud stretch only along the vertical axis without a concurrent twisting load.

Simply, studs/nuts are better at applying a distributed and accurate torque load. Bolts are easier and cheaper to manufacture, hence your OEM 6 bolt hardware. At the end of the day, both will get the job done depending on application.

Quoting prove_it:
For me though I'd rather spend my time putting it together rather than measuring, cleaning and verifying all bolts torque good.



Unless you never reuse hardware and buy new every time, whether it be OEM or ARP, you still would need to measure. Hell, I've measured new ARP studs right out of the box just to make sure. 10 seconds with a dial caliper is just good insurance IMO. It's not about being cheap, it's about doing sh*t the right way.
 
Last edited:

Barnes

Well-known member
Joined
Feb 9, 2003
Messages
6,249
Location
Richland, WA
What dimension on a new ARP stud would you measure?

As for stud vs screw and strength, I'm not finding much. I'm going to keep looking.

/Mechanical Engineer
 

GSTwithPSI

Well-known member
Joined
Jan 1, 2012
Messages
3,460
Location
SoCal
Freestanding height mainly, but also any deviation in the diameter of the fastener could indicate it has been stretched. I'm no engineer, so please, correct me if i'm wrong about anything I've said here.

On a new stud, I'd look for differences in manufactured length. I wouldn't suspect them to be stretched from the factory.

An exagerated example:
attachment.php
 
Last edited:

bigblock4g63

Well-known member
Joined
Feb 10, 2009
Messages
308
Location
new jersey
Quoting mitsuturbo:
I reused stock head bolts for YEARS and never had a problem. I've seen literally dozens of engines reuse stock head bolts with no ill effects. I've not seen one failure from a head bolt in a 6bolt engine, ever. As a matter of fact, at the dealership the bolts are checked for stretch and often reused if none is apparent. The 2g head bolts are a bit of a different story, though. We always replaced those when doing head work.

Having said that, i do concur that it is relatively cheap "insurance" to just run ARP head studs. I'm using them now, and will continue to do so in the future.



at a mitsu dealer ??? dealer here never reuse the head bolts.. never reused the head bolts when I worked at porsche dealer
 

Barnes

Well-known member
Joined
Feb 9, 2003
Messages
6,249
Location
Richland, WA
On used ARP's, I could see measuring them. Preferrably you'd have the stud measure measurements when the ARP's were new so you could see any delta. But measuring would certainly show you if they were out of spec.

As for measuring ARP's that are brand new from ARP's factory, I don't see much point. I'm not sure if anyone here has had issues with their quality control. /ubbthreads/images/graemlins/dunno.gif

Also, to add to previous comments: Barring abnormal conditions, reusing OEM head screws (bolts) is perfectly acceptable. This assumes the application you will be using them for is appropriate as well.
 
Last edited:
Support Vendors who Support the GVR-4 Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications RixRacing RockAuto RTM Racing STM Tuned

Recent Forum Posts

Top