OEM cylinder head bolts are not Torque to Yield (TTY), They are standard bolts

There seems to be some confusion about the oem head bolts design. Some people say they are torque to yield (TTY) bolt and hence are one time use bolts. Based on my research there is no indication the oem head bolts are TTY. My findings:


1) (My friend and Master Tech at the local Nissan dealer): ?The 300zx came out before Nissan went to TTY bolts, The FSM?s torque procedure is indicative of standard head bolts which are reusable. ?

2) The FSM makes no mention of TTY bolts

3) The FSM makes no mention of replacing the bolts and or scenarios in which they will become out of spec.

4) Most TTY bolts have a shank noticeably narrower in diameter than the threaded portion.

oem head bollt:


5) There are many people who have reused the oem head bolts without issue.

Supporting information can be found here: ASE study guide on TTY bolts versus std bolts


Other note worthy observations: I pulled up the 370Z's FSM and there is discussion about bolt stretching and runout limits


Supporting information can be found here:370Z FSM section EM



I've heard people say "Don't cheap out on your build", I understand some people will change the head bolts because people told them "it's best to do so". I think of it as the difference between a Wal-Mart Battery/tire installer versus a Nissan Master technician or engineer. The latter is preferred and even if I'm not an engineer that's the goal. Understanding what a TTY bolt is clearly shows that the VG30DE(TT) engine does not use them. Armed with this knowledge one can make an educated decision despite the status quo of using ARP or new oem head bolts.

It is my hopes this post will help people make better informed decisions and spend their money on more effective upgrades.:burnone:

 

Arp

Use many times...screw oem head bolts

 

studs for a performance engine

Studs are always better because:

-Studs are fully threaded to the bottom of the thread bore. With bolts, you're using fewer threads.

-Studs do not turn within the block threads reducing the chance of damaging them.

-With studs, there's no worry of hydraulically fracturing the block.

-With studs, the nutted end usually has fine threads making the clamping force of torquing them more accurate.


Due to the head bolt?s design,. it has both twisting force and a vertical clamping force, which means that when the cylinders within the engine?s combustion chamber begin accumulating 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 and it forms a less reliable seal in high-powered engines.

Because the stud is torqued from a relaxed state, the pressure from the nut will make it stretch only along the vertical axis without a concurrent twisting load. The result is a more evenly distributed and accurate torque load compared to that of the head bolt. This ultimately translates into higher reliability and a lower chance of head gasket failure.

Head studs are better suited for high-performance vehicles with greater power requirements, while head bolts are more practical for personal, everyday automobiles

It would be inaccurate to conclude that one type of fastener is categorically superior to the other.

At the end of the day ... DO WHAT THE F@CK YOU WANT


.

 

I might go out on a limb and play devil's advocate, but would the FSM really be written for mechanics working on the car 24 years later (after countless thousands of thermal cycles going through those bolts)?

Two scenarios come to mind:
The cheap rebuild - ie running over a cyl hone a few times, whacking on some new rings and getting out of it as cheap as possible with no allusion of reliability long-term - Use old bolts and let it be.

The big build - Having a big dollar forged motor built, and spending that extra few hundred for proper fasteners (new OEM or aftermarket), is a good way to put that extra level of security against failure which could ruin your $10K engine.

 

I can not see any problem reusing OEM head bolts for the purpose for which they were designed, stock boost.

Most people who are rebuilding will be increasing boost, the bolts and fitment specification are engineered for stock boost, they may well survive with increased boost, but when you are on a $10,000 plus build, a couple of hundred for higher spec hardware should not be an issue.

I understand where you are coming from, spending money on what is required and not on things that are not required is one of my key considerations.

But every project is different, budget, desired result, what compromises are you prepared to make to meet those goals ?

Upgraded head bolts are relatively cheap (not L19) but there failure considerably more expensive.

 

Oem head bolts

are good for 18psi without issue, which is twice stock boost, its all in who builds the engine. Screw them down out of sequence= trouble

 

what if it boost spiked to 19-20 psi

.

 

As I said beaver they may well survive increased boost but that is not what they were designed for.

Will they survive 18 PSI with a bit of pre-ignition/detonation and the increased cylinder pressures that come with that ?

We could probably run the stock pistons and rods to 25-30 PSI without a problem IF the tune was perfect and no unforseen issues occurred, that IS why we run forged pistons particularly.

 

leave the timing

standard, and the chances of pre-ignition/detonation are minimal, stupidly advancing the timing is just asking for trouble imo. If the boost spikes above pre-set, for what ever reason to 19-psi, its possible some damage may happen, but its my feeling such a small spike in pressure wont do anything, blow a gasket ect. A massive spike will fk any motor regardless of your choice of stud. There's plenty of people out there running psi on strictly stock motors with the usual bolt ons, and they don't seem to have issues. its the one's with all the goodies on a built motor and a razor tune that blow up more often than us poor slow stock freaks.

 

No one is disputing OEM bolts over studs.
Of course ARP studs are superior over OEM bolts.
For a bog standard rebuild (reconditioning) throwing away OEM bolts is wasting money when Full_Metal_Jacket has provided information that OEM bolts are not TTY bolts.

Metal fatigue on a 20yr old motor would make sense to replace with new bolts,
but if you need to replace the head gaskit after a couple of mths/yrs (for what ever reason) reusing the bolts would be ok.

It all comes down to the type of rebuild you are doing, not everyone wants to make a 600HP monster just because the engine is out.

 

After reviewing things I will concede to this; if somebody is willing to spent the money and justify forged internals they may as well do head studs too.

As for just how much of a benefit it will be to change or upgrade the cylinder head bolts in higher HP cars? That is a big gray area without empirical data.

This conversation originated from a debate about if the oem cylinder head bolts are TTY. The conversation now has shifted to if high HP cars need studs, so at least I made some progress.

 

Point

taken FMJ, but some of the above is relevant to the op's musings.

 

I dont think you are understanding the subject surrounding cylinder pressures and clamping forces, the pluses and minuses of TTY hardware, where and when they are worth using and the simple concept there is no cut and dried line when to use or not, increased material property etc are commonly used to increase capacity of a component and the head room in that specification, increasing the load on a part and removing its head room is not a great placed to be on a $10k plus engine, especially when a $200 set of hardware can maintain the parts headroom, even more especially when its an engine out and heads off failure.

By all means run your stock engine with stock hardware, but if you are doing a $10k+ rebuild and you dont use $200 worth of ARP hardware, you are an idiot.

 

Mike can you refrain from entering evidence into discussions involving popularist opinions in the future?

 

Even more so please try not to effect opinion with only half the story, otherwise crusty ol buggers with bee's in their bonnets will jump on the band wagon, but it is funny watching them fall off.

He says they "are close" to ARP's advertised numbers, close above or close below ?, I would say close below, what you need to understand also is that the advertised numbers buy ARP will probably be less then what physical tests will achieve, if the tester was serious would he not of tested an ARP item side by side ?

How about a link to Brett's original post ?

Whats funny about all this is that its over a $200 set of hardware to replace a 20 year old set for a $10,000+ engine rebuild on a high performance engine, probably aiming for a 50% plus increase in power.

As I said above there is nothing wrong with reusing stock head bolts for a stock situation, but most rebuilds tend to be aiming higher then stock performance.

This is a common problem, people are unable to see how something is applicable in one situation but not in another, for eg. what is suitable on a race car may not be on a street car, so we have people spending big money on stuff they dont need that actually performs worse on the street (say wheels/camber/suspension) for big dollars but then skimp on stuff they should have.

Maybe if head bolts/studs were shiny blue and visible they would be more popular in this discussion.

 

Tongue in cheek

about a stock engine in my car, I've spent well over ten-g on my engine and had some of the best advice going round, about what parts i should use on a 99% road going car.
Your psi comment is in part wrong, but mostly just wrong, and there is no side steeping it, you divisive old flapper.

 

What are you saying Beavs? That the tension forces put on the head bolts have everything to do with cylinder pressures and not the pressure that happens to be in the intake manifold that is in a different part of the engine???

How do you come up with this stuff??

 

In my experience the head gasket/rings/pistons/bearings are more likely to fail long before head bolts/studs fail (providing they have been installed correctly).

How many people have actually seen head bolts/studs fail under operation as opposed to other engine parts ???