Single use head bolts vs studs

[antichrist]

I've seen, on various forums, that it's not possible to get the same clamping force in the two head bolt lengths, 66mm v 96mm, and that's one reason studs are better.
I've been curious about this claim and why Land Rover would use them if that was the case, so decided to write to a place that might know the answer, BoltScience.

This is part of the reply I received from an engineering specialist at BoltScience asking about the clamping force of a shorter vs longer bolt.

Tightening into the plastic zone, the angle of rotation is not
usually that critical (past a certain point) and so what may have been done
here is that the angle of rotation is set to ensure that the longer bolt
will be yielded, the shorter bolt will essentially sustain a bit more
plastic deformation. The preload in both cases will be similar. Essentially
once past yield, the torque-preload verses angle of rotation of the fastener
is almost horizontal.

I then replied specifying that it was a Land Rover V8 and asking about studs vs single use bolts.

Companies are increasingly going for screws instead of a stud and nut. In
this application, since the fastener is going into the plastic zone there
are a limited number of re-uses of the fastener, probably about three hence
a stud may not be such a good idea. The plus point about studs is that they
don't wear out the internal thread.

PS I've done training for Jaguar/Landrover engineers on the analysis of
bolted joints which includes tightening methods - they also use Bolt
Science's BOLTCALC program for joint analysis. I've done training courses
around the world and in my opinion, in general, they are the most
knowledgeable engineers that I've come across.

His PS was certainly interesting.

 

[Tugela]

I've done training courses around the world and in my opinion, in general, they are the most knowledgeable engineers that I've come across.

This would explain Land Rovers' impeccable reputation for reliability, head gaskets especially.

 

[aliastel]

What I like about the idea of studs is that they are less stressful on the castings, since they are not rotating and applying force at the same time. Has to be a stronger and more reliable method overall.

David

 

[p m]

I'd split the issues with head gaskets roughly halfway between the placement of cooling passages in the heads, and lack of maintenance by the owners. I don't think the head gasket issue has much to do with the choice of fasteners.

Non-TTY bolts or studs+nuts both have huge variations in clamping force. The surface of threads, presence or lack of oil/lube on threads, etc. can change it a lot. I'd think the best of both worlds could be had with studs, nuts, and crush sleeves under the nuts.

 

[listerdiesel]

The engagement length of the head bolts is more than 2 X thread diameter, and the actual 'wear' is almost nil as the rotation under load is less than a full turn.

The biggest issue with LR V8's post-dealer is the use of cr*p gaskets and often the 'wrong' gaskets.

People pick up a set of steel shim gaskets and use them on the 4.0 engine, when in fact the composite gasket is the one that should be used (Can't quickly remember if the D1 3.9 was the same)

Rubbish products and slapdash assembly are what cause the majority of head gasket failures after renewal.

Poor coolant and cooling system maintenance is another big issue.

Had one on the local forum, guy running a V8 but couldn't afford a set of new bolts.

Peter

 

[antichrist]

The engagement length of the head bolts is more than 2 X thread diameter, and the actual 'wear' is almost nil as the rotation under load is less than a full turn.

I got the feeling he was just saying in principle. Maybe even wanted to say a little something positive about studs. lol

Rubbish products and slapdash assembly are what cause the majority of head gasket failures after renewal.

That's one question I've always had and don't think I've even seen posted by anyone who's had real issues with head gasket replacement. Was their torque wrench accurate (calibrated before using) and did they use a torque-angle gauge or just guestimate at the 90 degree turns.

 

[ERover82]

The quality of bolts is another variable, and a hard one to test.

There was some doubt the bolts we use are real stretch bolts. I'd ask what he can tell from a photo of the ones we use.

Isn't one point of studs (ARP specifically) that they don't enter the plastic zone (contrary to what he said)?

 

[p m]

Was their torque wrench accurate (calibrated before using) and did they use a torque-angle gauge or just guestimate at the 90 degree turns.

I think this was addressed in your first post -

Tightening into the plastic zone, the angle of rotation is not
usually that critical (past a certain point)

 

[listerdiesel]

That's one question I've always had and don't think I've even seen posted by anyone who's had real issues with head gasket replacement. Was their torque wrench accurate (calibrated before using) and did they use a torque-angle gauge or just guestimate at the 90 degree turns.

We have three, four if you include the 3/4" drive that I used when working on trucks.

We do occasionally do a torque comparison between the 1/2" drive wrenches, they are usually pretty much within a pound or two.

If the tools are quality to start with, they stay pretty near to spec in my experience.

90 Degrees can be estimated fairly accurately, but fatigue hits the operator on the last stages! :ack:

Peter

 

[antichrist]

90 Degrees can be estimated fairly accurately, but fatigue hits the operator on the last stages! :ack:

Tell me about it! I put a 4' pipe on my breaker bar and have my wife work/watch the torque-angle gauge.

 

[singingcamel]

Gentleman, I first torque to 20 lbs,then mark the headbolts with a silver pen and do two 90 degree turns to torque.. works wll for me and takes a little guess work out of the torque process. for what its worth.

 

[pdxrovermech]

Gentleman, I first torque to 20 lbs,then mark the headbolts with a silver pen and do two 90 degree turns to torque.. works wll for me and takes a little guess work out of the torque process. for what its worth.

x2. i only use an angle gauge on a Tdi where the torque isnt an easy 90 degrees.

 

[wheelen disco]

I also use the pen method. Whether its studs or bolts its null and void when discussing a d2, it wouldn't be possible to remove the right head without first removing the studs and or the engine.

 

[antichrist]

Regarding the

Tightening into the plastic zone, the angle of rotation is not
usually that critical (past a certain point)

he may have been leading up to this

Essentially
once past yield, the torque-preload verses angle of rotation of the fastener
is almost horizontal.

It's hard for me to believe that, once beyond the threshold torque the angle of rotation doesn't matter much for clamping force variations. I think he meant the "certain point" is once past the yield point. He sent me a graph that shows a fairly steady even increase in clamping force as the degree rotation increases, until it reaches a maximum, then it levels out.

Anyway, I emailed him last night asking for clarification on it but either he was out today, or tired of me bugging him, as I haven't heard back.

I also came across this article. http://www.boltscience.com/pages/glorimertorquearticle.htm Some may find it interesting.

 

[listerdiesel]

I'd say you're right there, Tom. once you hit the stretch point the bolt isn't going to increase the clamping force any more, although it depends on 'how much' more you tighten it.

Peter

 

[roverandom]

I'm not buying it. Late Rover V8's and head gaskets are one of the most popular threads on any Land Rover forum for a reason.....and it's not just because everyone is stupid.

You would have thought that if anyone had a chance of installing the TTY bolts correctly it would be the assembly plant. But yet they fail, some managed it while being dealer serviced by the book and still under warranty. Nice.

The main reason the OEMs use TTY bolts has nothing to do with how awesome they are (or not?), it is all down to costs. Because they were able to stretch after the engine had been run in, they were supposed to be able to maintain the correct clamping force on the new composite gaskets without needing to re-torque. They also make automated engine assembly easier. Because of the stretch nature of a TTY bolt you can also get away with using a lower grade material which makes it cheaper than studs and deemed to still be able to do the job of holding the head on. Engineers at this level don't over build anything, they just try for good enough and within budget. Classic example of this is when they switched to those nasty plastic radiator fill caps.

Studs, especially high quality products such as ARP, have a proven record and are used in applications way beyond the OEM engineering mantra of "good enough and within budget". Since most folks doing head jobs are not building thousands of engines in an assembly line, studs are a viable option if you want an upgrade.

My 2c.

 

[kennith]

I'm not buying it. Late Rover V8's and head gaskets are one of the most popular threads on any Land Rover forum for a reason.....and it's not just because everyone is stupid.

A major contributor to gasket issues in these vehicles is improper cooling system maintenance, especially when combined with Dex-Cool's idiosyncrasies.

The coolant needs to be flushed every 30,000 miles or 2 years. Replacement fluids should include distilled water. Air and contaminants must be kept out of the system, both during the flush and operation. It's also good to rev the piss out of the engine every so often on nice roads.

If you do that, you'll find things work a lot more reliably.

Dex-Cool is sketchy at best in new engines with fancy alloys and composites. It's like a lithium battery. It's good until it's bad. Unlike a lithium battery, however, when that stuff goes bad, it takes everything else with it. This happens in modern engines.

Rover owners are driving around with that stuff in the most primitive engine on the road today; and they are ignoring it.

This particular engine design needed frequent coolant changes all the way back in 1962. It's like Flash Gordon's rocket-ship. In the late 1950's, someone at Buick with brill cream in their hair who didn't own a calculator once said: "Hey, I've got an idea! Let's build a V8 out of aluminum!"

It was a silly idea, but it's a silly idea that has since powered cars for half a century. That's special, because the dirty secret behind it all is the fact that the engine never really changed all that much.

If Land Rover is guilty of anything, it's pouring Dex-Cool in an engine that still rolls cigarette packs in it's shirt-sleeves, carries a switch-blade, and makes out at drive-in theaters.

To their credit, the change intervals were drastically reduced.

You've got one of the greatest engines of all time under that hood. Enjoy it. The design has it's quirks, but if feed it right, stay cool, and drive it like you stole it every now and again, you'll have a much better ownership experience.

And no. I'm not biased at all.:rofl:

Cheers,

Kennith

 

[roverandom]

Yeah, DEX-cool=NOT-cool. It has nothing to do with the engine being old as an all aluminium engine was ahead of it's time. Most modern units are all aluminium.

2 years 30,00 miles is a standard service interval for a cooling system, regardless of who makes it. Sure, it can get overlooked by some owners as a vehicle ages, just like the brake fluid....when was the last time you flushed that? But lots have failed on guy's that have performed impeccable servicing. I'm not saying that the TTY bolts don't have there place. Just saying that a high quality stud is better.

 

[ERover82]

So the lesson is, use stretch studs.

 

[antichrist]

My 2c.

The TTY head bolts aren't "lower grade" steel. Yes, not has high tensile as studs, but tensile strength isn't the only definition of steel quality.
The factory assembly tool for installing the TTY head bolts is more expensive than just a torque tool so I seriously doubt assembly costs are less. Especially when you add in that each TTY bolt has to be tightened 3 times.