KCS

iTrader: (20)

Wow, your comprehension skills are poor as well.

They can be torqued accurately, but the point is that there isn't much of a margin of safety until the fastener reaches its yield or exceeds it. You can blindly believe they're fine and reuse them, or for a whopping $50, replace them and avoid taking the unnecessary the risk that they have been compromised.

If you don't believe GM makes mistakes in manufacturing and assembling engines at the plant, you should know that there is a company by the name of Waste Management that receives faulty engines from GM for recycling by the thousands.

Randy WS6

iTrader: (69)

If you reuse the head bolt, please let use know the out come, But just remember what could happen, Broke bolt in block, blown head gasket or burn the block or heads between the chambers , for a messily 40 bucks. Ive been building these motors for years and never reused the head bolts. Its a funny thing that you can walk in any parts store and buy the head bolts, For some reason they sale them, Hum wonder why !!!!!!!

usmcz28

iTrader: (3)

You seem like the guys who would reuse a damn band aid

1quickirocz

well thats about the extent of the checking. I mean if your looking for an exact measurment well i dont go that far. We replace them as per GM advises so not alot of time is spent inspecting the bolts to figure out how much more we can twist them before they break.incase you havnt noticed your the only idiot in here telling everybody else they are wrong for replacing them. YOU must be the smartest guy in the world. way smarter then the people that design this ****.

anyways im done with this i think the OP knows what the right thing to do is based on everybody elses post. good luck with all of your stuff. hope your bolts last you forever.

joecar

To test TTY bolts, this is the procedure:
measure the length of a new bolt; toque the bolt to specification using the recommended procedure; remove the bolt and measure the length, if the bolt length is different by 0.001" or more then the bolt is now "deformed".

When a steel "bar" is stretched without going past it's yield point, it returns to its original dimension when the tension is released; when it is stretched past the yield point, it will be longer than original when the tension is removed, the bolt is now "deformed"; continual cycles past the yield point introduces fatigue (breakage of the crystal structure) which eventually (sooner or later) allows a fracture.

Below the yield point, the bolt behaves like a spring and is able to return to its original length; between zero tension and the yield point, the bolt's change of length is proportional to the tension (i.e. this is the definition of a spring); above the yield point this proportionality is lost and the bolt starts stretching at a greater rate than the increase in tension... i.e. two things happen: bolt looses ability to clamp (it is now longer) and now has fatigue cycles (as the tension on it pulls it up/down thru the yield point).

Steel has a very interesting stress-strain curve, after the yield point the stress drops as the strain increases, see these article for a brief and simplified explanation of the behaviour of steel:
http://www.feppd.org/ICB-Dent/campus...data/basic.htm
http://www.eduresourcecollection.com...Elasticity.php
There are various text books which go deeper.

I do not think GM are trying to cheat anyone... they are using the properties of a steel bolt made from a given steel alloy to achieve the maximum performance from that bolt without going to a more expensive alloy (with "higher" properties).

1quickirocz

Thank you for that. Very good info.

joecar

More links:
http://www.complore.com/properties-m...nsile-strength
http://www.tpub.com/doematerialsci/m...lscience22.htm
http://en.wikipedia.org/wiki/Deforma...engineering%29

[ Hookes law: this is how a spring behaves in it's normal operating range ]
[ stress = tensile force per unit cross sectional area of bar ]
[ strain = increase in length compared to original length of bar ]

O2Form

What i'm trying to tell you guys is these are no different than any other bolt. I'm sorry you don't see it. You are still getting all hyped on the TTY thing. don't TTY and you can reuse your bolts! If you actually TTY the bolt is no longer as strong as it was.

You guys ever hear of a company called Mercedes? they use the same head bolts and allow a percentage longer that you can measure each time untill the bolts are strechted beyond SERVICE. About 3-6 times. I'm not making this up trust me. You think ARP bolts are different than the GM bolts?

Tell ya what one of you reuse your old "factory installed bolts" and clean the threaded holes with a thread cleaner NOT A TAP and if any fail in service i will pay the repairs! I'm that sure of this.

O2Form

I'm the kinda guy that doesn't believe what others tell me unless its true.....I treat everything as suspect until proven otherwise. Do you have any idea how BS i've swallowed in 40 years in the car industry?

O'll give you a great example, I was repairing a 88 Tuned Port GTA that had a bad miss. I had this thing apart 11 times! because the techs at gm were telling me the injectors should not be bleeding off anything. I'm not talking about a dealer.. WE were the dealer. Finally i said screw this i'm testing another car that didn't miss and guess what...IT DID THE SAME DAM THING. Moral of the story is don't believe everthing you think a exprert should know.

O2Form

I just realized something, you are all assuming your head bolts are already TTY and used up. I can understand why you would then not want to use them. But they have not been UNLess you did it yourself. GM did NOT.

I don't have the exact specs to post but the bolts can be stretched quite a bit before they are not usable. Usually you would need to over heat them to get them to that point. See GM is covering their butts that no one reuses a overheated bolt. They didn't do this years ago and honestly i've seen some damage because people just don't know any better than to check ALL the bolts. Also years ago the threaded holes in the blocks were open so the bolt could be longer and not interfere, but regardless it would fail because it was too weak once heated to extremes an engine can get to.

00SSLS1

iTrader: (7)

Re use your bolts at your own risk then, I changed mine for ARP and never thought twice about it

O2Form

Chicken but smart.

Randy WS6

iTrader: (69)

I'm with him ^^^, I changed all of my Heads, rods, mains ,header bolts & harmonic balancer to ARP.

O2Form

Honestly its like when I do a pinion seal, I reuse everything but the seal and always had good results. But i've done 100's of them and know what i can get away with.

I think the most important thing when working with these aluminum blocks is to have the proper tools to clean the threaded holes. Using a tap is the WRONG thing and its risking damage. Invest in a good set of thread chasers and you wiil be so happy.

00SSLS1

iTrader: (7)

I don't like doing things twice, now that's smart

GuitsBoy

iTrader: (4)

Ive personally reused head bolts. I torqued them to ARP bolt specs since they were already stretched. It was only meant to be a temporary fix, but they made it 6K miles just fine.

disc0monkey

iTrader: (10)

02Form, your all over the place. First your saying you can reuse them because GM doesn't stretch them. Then your saying they can be stretched a lot. Then your saying if you do TTY they stretch making them weaker. I compared used bolts to new ones and they are shaped differently.

Your the type of mechanic that I pay to do a job but replaces half the **** because you "know" what your doing and I find out 2 years later you dicked me. That's why no one touches my cars but me.

disc0monkey

iTrader: (10)

how about you give some real world sources and I'll say im an idiot. you say not to trust the experts, yet you expect us to believe you against dozens of people, and you show no credentials, you don't list your qualifications, or any proof for your argument.

O2Form

I AM THE EXPERT! in my world,read between the lines of what I post and be happy!


Guitsboy I admire your ingenuity and faith in trying something others say won't work because"GM" GOD MOTORS says it won't. Those bolts will outlast you!

O2Form

Lets discuss this logicly ok? When you torque any bolt you force it to hold by twisting it until its under tension AGREED?

If we twist far enough we put it under enough tension that it is stressed and the amount of tension is equal to the strength of the bolt. If we exceed the tension point where the bolt starts to stretch farther than it can spring back to its oringinal length we just Torqued it To Yield.

Now realisicly we could do this over and over if we never exceeded yield, If we start to exceed yield every time the bolt gets a little longer every time. If we Torque to ABSOLUTE Yield the very 1st time the bolts are ONE USE ONLY.

Now heres the thing GM doesn't tell you this or how much they have been yielded or how much you can....SO BUY NEW BOLTS if you can't figure it out.

I can tell you this I watched LS1 engines being made and they were NOT TTY!