Torque To Yield Head bolts. Can they be reused or not on a 3.1/3.4 L GM?

Looking for some opinions on this, especially if you do this sort of thing for a living. Here's what I have. A 1996 Century 3.1 l the oldest boy drives with water in the oil and oil in the water and 64k on the odometer. I removed the lower intake manifold only to find it's gasket in relatively good shape. The heads were next to come off and number one piston was obviously cleaner than the rest indicating a head gasket failure. The gasket didn't look visually that bad so I hauled the heads off to a local machine shop to be checked. In the meantime I went to the dealer for parts. The new head gaskets looked like a quality item but he new TTY head bolts they want to sell me are another story. They look cheap and of course they are made in Taiwan. The bolts aren't quite as long as the originals, offering less threads. Worse, one bolt is supposed to have a threaded cap on it's head for a bracket to bolt in and the replacement bolt offered had the cap but no hole or threads. I'm considering reusing the original TTY head bolts due to this obvious quality difference between originals and current over the counter. While I've found plenty of people screaming you can't reuse them, there seems to be an equally great number of people on the internet that say there is no problem, just add another 15 degrees of torque to make up for the stretch. Any help is appreciated!

 

From an engineering point of view, you cannot use them again. Everything is elastic, like an "elastic" rubberband. When you stretch it, it will return to its original state if you have not gone past the yield. Once you have yielded the bolt, the bolt is stretched. You can compensate by torquing higher, but the bolt is no longer elastic, so its not a real torque reading. Bolt design is a fairly in depth thing, and its not something i have a 100% grasp on, but there are a huge number of factors that are considered for a bolt that is engineered. I would take that knowledge over a backyard mechanic's word. But thats just me.

Will you be able to bolt it on and feel that its tight? sure. Does that mean it works? Not necessarily.

The people that are referring to bolts being reused, are probably not TTY bolts. For example, the buick 455 main bolts dont reach yield, they are over designed. Im not sure about the head bolts, but I dont think they do either. Aftermarket bolts in most cases do reach yield. They usually specify that they are TTY bolts.

Most ARP bolts also have a "stretch" measurement, and there is a tool to measure this stretch, basically to answer the question you are asking in a quantified way. But you would need to find the original specs, and that tool. The stretch is usually ~0.005" i beleive depending on the length of the bolt.


Do with that what you will.

 

not reusable....
Canadian GM pt#s are:24505015...1 stud for a/c bracket,11518953...you need 8,11518992...you need 7.

you could see if the machine shop could supply them for you.

i've worked at a GM dealer for 26 years.

 

Never replaced any on 3.1 or 3.4 engines. Never had a problem, and have done who knows how many head gaskets on those. Same for the lower intake bolts. Don't care about the theory - when the results disagree with the theory, time to change the theory. If you listen to an engineer, nothing that they design can ever fail anyway, such as the lower intake gaskets .

 

I have done several and never had one fail:TU: If you want to make a simple job difficult hire an Engineer :bla:

 

Thanks Bob,

I appreciate you guys chiming in. While I'm now pretty dang confident you can reuse these bolts at least once, I ended up buying a new set of Fel Pro bolts. They were made in USA and look to be of much better quality for half of GM's cost. I'm currently awaiting a stupid 11mm 1.5 bottoming tap before I put things back together.

 

Iron block + aluminum heads = new bolts every time. Torque to yield bolts will stretch when torqued, and very rarely spring back to original length. Go ahead and re-use the old ones, but its a gamble. It would suck to have to re-do the job cause you cheaped out on the bolts.

 

I don't think you want to use a tap; You aren't creating NEW threads, just want to clean out the old threads gunk and sealer. Try acetone in the blind holes with a wire bristle brush. Blow out with air. NAPA or Harbor Fright carries the brushes ; A battery cable cleaner brush MIGHT work. I know Summit and Jegs carry SAE thread CHASERS, but I don't know if they had metric...

 

X2...NO TAPPING. Use a thread chaser. Using a tap will remove even more parent metal which destroys the originally spec'd thread classification.

Devon

 

Go ahead and slam 'em, fellas. You don't like what engineers have to say about it, just remember that someone has to stand behind the warranty. That's why the dealer recommends replacement. If your customer sells it before the warranty on your work runs out, you both win...but someone else loses.

 

I don't worry about it anymore, Steve. I've come across so many engineering people with no hands-on understanding and so many hands-on people with no engineering understanding that as far as I'm concerned they can all enjoy their blissful ignorance and resume their daily coma.

:beer

Devon

 

Just to clarify My post earlier I would not send anything out with a customer that was unsafe or unfit. I do not wish to bash the men with the iron rings as I know You worked very hard to get were You are today but the best way to do things is not always the long and expensive way.

 

Sooooo, if the TTY bolts are so instrumental in keeping gaskets from failing, then why did the gaskets fail in the first place? When the engines were assembled at the factory, everything was new, clean, properly engineered and assembled. Gaskets still failed, and in massive pattern-failure quantities.

I also recall when GM first came out with the "updated" lower intake manifold gasket service bulletin for the 3.4L engines. The bulletin stated that the new, updated lower intake manifold bolts had to be used also. The dealers had plenty of the gaskets in stock, but GM hadn't released the bolts yet. Nice. And for you "sticklers" on GM procedure, please explain how you get a torque wrench on the lower intake manifold bolts?

Moving on to the 96-99 Buick 3800 engines. Great design putting a hot EGR pipe directly in contact with a plastic upper intake plenum. Only took "somebody" 4 years or so to figure out that that wasn't a good idea. The "fix" per the GM TSB was to replace not only melted upper intake plenum (and sometimes both the long block AND trans!!), but to replace the lower intake manifold with the "updated" one that was put into production mid year 99 . The "updated" one had an EGR pipe that was about .125" in diameter smaller than the original one. So if you followed "procedure", you would have to wack your customer another $600-$700 for the manifold, gaskets and additional labor, or you could install a smaller EGR pipe that was available in the aftermarket for about $2.

Moving on to Dexcool... boy this can go on forever.

The Trade Secret is to sometimes think outside of the box..

 

I have spent the better part of 3 decades scraping my knuckles trying to keep customers happy and providing for my family. No disrespect meant for anyone in particular, but the crap "engineering" I've seen over the years certainly doesn't mean that ALL engineers are good. By the same token, without GREAT engineers, we'd still be stuck in the Stone Age.

 

And what's wrong with Dexcool?

 

Bob, some simple questions: are you aware that engineering does not have the last word on the final product? Do you have any idea how many levels between design and delivery there are at a typical OEM, all the way down to what the dealer does to a car after receipt that can impact the product immensely?

Do you realize that there are engineers out there who can and do try hard to bridge the gaps from concept to design to prototype to testing to manufacturing to delivery to service?

Think outside the box is good advice. More good advice is to be aware that some people's boxes are bigger or smaller or the same size as others'.

If you promise not to lump all engineers as book-bound geeks, I promise not to lump all wrench turners as knuckle draggers. I am and I have been both and wouldn't change it for anything. :beers2:

Edit:

Thanks Bob, I am happy to take this as a compliment! :grin:

Just please realize that when cost estimating and manufacturing get done with some good engineering ideas, even though they presented well for assembly and service, sometimes the end result isn't so good anymore, unfortunately.

Devon

 

I always thought after looking under the hoods of the new cars that the guy that came up with that engineering Marvel must have caught a mechanic sleeping with His wifeou: Can You say REVENGE :moonu:

 

Brain, don't waste your time with the lower intake manifold gaskets that are made out of plastic. The aftermarket world like Napa has a type gasket (Fel-pro) that is made of metal and covered with rubber seals. They also have the bolts if you replace them, but I been reusing the old bolts with the metal gaskets for years with no problems. Don't forget to replace that O-ring on the oil pump drive.

 

A mechanic buddy of mine that I greatly respect said the same thing when I told him I was waiting on the tap, so I will not say you have the wrong idea by any means. But, I've done this many times before. The instructions that come with the Fel Pro bolts that I just bought said to clean the holes with a bottoming tap. I just found this in reference as well:

http://www.enginebuildermag.com/Article/84173/ten_head_bolt_installation_tips.aspx

"Run a bottoming tap down each bolt hole in the block"

If I start the tap by hand and run it down with minimal effort, how am I removing any parent metal to speak of? I'm not cutting new threads but cleaning up the ones already exisiting in the block. Funny how a debate can arise out of something unexpected.

 

Copy that...already got 'em!