Reusing TTY head bolts

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pottymouth

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I've got a 2000 Chrysler 3.2 with a bad valve. I've got pretty much everything I need to replace it and have started disassembly.

I know the rule of thumb is to replace the TTY head bolts, but have heard a few people saying that it is OK to reuse them once.

Any thoughts? I would rather not spend any more money as the car will be sold as soon as the work is completed, but I also don't want the buyer to have any problems with the head gasket.
 
Well all i can tell you is first hand i've reused head bolts a few times doing HG repairs on GM v6's and not one return.

clean the threads good use the proper torqe technique and shouldn't have a problem.
 
i think a majority of your garages replace your HG without replacing the bolts. you might wanna research and see if there is a different torque spec for reusing the same head bolts. besides cleaning those threads up well.
 
If you reuse a torque-to-yield bolt, the chance of it snapping off is far, far greater. Don't be a cheapskate, replace them.
 
Audi have a gasket tightening procedure that they say can use the bolts up to 4 times.

Looking at the stress/strain relationship of a number of bolting materials, I believe them...
 
They're just stinkin' bolts, replace them.

Some guys on the VW forum reused TTY bolts for the engine mount I believe. Every once in a while you will hear a disaster from those individuals, several months down the road. So, while it isn't a guarantee that you'll have a problem, I would feel better about buying new bolts. No point to go through all that work and have it fail due to not replacing the bolts.
 
Originally Posted By: Shannow
Audi have a gasket tightening procedure that they say can use the bolts up to 4 times.

Looking at the stress/strain relationship of a number of bolting materials, I believe them...


There is nothing wrong with reusing REGULAR head bolts. Hence the recommendation from Audi; I imagine they are NOT TTY.

However, Torque To Yield is exactly that: the bolt is torqued until it "yields". This means the fastener has been torqued to its elastic limit and will NOT return to its original length once the load has been removed from it.

That is why TTY fasteners are typically regarded as "SINGLE USE". It is NEVER a good idea to re-use them. Even if some people do.

A good article on the different types of fasteners:

http://www.enginebuildermag.com/Article/2343/threaded_fasteners_torquetoyield_and_torquetoangle.aspx
 
I had a mechanic reuse the flexplate bolts when my rear main seal was replaced. After two weeks the flexplate bolts came loose, the flexplate broke, and I was stranded. I had to tow my ole 92 mitsubishi mirage back home. I found out, he reused the old bolts and didn't use loctite. he redid the job for free.
 
TTY bolts are springs. You stretch them by a careful measured amount, and they hold parts together by spring action.
Yes, I have reused them , but it was special conditions. I won't tell you how.

Normally, DO NOT reuse them. It is very tough to retighten them to where the spring action will still work.
The normal initial torque, plus 90deg [whatever] will NOT put it back right. The used bolts are stretched.

If they are shooting at you, do what you gotta do -serious emergencies only .
I would not trust a retightened TTY bolt at all.
 
I reused the TTY bolts on my 95 Mercedes E320. These are long bolts and the shop manual gives a reuse limit on the bolt length. Mine were well within the limit.

If you understand how TTY bolts work with respect to the engineering stress-strain curve of metal, then you won't be squeamish about reusing the ones that are within reuse limits.
 
Trav, I'll have updates on my cylinder in a week or so. I'm still tearing the car down. It's taken longer than I expected, not because the work was hard, but because labor day celebrations got in the way.

Unlike most, the Mercedes manual gives specifications on how long the bolts can be prior to re-use. New is 160 mm (+-0.8 mm), but max is 162.7 mm BEFORE re-use.

I measured mine as 161, so I'll be reusing them.

I wonder if Mercedes bolts are not TTY (Torque-To-Yield), but instead TTT (Torque Turn to Tighten). Maybe these bolts are hard enough that they don't reach yield-point until 162.7 mm, and therefore are never in the plastic range?



 
As a cautious engine rebuilder in the past: I personally would cut to the chase and buy a new set of TTY bolts for your engine job.

I wouldn't take any possible risk of engine damage if the bolts are already stretched but still within limits. Afterall: once they are stretched they run a greater risk of breaking into 2 (or more pieces).

My 2c's worth. it's your money+ time and it's your engine, afterall.

Q.
 
Originally Posted By: OVERK1LL
There is nothing wrong with reusing REGULAR head bolts. Hence the recommendation from Audi; I imagine they are NOT TTY.

However, Torque To Yield is exactly that: the bolt is torqued until it "yields". This means the fastener has been torqued to its elastic limit and will NOT return to its original length once the load has been removed from it.


Nope, they are torqued beyond their elastic limit, and when the load is removed, the strain follows a path parallel to the original elastic line to a point of zero stress, which still has some permanent plastic deformation.

steel_stress_strain.gif


TTY gives good, controlled clamping forces.

As long as the total permanent strain is within the flat area, and safely within it, then multiple uses are possible. A manufacturer's material may not have enough flat area to do more than one.

If the above curve used (say) 1.5mm pitch, and 100mm effective length of the bolt, 2 tightenings would be OK, 3 touchy.

Originally Posted By: OVERK1LL
That is why TTY fasteners are typically regarded as "SINGLE USE". It is NEVER a good idea to re-use them. Even if some people do.


Like I said, it's sound engineering depending on the design employed.

I've had worse results using regular head bolts on Holdens.

I nearly always replace head bolts if they are reasonably readily available.

(Most of the bolts that I play with are covered by CEGB GOM 85, and various GE specs)
 
Originally Posted By: mechtech2
TTY bolts are springs. You stretch them by a careful measured amount, and they hold parts together by spring action.
Yes, I have reused them , but it was special conditions. I won't tell you how.

Normally, DO NOT reuse them. It is very tough to retighten them to where the spring action will still work.
The normal initial torque, plus 90deg [whatever] will NOT put it back right. The used bolts are stretched.

If they are shooting at you, do what you gotta do -serious emergencies only .
I would not trust a retightened TTY bolt at all.


Nope, regular bolts are "springs", their operation in the elastic range holds the parts together, and when undone the bolt returns to it's normal length...repeat.

TTY uses the stress/strain curve in my above post to give consistent and controlled clamping forces in a production environment.
 
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