Date: Thu, 1 Dec 2016 07:46:04 -0500
Reply-To: David Bohannan <fjazzbass@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Bohannan <fjazzbass@GMAIL.COM>
Subject: Re: Over Torque Crank Bolt Damage Threads? Gas Jetta engine in
Vanagon)
In-Reply-To: <CAB2RwfgsPuJ+DvHmoKo6OXcX1UVBNBx4SLb6rUwkP1svZESFaA@mail.gmail.com>
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Isn't that the purpose of a TTY bolt? Go in once and lock in place by its own actual deformation- from Wikipedia:
A torque to yield fastener (TTY) is mounting hardware in the form of a fastener which is torqued beyond the state of elasticity and therefore undergoes plastic deformation, causing it to become permanently elongated.[1]Torquing a fastener to yield results in a high preloading of the fastener which, depending on the load frequency and amplitude, can significantly increase the fatigue life of the fastener. When the applied load doesn't surpass the clamping force of the fastener, the strain of the fastener will be lower than when the preloading is smaller than the applied load. It is therefore beneficial in high-frequency high-load situations with a higher risk of fatigue related failure, like a bolted down cylinder head, to use torque to yield bolts.
My son used TTY on his cyl heads after someone reused old TTY bolts and ended up with a head gasket leak- one time use means they warp on the way in- right??? Is it possible that the torque you applied was just doing the work of locking it in place?
I defer to the more seasoned guys....
Dave
> On Dec 1, 2016, at 1:41 AM, Neil N <musomuso@GMAIL.COM> wrote:
>
> Hi all.
>
> Sorry for asking this here but I'm leaving on a trip soon so need to
> check this detail.
>
> This is for a torque to yield bolt holding the belt drive sprocket to
> crankshaft on an ABA Jetta 2.0 gas engine in a Vanagon.
>
> I doubt the crank threads got damaged but would torquing this bolt too
> high damage (deform by pulling) the threads in crankshaft? If so, will
> the bolt work its' way out over time?
>
> The crank threads looked ok, I installed a new bolt. Since the over
> torqued bolt actually narrowed a bit about 1/2 way down the threads,
> it's likely the only thing that got damaged. The woodruff key and
> keyway look ok.
>
> Lesson: check your new torque wrench before you use it!
>
> The sprocket bolt was on REALLY tight. It took a 2' long extension on
> my breaker bar to break the bolt loose. I have an electric impact gun
> but no 12 point impact socket. To keep the crank from turning I put
> the van in gear, set the e-brake and I attempted to hold the pulley
> with a belt type pulley wrench. I used my new torque wrench for this
> job. As I kept turning the bolt, I felt no click on the wrench. Since
> the bolt was so hard to remove, I keep reefing pretty hard on this
> bolt then came to my senses. Testing the wrench on my bench, still no
> click. After zeroing the dial and resetting it to 66 ft lbs, the click
> worked.
>
> Neil.
>
>
> --
> Neil n
>
> Blog: Vanagons, Westfalia, general <http://tubaneil.blogspot.ca>
>
> 1988 Westy Images <https://picasaweb.google.com/musomuso/New1988Westy>
>
> 1981 Westfalia "Jaco" Images, technical <http://tubaneil.googlepages.com/>
>
> Vanagon-Bus VAG Gas Engine Swap Group <http://tinyurl.com/khalbay>
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