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head bolt Q


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8 replies to this topic

#1 WJM

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Posted 29 July 2005 - 06:03 PM

For EJxxx series engines...

So....are these headbolts Torque to yeild? meaning they cannot (errr...should not) be reused?

#2 Setright

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Posted 30 July 2005 - 06:07 AM

Yes sir, you must replace the bolts with brand spanking new ones!

Don't go through a HG without doing so, you'll be setting yourself up for a new HG replacement...

#3 99obw

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Posted 30 July 2005 - 08:08 AM

FWIW, I reused the bolts on our EJ25 and it's gone over 60k miles since then. With that said I am pretty sure they are torque-to-yield(kicking myself), and I don't recommend reusing them.

The new bolts we put on Pulloff's EJ22 had the heads painted, and painted heads is a signal that the bolts shouldn't be reused. I don't remember if the bolt heads on the EJ25 were painted. Traditionally head bolt heads were painted when they were retorqued the first time, so if a person tears into an engine and the head bolts are painted they shouldn't be reused.

#4 tomson1355

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Posted 30 July 2005 - 09:16 AM

I'm not sure if I understand what torque-to-yield means. If someone wants to explain it to me, I wouldn't mind.

I've twice reused head bolts on the 2.5 without problems as of 10K miles. I didn't see anything in the FSM that said not to reuse them, so I reused them.

TOm

#5 99obw

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Posted 30 July 2005 - 09:57 AM

This is my understanding based on my engineering background and car experience, FWIW.

When a material has been stressed so much that it won't return to its original dimensions, it's said to have yielded. Torque-to-yield bolts are used because the stress required to cause a given material to yield is known. If the bolts are stressed beyond the threshold of plastic deformation the resulting clamping force is consistant based on the yield strength of the material.

http://www.key-to-st...icles/Art43.htm

#6 FlyFlicker

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Posted 30 July 2005 - 10:34 AM

I'm not sure if I understand what torque-to-yield means. If someone wants to explain it to me, I wouldn't mind.

I've twice reused head bolts on the 2.5 without problems as of 10K miles. I didn't see anything in the FSM that said not to reuse them, so I reused them.

TOm


The "yeild" on a bolt means that you are stretching it beyond the point of elasticity. Once it has done this, it will never return to its original length. This presents to problems for re-using these bolts. The first is necking down of the bolt where stretching results in a narrowing of the bolt stem which results in weakness. Think of a piece of pulled taffy to picture this. The second issue is work hardening. Think of how you pull a tab off of a beer can or pop can - you repeatedly bend it back and forth until it snaps off. The repeated bending has hardened the stressed metal and made it brittle which resulted in it breaking off. The same thing happens to the bolt when you re-use it, it becomes harder and more brittle and is more prone to suffer catistrophic failure.

If you are so inclined, here is an excellent article on engine fasteners;

http://www.babcox.co.../ar/ar20134.htm

#7 Legacy777

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Posted 31 July 2005 - 02:11 PM

You can reuse the head bolts. I've talked with CCR and reputable subaru mechanics, and they don't replace the bolts.

My only question is should the torquing sequence be the same as the FSM states, or something different.

#8 NorthWet

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Posted 31 July 2005 - 02:37 PM

My reasoning on this (sitting here on my derriere and thinking) is that one way to tell if they are torque to yield is in the instructions for their torquing. If the manual/instructions say to torque to a specific setting, then they are probably not TTY. If, however, it says to torque to a specific setting, and THEN turn another 90degrees (or similar), then they are almost certainly TTY.

My only question is should the torquing sequence be the same as the FSM states, or something different.

I can't think of any good reason (see above re: reasoning ;) ) why the sequence would be any different, unless you mean doing it in x-steps to y-values. (But that is more of a procedure than a sequence.)

#9 Gnuman

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Posted 31 July 2005 - 06:50 PM

I'll throw my hat in the ring in favor of replacing the head bolts. I would take this as standard practice as well as having the heads surfaced, to insure that they are perfectly flat. While you might get away with not doing so, it is a gamble, and my heads are one thing I'd really rather not take a gamble on. which would you rather do? Take the time and money to do the job right in the first place, or have to do the job over like you should have done in the first place? I experienced this with a clutch job I did on my own car (I was in too much of a hurry to pull the flywheel and have it surfaced), and I ended up burning out the clutch prematurely, and ruining the flywheel to boot (the heat from the slipping clutch set up radial cracks in the flywheel, rendering it unusable). So the question becomes "do you want to spend a little more now, or a lot more later?" I vote for a little more now. . .




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