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Used TTY (stretch) cyl head bolts- how much do they stretch?
by
92EcoDiesel Jetta
on 04 Aug, 2011 11:33
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I measured the used 12 mm triple square cyl head bolts from my 92 EcoDiesel and they were all 115.4 mm from the shoulder to the tip of the bolt. The old bolts had these stamped markings:
BUS 10.9 Germany with what looks like a black oxide finish
The new bolts (from GermanAutoparts) looked almost identical with the same measuredlength except the stamped makings were:
W.T 10.9
Granted, these are not identical bolts from the same manufacturer and may not be a good comparison but can the stretch of the bolt be measured?
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#1
by
Mark(The Miser)UK
on 04 Aug, 2011 16:42
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I measured the used 12 mm triple square cyl head bolts from my 92 EcoDiesel and they were all 115.4 mm from the shoulder to the tip of the bolt. The old bolts had these stamped markings:
BUS 10.9 Germany with what looks like a black oxide finish
The new bolts (from GermanAutoparts) looked almost identical with the same measuredlength except the stamped makings were:
W.T 10.9
Granted, these are not identical bolts from the same manufacturer and may not be a good comparison but can the stretch of the bolt be measured?
The bolt gets stretched about a mm if my memory serves correctly.
Remember on the 12mm stuff the pocket at the bottom of the hole is about 3 turns, which makes it risky to reuse the bolts more than once for bottoming reasons if not snapping ones.
However, I have used them twice, because I only do about 45 deg turns where 90 is stipulated. I say about, because I only torque as far as it takes each time to reach level torque value.
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#2
by
theman53
on 04 Aug, 2011 19:26
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It is just different mfg. You can't usually put a name on the head of a bolt so they use a couple letter stamps.
Some will put names on not many though. I think unbrako does some. Numbers always are the grade. Those are metric grade 10.9 similar carbon content of a grade 8 SAE.
Now days the only bolt I wouldn't use inside an engine will be marked JH on the head. JH stands for Juro Hing or Jon Hing or something Hing and it is a china bolt...like most, but JH has the shadiest QC of all bolt MFG out there. Also the cheapest out there and mostly found in the hardware store Hillman fastener bins. I would bolt an alt. or water pump pulley, but never anything like a main or rod or cam cap with one.
Short reply= it will be just fine.
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#3
by
92EcoDiesel Jetta
on 04 Aug, 2011 19:51
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[
The bolt gets stretched about a mm if my memory serves correctly.
Remember on the 12mm stuff the pocket at the bottom of the hole is about 3 turns, which makes it risky to reuse the bolts more than once for bottoming reasons if not snapping ones.
However, I have used them twice, because I only do about 45 deg turns where 90 is stipulated. I say about, because I only torque as far as it takes each time to reach level torque value.[/quote]
What's "level torque value"?
I never had plans to re-use the old bolts. Just wanted to know if they actually stretch.
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#4
by
745 turbogreasel
on 04 Aug, 2011 20:44
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how much do they stretch?
Till they break
I never had plans to re-use the old bolts. Just wanted to know if they actually stretch.
Lay one thread to thread with a used one, you can see it.
]
It's a myth!
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#5
by
Mark(The Miser)UK
on 05 Aug, 2011 02:38
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[
The bolt gets stretched about a mm if my memory serves correctly.
Remember on the 12mm stuff the pocket at the bottom of the hole is about 3 turns, which makes it risky to reuse the bolts more than once for bottoming reasons if not snapping ones.
However, I have used them twice, because I only do about 45 deg turns where 90 is stipulated. I say about, because I only torque as far as it takes each time to reach level torque value.
What's "level torque value"?I never had plans to re-use the old bolts. Just wanted to know if they actually stretch.
[/quote]
Level torque value is where you are tightening, the bolt and the gauge isn't going up in value.
That is when you are (i) in the plastic range of the bolt, and (ii) in the plastic range of the gasket.
Being in the plastic range of the fibre gasket, means that polishing the head and the block, will/may lead to squirting the gasket out.
Matt surfaces better.
The late Hagar thought it good to lightly epoxy between gasket and block, leaving the head to shuffle on top...
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#6
by
Mark(The Miser)UK
on 05 Aug, 2011 02:43
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how much do they stretch?
Till they break
I never had plans to re-use the old bolts. Just wanted to know if they actually stretch.
Lay one thread to thread with a used one, you can see it.
]
It's a myth!
Are you sure?
Seeing as the bolt will only stretch in the part of the thread which is exposed, and that being whatever is left after 12 threads enter the head.
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#7
by
745 turbogreasel
on 05 Aug, 2011 02:52
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Myth = joking
You can plainly see the used ones permanently stretch about a thread.
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#8
by
Mark(The Miser)UK
on 05 Aug, 2011 05:36
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Myth = joking
You can plainly see the used ones permanently stretch about a thread.
You know how far jokes travel across the pond?
About 10ft into the sea, or knee deep; 'cuz jokes can't swim 
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#9
by
R.O.R-2.0
on 05 Aug, 2011 14:57
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they will stretch ALOT before they break.. ive never seen anyone twist one enough to break it.. my grandpa stretched one out soo bad once that one portion of threads was about twice as wide as it should have been..
instead of 11x1.25 threads, there was some 11x2.5 threads.. lol.
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#10
by
745 turbogreasel
on 05 Aug, 2011 15:05
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I had a bunch of cheap aftermarket ones break on the final 1/4 turn.
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#11
by
Mark(The Miser)UK
on 06 Aug, 2011 04:31
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I had a bunch of cheap aftermarket ones break on the final 1/4 turn.
Is that the final one after 300+ miles?
Stickshun is always a problem IMO, therefore I always use the 'old' technique of loosening each one in turn before tightening till force levels.
Some are frighteningly easy to loosen whilst others 'snap' open; yet, presumably, no gasket leak up till then
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#12
by
92EcoDiesel Jetta
on 06 Aug, 2011 06:45
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What gauge? Certainly not a click type torque wrench. Maybe a needle type or digital torque wrench with continuous readout.
Interesting about the epoxy. Anyone else try that?
About matt surface being better: So my hunch that a mirror finish on a head is not good for the same reason. You want a rougher surface to bite into the head gasket so it does not "squish out". I used 400 grit wet dry to clean the block and head surface and someone said it's too rough. 400 grit is actually too fine from the research I've done regarding cyl head finish. RA 50 is specified as a cyl head finish and that is about 130 grit. So I should have used a rougher grit than 400?
Level torque value is where you are tightening, the bolt and the gauge isn't going up in value.
That is when you are (i) in the plastic range of the bolt, and (ii) in the plastic range of the gasket.
Being in the plastic range of the fibre gasket, means that polishing the head and the block, will/may lead to squirting the gasket out.
Matt surfaces better.
The late Hagar thought it good to lightly epoxy between gasket and block, leaving the head to shuffle on top...[/quote]
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#13
by
92EcoDiesel Jetta
on 06 Aug, 2011 07:40
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I just placed a new head bolt, thread to thread, against a used head bolt. The threads meshed perfectly in the portion that was threaded inside the block. Outside, they did not mesh perfectly but very close. A new bolt against a new bolt meshed perfectly the entire length of the threads. This shows the used bolt did stretch a teeny amount that's difficult to measure (lengthwise with a vernier caliper).,
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#14
by
Mark(The Miser)UK
on 06 Aug, 2011 14:03
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If it was me re the "400 grit being too rough", it was more in reference to cleaning stubborn crud off with a rotary tool.
With a clean set of faces then roughing with a flat block is how I'd do it.
People who don't hand skim and send away get milling ridges on it.
Some machinists then say they need to remove the inconel precups