omega 24 v6
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 posted on 2/8/11 at 08:06 PM |
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F***ing stretch bolts
Does anyone else hate these bloody things??
Doing a cyl head ( come to think of it all the cyl heads I've done with the angle tighten have been shite) and it's 25NM then 90 degrees
and 90 degrees and a last 90 degrees.
So did the 25Nm then the first 90 deg
Then the second 90 deg and yes you've guessed it the last bolt went crack ( well not the bolt but it pulled the threads from the block. ARGH)
And there was still 90 deg to go FFS.
Finished torque at the second 90deg works out at 75NM and there was still 90 deg to go. Now no way was that going to be acheivable without more
holes/bolts being damaged IMHO and in the past I've often stopped short of the final angle tighten because of this ( based on feel).
Bring back the old ways. Just a straight forward torque setting.
So now I'm left with a dilemma. Drill the block and tap 12mm there is some meat to do this and it does clear through the head ( coarse or
fine??) logic says fine but I have all the gear for coarse.
A 12mm allen bolt 12.9 grade would do the job I don't want to helicoil it as its 11mm*1.25 and kits are expensive for that size coupled with my
lack of faith in a helicoil for a cyl head repair.
Also trhe bolts stop 12mm short of the thread bottom in the block ???? seems a lot again IMHO.
Just pig sick ATM and needed a rant.
If it looks wrong it probably is wrong.
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MikeRJ
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| posted on 2/8/11 at 08:20 PM |
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Torque on the final 90 degrees should be little more than the previous 90 since you should be yielding the bolt at that stage. They weren't
cheap aftermarket bolts were they?
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omega 24 v6
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| posted on 2/8/11 at 08:22 PM |
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Came with the head kit mate. Decent gasket set so bolts should be as well. Just to clarify its the block thats damage not the bolt thats snapped.
If it looks wrong it probably is wrong.
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britishtrident
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| posted on 2/8/11 at 08:25 PM |
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I would hazard guess the thread that failed was in a blind hole ? If it as i suspect the hole got oil flooded and as a result hydraulic locked
when the bolt was tighted.
Following a similar but less serious incident these days I am always careful to clean and dry bolts before screwing them into blind holes.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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omega 24 v6
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| posted on 2/8/11 at 08:31 PM |
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Nope holes were clear and blown clear. A light coat of oil to threads and washer/bolt head. It was the hole where the locating dowel was and as such
there was a good 5mm less of thread to start with.
If it looks wrong it probably is wrong.
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Doctor Derek Doctors
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| posted on 2/8/11 at 08:32 PM |
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quote:
Originally posted by britishtrident
I would hazard guess the thread that failed was in a blind hole ? If it as i suspect the hole got oil flooded and as a result hydraulic locked
when the bolt was tighted.
Following a similar but less serious incident these days I am always careful to clean and dry bolts before screwing them into blind holes.
T'is likely, often the blind holes get filled with coolant when the head comes off which also causes this.
I don't know why Mr Omega is blaming the bolts when it was the head that has failed.
Designer and Supplier of the T89 Designs - Single Seater Locost. Build you own Single Seater Racecar for ~£5k.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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omega 24 v6
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| posted on 2/8/11 at 08:37 PM |
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Not blaming the bolts per se just moaning that in the good old days a torque setting was good enough no need for all this stretchy stretch crap.
And before the experts jump in with clamping forces etc etc and bolt yeild etc etc I do know/understand how it works.
Just got to figure out what to do now.
If it looks wrong it probably is wrong.
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PSpirine
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| posted on 2/8/11 at 08:43 PM |
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I must've refitted the head on my old mini A-series about 3-4 times (not due to head gasket failure) and never replaced the stock bolts (well
they were studs with nuts actually). And they always torqued up nicely - I agree with new ones being a bit more sensitive!
Mind you, the force I had to apply to undo some of the head bolts on my 2.0 DOHC boggled the mind...
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omega 24 v6
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| posted on 2/8/11 at 08:53 PM |
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Exactly what I mean PSpirine. re useable and still doing the job.
If it looks wrong it probably is wrong.
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matt_gsxr
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| posted on 2/8/11 at 08:55 PM |
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quote:
Originally posted by britishtrident
I would hazard guess the thread that failed was in a blind hole ? If it as i suspect the hole got oil flooded and as a result hydraulic locked
when the bolt was tighted.
Following a similar but less serious incident these days I am always careful to clean and dry bolts before screwing them into blind holes.
If you tighten them slowly then doesn't the oil escape and avoid these problems?
Maybe its just the old Suzuki engines, but I can easily tell when it is oil down there and just go slow.
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loggyboy
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| posted on 2/8/11 at 09:11 PM |
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Ive never had a head bolt snap on the several different types of engines ive done (VAG, renault, vauxhall 8v and 16v) to mention a few), and in fact
the final angular tightening never even seemed close to where I felt they could snap.
You mention a light coating of oil, in most of the guidance ive used it stressed to use no oil when using new bolts, and to coat only when reusing any
old bolts that were within the spec'd tolerances.
Have you checked there isnt something else in the bottom of the bolt hole (dirt, grit etc).
One thing I was suprised about is how much pressure can build up with only the slightest amount of oil in the hole.
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omega 24 v6
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| posted on 2/8/11 at 09:16 PM |
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Nothing in the hole at all block was washed out and cleaned many months ago I can assure you it was Imaculate.
Ideas on how to repair welcomed by the way.
If it looks wrong it probably is wrong.
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PSpirine
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| posted on 2/8/11 at 09:28 PM |
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What engine is it? Replacement block?
Pavs
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omega 24 v6
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| posted on 2/8/11 at 09:32 PM |
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Vauxhall c20XE there is room to drill/tap it out to m12 ( was m11 ) but that raises questions on how to maintain a torque setting as it's a
bigger dia bolt. As I was building this for a spare engine I'll prob goe this route.
No way I'll replace the block ( to expensive TBH)
If it looks wrong it probably is wrong.
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Dusty
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| posted on 2/8/11 at 09:59 PM |
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Are you sure your instructions are right. Haven't done a red top but just done my spare ST170 engine. 20Nm, 40Nm and a once and only 90 degrees.
Not three times for Henry. Seems excessive!
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craig1410
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| posted on 2/8/11 at 10:09 PM |
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Have a look at this prophetic post...
http://www.migweb.co.uk/forums/engines-transmission/239701-c20xe-anyone-know-cylinder-head-torque-settings.html
quote:
18 lbft then 3 sets of 90 degrees was revised to 18 lbft then 3 set of 60. Alot of people tend to stick with the 3 sets of 60 as cracking heads
and/or pulling the threads out the block are quite common.
http://www.sbdev.co.uk/Info_sheets/TORQUE_SETTINGS/2.0L%2016V.htm
The above link suggests graphite grease under the bolt heads and oil on the threads.
I hope you get it sorted soon.
Cheers,
Craig.
[Edited on 2/8/2011 by craig1410]
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omega 24 v6
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| posted on 2/8/11 at 10:11 PM |
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Did wonder that but going by the haynes book of lies. Anyone care to confirm that its right or wrong??
If it looks wrong it probably is wrong.
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loggyboy
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| posted on 2/8/11 at 10:50 PM |
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One of the heads i mentioned that ive done was a redtop, and would have been tightened to haynes manual specs, but would have been genuine bolts (only
£10 a set!).
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Irony
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| posted on 3/8/11 at 07:28 AM |
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I feel your pain mate. I replaced the heads on my Rover V8 not long back and one of the head bolts went 'TWANG'. My first engine, my
first head etc. I nearly had a little cry.
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MikeRJ
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| posted on 3/8/11 at 08:10 AM |
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Personaly I'd helicoil it, there shouldn't be any problems with strength. The kits are a bit expensive I agree, any chance of borrowing
one?
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atspeed racing
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| posted on 3/8/11 at 08:32 AM |
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We have done hundreds of heads and never damaged a bolt or block.
We always use EP gear oil as a lubricant for the threads and washer/bolt head.
These bolts always do up smooth and with little effort.
Do not skimp on the torque angles.
Always use new bolts.
If the bolt binds and doesnt do up smooth, remove it and re-lub and start again.
Other have a different ideas, I can only say what has worked for us in hundreds of heads with no dramas..ever.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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keithometune
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| posted on 5/8/11 at 08:39 PM |
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i always use an old head bolt with a slot hacksawed down the centre to clean the threads out first, if you can grind a path from the slot to the top
of the bolt (dremmel) this allows any liquid that may be trapped to escape. when you do the initial torque it must be spot on i have found any over
torque at this stage can make a big difference to the effort required to get the last 90 degrees.
i would use a helicoil to repair the block
keith
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britishtrident
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| posted on 5/8/11 at 09:43 PM |
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A lot of misconceptions around about stretch bolts partly because the theory of the use of steel beyond the elastic limit is very poorly taught to
engineers and technicians who as a result equate plastic deformation with failure which is not the case. The main change in the mechanical
properties of a stretch bolt that will occur after first use strain cycle of bolt is that the elastic limit of the bolt material will have
increased . The ultimate failure load of the bolt will to all intents and purposes not have changed. This first strain cylcle of the bolt is
similar to the pre-stretching process piano wire is subject to to give it superior and more stable mechanical properties.. On second and subsequent
uses of the bolt when tightened the elastic limit of the bolt will again increase but only by a tiny amount. Of course this
"ratcheting" process cannot continue indefinitely but it takes a lot cycles to reach failure, Rover for example approve reusing
bolts up to 5 times.
As for the effect on the bolts clamping force the slope gradient of the stress/strain curve beyond elastic limit doesn't change
appreciably until the materials limit of proportionality is reached.
It is ok re-use old bolts unless they have been re-used beyond the recommended number of cycles or you don't know the stress history of the
bolts.
Do not oil, instead just clean up the threads, you can even clean(nb clean not cut) the threads with a hex die (eg: non-split die ) wash with
WD40/Gas oil/Kerosene and allow to drip dry before use.
The most important stage of tightening is the first torque stage, get that wrong and the angular tighten stages will be a mile out, so it is
essential use a torque wrench which is accurate for low torques involved.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Litemoth
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| posted on 5/8/11 at 09:45 PM |
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Sounds to me like either:
* The bolts weren't to specification (i.e. they didn't yield and start stretching but transferred the full load to the internal threads
that have failed). If someone along the line has just put bolts in the kit that are the right size but not the correct material...you would have no
way of knowing until something like this happens.
OR
* The torquing procedure you have is incorrect
OR
* The threads were dodgy to start with - having said that, you can 'feel' if there's too much torque going in i recon
Lubrication (the type of lubricant that is) can have a really big effect on the torque. I tightened the head bolts up on a large press cylinder and
the specs varied by about 40% depending on the type of lubricant - Moly grease was the most effective at reducing friction i think.
it is estimated that about 90% of the torque needed to tighten an unlubricated bolt may be consumed in overcoming the underhead and the thread
friction, leaving only 10% of the actual work usefully translated into bolt tightness.
LINKY
I'd helicoil it back to the std size and get my hands on some OEM bolts...
[Edited on 5/8/11 by Litemoth]
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ss1turbo
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| posted on 5/8/11 at 10:26 PM |
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Not sure about redtops, but for other engines you can convert to studs/nuts (as used on the aforementioned A-series) - quite common for Jap stuff, I
believe - and ARP do quite a selection. You then go to a "normal" setting like the 70-90lb/ft region (sorry - not got used to these
New-tonMetres yet).
Dry/oiled/wiped is a critical factor - the "dry" setting used on a "wet" boltd/nut/stud may well exceed its strength -
especially with stretch bolts. Pulling the threads from the block does sound a bit odd - especially if its an iron block Either someone's
already been there and the threads were weakened once or its already been tapped out to M12x1.25, hence why an M11x1.25 fits? Just a thought...
Long live RWD...
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