View Full Version : 20XE head bolt torque problem
Just bolted down my 20XE head using Haynes settings (25Nm followed by three lots of 65 degrees) and most of the bolts still feel not very tight (#2 in the tightening sequence especially). I can still tighten them further with very little force tbh. Two (one on either end) feel like they are nice and tight though
What could I have done wrong? Or what could have gone wrong?
I'm using a 1.5mm Cometic gasket, so I should be okay to re-use this if I pull all the bolts and re-do it?
comptoncj
12-06-10, 09:18 PM
Autodata says 25nm then 3 lots of 60 degrees then run the engine for 15 minutes then a further 60 degrees
mk1nova_rich
12-06-10, 09:37 PM
yes Cometic gaskets should be re-useable and as comptoncj says they need re-torquing after being run to temperature
Surely they should all feel tight, and more importantly the same, after torquing them up before running though
mk1nova_rich
12-06-10, 09:43 PM
although thinking about it, don't the Cometic gaskets specify a different torquing sequence to the standard types. Just a suggestion i may be wrong...
Here's what it says on the piece of paper I got with the gasket:
Follow manufacturers recommended torque specifications
SBD have a data sheet which specifies a series of torque settings opposed to angles specifically for Cometic gaskets, is that what you're thinking of Rich?
mk1nova_rich
12-06-10, 09:48 PM
yeh i thought that with the different compressive properties and thickness of the Cometic gaskets they would require different settings.
Yeah might try some new bolts and using SBD's torque settings. Will give them a ring on Monday and see if there's any after-engine-warmed-up torquing to do like standard.
mk1nova_rich
12-06-10, 10:00 PM
good idea pal, they should be able to point you in the right direction. hope you get it sorted :thumb:
You dont need do the "after warming" thing, that was mostly used years ago on old style headbolts i think.
Ive never further tightened mine after running the engine on any HG ive done.
You dont need do the "after warming" thing, that was mostly used years ago on old style headbolts i think.
Ive never further tightened mine after running the engine on any HG ive done.
How would you re tighten it to 25nm then 3 lots of 60 degrees without taking them off anyway? lol
Further tightening is only an additional angle MK999....
Taking the bolts out tomorrow so might as well remove the head and re-check the threads, but I think they're okay.
How would you re tighten it to 25nm then 3 lots of 60 degrees without taking them off anyway? lol
Say again? :wtf:
craig green
13-06-10, 08:55 PM
You got the proper GM bolt washers under the bolts?
There was a revised torquing value from GM later in the engines life as a reult of all the porous heads iirc. This is the figure or method to use I think & the Haynes details may well be suspect & bsed on what GM initially stated for the XE.
However I would assume SBD have got this right. Maybe its silly to assume. Get the proper information though instead of unfounded guesses on here.
You got the right bolts? iirc there's 2 types.
craig green
13-06-10, 08:58 PM
Say again? :wtf:
Think he trying to say its tricky to tighten a bolt to 25nm if its already been tightened up to a value of 25nm & had further angles added ontop of that.
Also. Any lube used on the bolt threads at all?
I used no lube as Haynes didn't say anything about it.
Early type (male) bolts with the proper washers.
I think the revised recommendation is 65 degrees, the old one being 90 degrees.
This is what I fancy using off the SBD site, which uses a series of torques opposed to angles:
CYLINDER HEAD BOLTS for Cometic gaskets
GRAPHITE GREASE UNDER HEADS & WASHERS, OIL THREADS
IF COOLING MODS HAVE BEEN DONE THEN
COMETIC GASKET MUST BE DIMPLED
STAGE 1---25 LB/FT 34NM
STAGE 2---42 LB/FT 56NM
STAGE 3---59 LB/FT 79NM
STAGE 4---75 LB/FT 100NM
Say again? :wtf:
As Craig said, didn't notice the further tightening was just an angle, seems odd to me though unless it's supposed to be tighter than 25n/3x60 degrees, in which case its not exactly going to snap the bolts doing it cold compared to warm, and if they're that close to snapping you'd be worried about running it anyway, very odd! lol
I'd try it again with a bit of lube, if the threads have anything on them at all, it won't tighten down properly as the wrench could read 25nm from a bit of grit etc.
only just dab a little oil on the threads, and then wipe most of it off. a dry thread can snag & give a false torque reading. also make sure the stud holes are clean as a whistle.
did you skim the block at all? the stud holes can have a slight burr on the top from previou torqueings, if they are pronounced (sticking up a long way) they can affect the head gaskets seating.
craig green
13-06-10, 09:18 PM
even certain oils can mess up the readings, but thats getting a bit anal.
However it can mean that a poorly prepared thread does offer resistance & the desired torque value is met earlier & less clamping pressure is applied.
As Mowgli points out, only a smear of lube, any fluid in a head bolt hole could see the side of the block pop off in extreme circumstances, hence why you should blow them out with an airline esp after a HG failure/removal. I wouldnt go mad tapping the block threads as poor technique or a 'cheap tap' could render the block needing helicoiling. Just be sure its all clean & lightly lubed with graphite grease if thats what SBD recommend for cometic's.
Just be sure its all clean & lightly lubed with graphite grease if thats what SBD recommend for cometic's.
Interestingly they say just on the heads/washers though, does kinda make sense in that greased bolts I could see coming loose, but then you come back to the issue of dry threads snagging and it starts turning into a 6 opinions each on 8 different ways kinda thing :confused:
i always use early bolts and do 25nm, 90 90 65, never had any problems apart from once, i blew headgasket, didnt skim the head and re-used the headbolts. Blew again 2 weeks later lol
Did you go round and double check the bolts were all to 25nm? middle ones loosen up slightly when you torque the outer bolts
Interestingly they say just on the heads/washers though, does kinda make sense in that greased bolts I could see coming loose, but then you come back to the issue of dry threads snagging and it starts turning into a 6 opinions each on 8 different ways kinda thing :confused:
oiling threads actually helps increase the torque on them. it is standard practise on heavy engineering. you are trying to get the underside of the bolt head to pull down tight, and the bolt needs to be wound right in to where it needs to be & then when you torque it down, it displaces any oil there is & the metal contacts properly.
on hgv wheelnuts we use 650lbft of torque to pull them up. at that sort of level, after 20 miles, the paint has been worn off the wheel rims & we retorque them on the roadside, followed by a check at the end of the day. if the threads aren't lubed, they will come undone, repeatedly, but the lubed ones stay tight. next time you hear about a lorry's wheels coming off on the radio traffic bulletin... you'll understand why
Rich I didn't go through them all to check they're all down to 25Nm, as Haynes didn't say that. As far as I was aware you torque one bolt up, then move on to the next in the sequence and you're finished with that one until the next step? I'm probably wrong tho.
The block has been skimmed at some point but not by me.
Will re-clean the bolt holes out but IIRC they were fairly clean.
craig green
13-06-10, 10:26 PM
on hgv wheelnuts we use 650lbft of torque to pull them up. at that sort of level, after 20 miles, the paint has been worn off the wheel rims & we retorque them on the roadside, followed by a check at the end of the day. if the threads aren't lubed, they will come undone, repeatedly, but the lubed ones stay tight. next time you hear about a lorry's wheels coming off on the radio traffic bulletin... you'll understand why
Yet I know a plant mechanic that says you get sacked if anyone is ever seen greasing a wheelnut. :roll:
residual grease in the threads is one thing, but adding it?
we oil the threads, not grease them. it has been standard practise in hgvs for about 50 years.. i would never grease a thread. they have vey different characteristics. we also never use a windy gun to do them up. now there are lots of people who do, but it stretches the threads on the studs & usually deforms the nuts, & gets the nuts very hot. and it always overtorques them, leading to stripping of threads, and snapped studs.
i know it sounds odd & wrong, but it is correct.
as for your mate, i think his boss must have had a wheel fall off something big.
Rang SBD and they recommended following the torquing procedure given in their info sheet, as this is specifically for a Cometic gasket.
Picked up some new bolts yesterday so will clean out the holes, check the threads and try it again.
So once I've torqued them up to the first setting, I should go back through them in order and make sure they're still torqued up right? Or is this not as important as the next torque setting will make up for it (opposed to angles which won't)
Also interestingly SBD's info sheet specifies a different tightening and removal sequence to Haynes!
iain, you are not using an OE spec gasket. and if sbd say to do it, then do it. the comeback is on them, not you
iain, you are not using an OE spec gasket. and if sbd say to do it, then do it. the comeback is on them, not younot at all as they are not bolting the head on.
if you need any more bolts i have afull set of new early ones here.
Cheers Rob, picked up a new set from Autovaux at PV which was handy.
No comeback on SBD at all, as I didn't even buy the gasket from them lol
lol, i had em in the boot fo my car. shoulda said before the weekend, yours fer a tenner.
Pulled the head off and they definitely got easier to undo towards the middle, so yeah I must have screwed up the initial 25nm torquing. Oh well :)
All the threads look fine, cleaned the holes out thoroughly ready to follow SBD's torque figures.
dont forget to grease the washers and underside of the bolt heads to sack off the friction from there.
Yeah following SBD's notes, have ordered some graphite grease to use. :)
Haynes doesn't mention anything about that tho, so I didn't know to do it for the crank sprocket bolt :(
Just torqued it down with SBD's info sheet, all the way up to 100nm.
Graphite grease under washer and head and a light oiling on the threads.
Didn't measure how many turns between each torquing but the last bolt felt like it turned way more than the others before reaching 100nm. Also one bolt felt like it moved quite a bit less than the others between the previous torquing and the last one. Does this sound alright?
Went over them a few times on the initial torque setting so they all started off the same, and been over them all again and they're all reading 100nm on my torque wrench, so should be okay?
lionel think about it logically, imagine you had three bolts in a row clamping two bits of metal together, as you do up the two outer bolts it will also pull down the middle part of the metal without doing the middle bolt. now when you go to do up the middle bolt it will be alot easier and seem you have to do it up more because it is easier. kinda hard to explain but roughly the same is happening as your doing up the head. so long as they are all done upto 100nm now you have nothing to worry about
Yeah I understand what you're saying. Yep they're all 100Nm so I'll try and forget it and not worry lol
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