flat
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Thanks, new knowledge filed away.
So it should look like a faint cross hatch rather than glass smooth right?
Delaminated head gasket? photo's added
- Thread starter ivancrx
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So it should look like a faint cross hatch rather than glass smooth right?
new knowledge for me too!! - thanks!
what do you use to get that faint cross hatch effect? - thats what a reboring machine is for?
flat
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No idea tbh
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A rebore machine just rebores the cylinder to a new size. The cross hatch is done with an hone. And is for oil retention, cylinder lubrication purposes.
flat
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Cool thanks
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The cross hatching retains oil. This helps the rings to seal against the bore. A smooth bore allows the rings to skid on the oil film reducing the seal.
Would be interesting to know how many miles its done, i have heard of tdi doing 300k and cross hatching still being visible, feant but visible.
My 90 has 138k on the clock and the back of the clock has been opened!, still has cross hatching
My s2 tdi has done mega miles and again still has cross hatching, this also came from an off roader disco.
Neither is very fast so I doubt you are missing out on anything
My 90 has 138k on the clock and the back of the clock has been opened!, still has cross hatching
My s2 tdi has done mega miles and again still has cross hatching, this also came from an off roader disco.
Neither is very fast so I doubt you are missing out on anything
ivancrx
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Well today I have cleaned the block up checked it to ensure it is still flat, pressure tested the radiator and oil cooler and have found no problems at all with any of them. The only thing I have come up with is that either the head gasket has prematurely failed or I didn't torque it down correctly? I am going to put it all back together with a new gasket and try it again. if it fails again I know must be the block somewhere.
On a happier note I have fitted new bearings and flanges to the transfer box, and also fitted new UJ to both propshafts, just waiting on a new rear diff oil seal and it can all go back together with three less oil leaks.
On a happier note I have fitted new bearings and flanges to the transfer box, and also fitted new UJ to both propshafts, just waiting on a new rear diff oil seal and it can all go back together with three less oil leaks.
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I was wondering about your torque wrench calibration, which was why I asked how it came apart. Other than a faulty torque wrench, did you use grease on the head bolts or is there a chance that the wrong (new) bolts were used? (Apart from the fact that you should never use grease on any bolt that's going to be torqued, I wondered if grease had caused the bolts to stop hydraulically).
jamesmartin
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or how did you tighten head ?
ivancrx
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Bolts were torqued down to 30lb ft then tightened a further 60 degrees using a dial gauge, followed by a further 60 degrees tightening.
ivancrx
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Torque wrench was last calibrated about 12months ago but only used a dozen times or so since. head bolts were brand new and all the same sizes as came out originally. Now here comes the crunch bit I think, I used ARP head bolt lubricator on the bolts thinking this was the right thing to use, possibly not it may seem?
Marmaduke
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just out of interest did you properly drain the block before taking the head off to stop the threaded holes in the head filling up with coolant when you split the head? Cos that would give false readings when you try and tighten the bolts back up
If you lubricate the threads then you will overtorque the bolts by something like 30% or so. The torque that you apply is mainly used to overcome thread friction, obviously if you lubricate the thread then the friction is reduced and the bolt will therefore be at a higher loading than it would be if unlubricated. Something like 80 to 90% of the torque you apply is to overcome the thread friction, it is the remaining 20 or 10% torque that produces the actual clamping force.
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Any bolt that is torqued initially then angle tightened needs to be lightly lubricated on the threads and under the head. The pre torque tension allows for this. A very light coat of Molyslip grease on the threads and more under the head is ideal for this. Bolts should be prefitted by hand lubed up and checked for full and free entry before final assembly. Bolts that are torqued to full tension should not be lubricated. But they must be screwed into their receptor holes by hand and checked for full and free entry before being final assembled.
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ivancrx
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Block was fully drained and bolt holes blown out with compressed air.
I have just refitted the head before the rain has come and I have hand screwed the bots all in to the head (what a ball ache that was) them removed them given the holes another blow out with air then have fitted them with a tiny drop of molyslip on them and have again torqued to 30flb ft and then angle tightened them by 60 degrees twice. I just hope it works this time.
IamRobbie
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I hoovered my bores and bolt holes out with the mrs' hoover....
Err I mean the family hoover**
It then proceeded to start smoking after sucking up some water so I quickly put it away before she came home
Err I mean the family hoover**
It then proceeded to start smoking after sucking up some water so I quickly put it away before she came home
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If you don't lube them properly the initial 30 lb ft torque will not take them down far enough. It may leave them a flat or so short of where they should be before the two sixties. And then the two sixties will leave the bolts short of tension. I usually apply the initial torque leave for a time then go over them a couple of times. You would be surprised how many snug up more. Then do the angle tighten.
ivancrx
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Hmmm, would it harm them putting another 20 degrees on them?
I'd leave as-is now, you have pretty well done it as per the book anyway. Putting another 20 degrees on could potentially overstress the bolts and if it were to fail again then you wouldn't know if it was for the same reason as before or the fact that you have now used a non standard torque sequence. Many people have done it the same way in the past and not had issues.
