Omega Owners Forum
Chat Area => General Car Chat => Topic started by: Doctor Gollum on 22 April 2025, 10:57:52
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Is 0.013mm a reasonable amount of distortion?
So, head is off the Nissan and whilst the block surface is true, the head is not. Basically it has this amount of distortion evenly in the centre of the head...
If you draw an oval around the middle two combustion chambers, the centre of the oval is dished into the head by this amount.
It is central both side to side and end to end.
The technical information states the following:
"Do not rework cylinder head (3) and crankcase (surface grinding).
The permissible production tolerances will otherwise be exceeded.
i Tightening the cylinder head bolts (4) compensates for a slight distortion of the cylinder head (3) in the longitudinal or transverse direction.
If cracks or unevenness are present,
↓
replace cylinder head (3) and crankcase.
Engine 282 in model 177 with transmission 700.42
AR27.10-P-0005MFD"
There are no obvious cracks and I take "unevenness" to mean rippling or twisting.
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0.013mm is about 5 tens of a thou" ..... so I'd say probably yes
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0.013mm is about 5 tens of a thou" ..... so I'd say probably yes
As in you would chance refitting it?
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0.013mm is about 5 tens of a thou" ..... so I'd say probably yes
As in you would chance refitting it?
I would ..... half a thou is pretty small :y
I'd be surprised if a skimmed head was any better ..... it definitely wouldn't be if it was done on our Bridgeport at work! ;D
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As in you would chance refitting it?
I would ..... half a thou is pretty small :y
Small enough that I wonder what was used to measure it.
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As in you would chance refitting it?
I would ..... half a thou is pretty small :y
Small enough that I wonder what was used to measure it.
I did wonder myself .... fag paper under a steel rule ..... ??? ??? ;D
I suspect that Al has his decimal point in the wrong place .... :-\ ::)
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Feeler gauge and a new steel rule of suitable length :y
I would have used a fag paper but CBA to go to the shop to get some :D
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Feeler gauge and a new steel rule of suitable length :y
I would have used a fag paper but CBA to go to the shop to get some :D
My feeler gauges don't go that small .... 1.5 thou" is the smallest IIRC (no idea in metric ???)
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You've got me thinking now :-\
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You've got me thinking now :-\
::) ::) ;D
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You've got me thinking now :-\
I think you used the imperial gauge, and wrote it as metric. 13thou warp in a head is easily measured like you did, and is enough to cause big problems.
Your next step is to get whatever machine shop you are going to use to measure it accurately, and have them advise whether it's saveable.
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You've got me thinking now :-\
::) ::) ;D
.005"
0.13mm
::)
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You've got me thinking now :-\
I think you used the imperial gauge, and wrote it as metric. 13thou warp in a head is easily measured like you did, and is enough to cause big problems.
Your next step is to get whatever machine shop you are going to use to measure it accurately, and have them advise whether it's saveable.
Precisely my next step :y
They've asked to see the head gasket too
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You've got me thinking now :-\
::) ::) ;D
.005"
0.13mm
::)
As I said then .... he's got his decimal in the wrong place. ::)
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Find out tomorrow just how knackered it actually is,. although they have reconfirmed that they can't do anything apart from clean/test it.
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Just skim it, if its measurable using standard kit then its an issue
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It can't be skimmed. The issue is that no one knows what is an acceptable amount of distortion.
As I understand it, the reason it can't be skimmed is that the head is triangular with the timing cover attached to the block, head and cam covers so any deviation has the potential to make it impossible to reassemble and seal.
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What was the main issue with it? Could having the head ringed sort it perhaps.
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It's been overheated enough to melt the baffle in the water jacket.and the head gasket popped between 2 and 3.
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Surely the cost of testing/machining would get you most of the way to a replacement head, that hasn't been cooked from the inside out :-\
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It can't be skimmed/machined!
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Surely the cost of testing/machining would get you most of the way to a replacement head, that hasn't been cooked from the inside out :-\
£80 to test it, but £2,200 for a new one.
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Can you get a second hand head from a breakers? ???
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Surely the cost of testing/machining would get you most of the way to a replacement head, that hasn't been cooked from the inside out :-\
£80 to test it, but £2,200 for a new one.
Christ! :o :o
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I 100% was not suggesting troubling Nissan, or anyone else for a brand spanking new one 👍
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It can't be skimmed. The issue is that no one knows what is an acceptable amount of distortion.
As I understand it, the reason it can't be skimmed is that the head is triangular with the timing cover attached to the block, head and cam covers so any deviation has the potential to make it impossible to reassemble and seal.
They will take quite a few thou, they won't have been made to that level of accuracy in the factory and the gaskets and sealant would take up the delta.
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Petrol, possibly '68.
Poor cold starting followed by stalling upto temperature.
Full Nissan history from new.
Recently been in to investigate and found that the thermostat casing had split. Fixed and highlighted a misfire. All plugs found to be heavily fouled and replaced and car returned only to suffer poor starting again.
I suspect that the thermostat housing contains a coolant temp sensor and as the coolant dropped it misonformed the ECU causing it to over or under fuel. Resulting in the non starting and misfiring.
Is the above a reasonable diagnosis?
Three weeks later and the thermostat housing has failed again.
Quote above copied from your original thread.
As my daughter-in-law has a 2019 petrol Qashqai I thought that I'd best look into this. It appears to be more common than it should be, so much so that the thermostat design has been changed. Some that are out of warranty but have suffered the head gasket issue as a result are trying the legal route against Nissan, stating that it must have been a known issue for Nissan to change the stat housing design.
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One source of same issues here. :y
https://www.qashqaiforums.co.uk/viewtopic.php?t=13191&start=20
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One source of same issues here. :y
https://www.qashqaiforums.co.uk/viewtopic.php?t=13191&start=20
Apparently Mercedes now fit a bracket to the housing to prevent it separating. Which is the cause of the issue, compounded by a lack of coolant level warning. Which is, er,. suboptimal given that the coolant capacity makes a K series look over filled.
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I 100% was not suggesting troubling Nissan, or anyone else for a brand spanking new one 👍
Second hand is circa £350/400 and likely to be just as buggered.
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Surely the cost of testing/machining would get you most of the way to a replacement head, that hasn't been cooked from the inside out :-\
£80 to test it, but £2,200 for a new one.
Actually they didn't charge out of pity.
The verdict:
0.18mm so basically a stupidly shaped door stop.
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7 thou" ??? I think I'd still go for the skim .... there's nothing to loose other than the cost of the skim
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It can't be skimmed. The issue is that no one knows what is an acceptable amount of distortion.
As I understand it, the reason it can't be skimmed is that the head is triangular with the timing cover attached to the block, head and cam covers so any deviation has the potential to make it impossible to reassemble and seal.
They will take quite a few thou, they won't have been made to that level of accuracy in the factory and the gaskets and sealant would take up the delta.
If you can provide the engineering drawings to confirm the factory tolerances then happy days.
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This what I meant. https://5150autosport.com/blogs/product-faq/cylinder-head-sealing-101-mls-cut-ring-o-ringing-and-fire-ringing?srsltid=AfmBOor-pnv3A4mi85Sfl_XA3Q8ZcXs0fcvG9m4bfz4ElFiMJx4UoQNQ
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Not sure how that would keep the water in. :-\
It's already an MLS gasket fwiw.
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It can't be skimmed. The issue is that no one knows what is an acceptable amount of distortion.
As I understand it, the reason it can't be skimmed is that the head is triangular with the timing cover attached to the block, head and cam covers so any deviation has the potential to make it impossible to reassemble and seal.
They will take quite a few thou, they won't have been made to that level of accuracy in the factory and the gaskets and sealant would take up the delta.
If you can provide the engineering drawings to confirm the factory tolerances then happy days.
Unlike you, I have spent enough years in engineering design to know dam well that the parts on that engine will not be machined to a tolerance that would not tolerate a fraction of a millimetre mismatch. If you were to add up the tolerance of all the mating items they will easily be closer to the 0.5mm level.
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Not sure how that would keep the water in. :-\
It's already an MLS gasket fwiw.
It would keep the water out of the combustion chambers if that was the fault
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It can't be skimmed. The issue is that no one knows what is an acceptable amount of distortion.
As I understand it, the reason it can't be skimmed is that the head is triangular with the timing cover attached to the block, head and cam covers so any deviation has the potential to make it impossible to reassemble and seal.
They will take quite a few thou, they won't have been made to that level of accuracy in the factory and the gaskets and sealant would take up the delta.
If you can provide the engineering drawings to confirm the factory tolerances then happy days.
Unlike you, I have spent enough years in engineering design to know dam well that the parts on that engine will not be machined to a tolerance that would not tolerate a fraction of a millimetre mismatch. If you were to add up the tolerance of all the mating items they will easily be closer to the 0.5mm level.
Don't let him get to you, Mark, you know what he's like. ;D
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Not sure how that would keep the water in. :-\
It's already an MLS gasket fwiw.
It would keep the water out of the combustion chambers if that was the fault
I suspect that it was more the result rather than the cause. ;)
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It can't be skimmed. The issue is that no one knows what is an acceptable amount of distortion.
As I understand it, the reason it can't be skimmed is that the head is triangular with the timing cover attached to the block, head and cam covers so any deviation has the potential to make it impossible to reassemble and seal.
They will take quite a few thou, they won't have been made to that level of accuracy in the factory and the gaskets and sealant would take up the delta.
If you can provide the engineering drawings to confirm the factory tolerances then happy days.
Unlike you, I have spent enough years in engineering design to know dam well that the parts on that engine will not be machined to a tolerance that would not tolerate a fraction of a millimetre mismatch. If you were to add up the tolerance of all the mating items they will easily be closer to the 0.5mm level.
As Mark says,any head can stand a 7 or 8 thou skim,let's be honest here,a new head basically scraps the car when added to the parts list and the new head casting is probably bare so more work/ parts being needed
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It can't be skimmed. The issue is that no one knows what is an acceptable amount of distortion.
As I understand it, the reason it can't be skimmed is that the head is triangular with the timing cover attached to the block, head and cam covers so any deviation has the potential to make it impossible to reassemble and seal.
They will take quite a few thou, they won't have been made to that level of accuracy in the factory and the gaskets and sealant would take up the delta.
If you can provide the engineering drawings to confirm the factory tolerances then happy days.
Unlike you, I have spent enough years in engineering design to know dam well that the parts on that engine will not be machined to a tolerance that would not tolerate a fraction of a millimetre mismatch. If you were to add up the tolerance of all the mating items they will easily be closer to the 0.5mm level.
Thank you for clarifying that. Unfortunately the actual tolerances are apparently a closely guarded secret, which when coupled with the fact that the official line is that the head must not be resurfaced perhaps explains why the place that tested it won't even entertain resurfacing it.
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I've lost count of the number of engine manuals I've read that say the head can't be skimmed. It's just @rse covering, surely?
I the face of F-all to lose I know what I'd do.
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I've lost count of the number of engine manuals I've read that say the head can't be skimmed. It's just @rse covering, surely?
I the face of F-all to lose I know what I'd do.
I've a 4k mile head on the way for less than the cost of skimming it, Notwithstanding that they wouldn't skim it anyway. ;)
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I've lost count of the number of engine manuals I've read that say the head can't be skimmed. It's just @rse covering, surely?
I the face of F-all to lose I know what I'd do.
I've a 4k mile head on the way for less than the cost of skimming it, Notwithstanding that they wouldn't skim it anyway. ;)
They'd do as they were fickin told if I was paying for it. Them or someone else.
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It's a moot point.
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Think I would have burned the fkg thing by now. :y
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;D
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It's a moot point.
.. as long as the 2nd hand head turns up perfectly flat. ;)
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I've lost count of the number of engine manuals I've read that say the head can't be skimmed. It's just @rse covering, surely?
I the face of F-all to lose I know what I'd do.
I agree with all of that.
Although I wonder how much arse covering is needed. A jobbing machine shop wouldn't even ask what it's off, just consider it as a chunk of metal to be made flat by removing as little material as necessary. The customer is responsible for the use it is put to, and whether that job is viable or not.
It's not that long ago that Rover insisted that their VVC mechanisms were impossible to reassemble, and any job that required it meant a new head. Back in the real world, a VVC stripped right down to the sliding blocks in the variators takes about 20minutes to build back into a working head. That's doing it with a £10 spring compressor on a Workmate in the garden...
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It's a moot point.
.. as long as the 2nd hand head turns up perfectly flat. ;)
Fine out on Wednesday.