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#15
by
wil892
on 13 Sep, 2011 12:54
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Ok, I had a chance to compare this head with my old head (which is genuine). It looks like the exhaust valves are a lot closer to the cylinder head face than my old genuine head. They really are almost level with the face of the head whereas the old genuine head has its exhaust valves sunken further into the head with a greater distance between the face.
I think i'm going to take the head to where I got it to have it checked out and just see what they say about it. I have no technical experience with cylinder head building so not really in the best of positions to point the finger.
While the head has worked, I think i'm going to try and find a decent genuine one that I can get built up, as this has kind of shown me why these "chinese" cylinder heads haven't the best name.
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#16
by
wil892
on 23 Sep, 2011 11:43
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Ok, spoke to the place who originally built the head. They are very helpful but are blaming it on incorrect timing, which is fair enough as it must happen quite a lot.
HOWEVER, I know for a fact this engine has always had correct timing, so I believe the head is still to blame.
Is there a minimum valve recession spec that is required in these engines? Doing a search I have found there is obviously a maximum, but no minimum.
Basically the exhaust valves are showing next to no recession from the cylinder head surface, while the inlets show visible recession as on my old head.
There is no camshaft installed so all valves are fully seated.
I have not had the chance to measure the recession but I'm not joking, the exhaust valves can practically be seen if i look at the head surface horizontally, which just doesnt seem right.
If I can sort out some information and measure the recessions I will get in touch with the shop again to see what they say.
Would this minimal amount of recession lead to valve piston contact at higher rpm?
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#17
by
rodpaslow
on 23 Sep, 2011 11:53
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The valves are recessed some as you suggest. I do remember reading somewhere that if machining of the head surface is needed, a max of .005" can be taken off. So the valves will still be recessed. Can you measure the depth of recess and see if a 3 notch mls gasket will make up the difference? If the head has been working fine otherwise can you makeup the difference with a thicker head gasket? If not a vw head is the only option...$.02
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#18
by
RabbitJockey
on 23 Sep, 2011 11:53
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sounds like they shaved it too much.
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#19
by
745 turbogreasel
on 23 Sep, 2011 12:52
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The valves are recessed some as you suggest. I do remember reading somewhere that if machining of the head surface is needed, a max of .005" can be taken off. So the valves will still be recessed. Can you measure the depth of recess and see if a 3 notch mls gasket will make up the difference? If the head has been working fine otherwise can you makeup the difference with a thicker head gasket? If not a vw head is the only option...$.02
Measure yours against specification.
IME thicker gasket just doesn't run the same.
You can get the seats and or valves cut down on any head.
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#20
by
RabbitJockey
on 23 Sep, 2011 17:16
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The valves are recessed some as you suggest. I do remember reading somewhere that if machining of the head surface is needed, a max of .005" can be taken off. So the valves will still be recessed. Can you measure the depth of recess and see if a 3 notch mls gasket will make up the difference? If the head has been working fine otherwise can you makeup the difference with a thicker head gasket? If not a vw head is the only option...$.02
Measure yours against specification.
IME thicker gasket just doesn't run the same.
You can get the seats and or valves cut down on any head.
that is the best solution, shouldn't cost much either, well a new head is the best option.
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#21
by
rabbitman
on 23 Sep, 2011 22:13
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From the bentley: surface of head to valve face, Maximum = 1.5mm and minimum = .5mm.
Sounds like they have to redo it. Everyone knows that on these engines the valves get close to the pistons all the time, having the valves start out even closer is a really good way to make it interfere during operation.
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#22
by
RabbitJockey
on 23 Sep, 2011 22:59
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i guess they shaved the head even tho it was brand new? a lot of machine shops will skim every head that comes in, which is fine on gas engines where they just straighten them up to make sure the customer doesn't come back to them, but on these engines, it really should only be done out of necessity, i had an excellent condition used head, it doesn't even have cracks between the valves, i didn't tell the machine shop i had rebuild it not to shave they head, and they did, this head was so straight it was crazy... ugh i know for next time tho to tell them not to.
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#23
by
745 turbogreasel
on 24 Sep, 2011 05:13
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i guess they shaved the head even tho it was brand new?
I'd not be surprised if ChinaHead didn't put the seats at the right depth to start, or got a batch of thicker valves.
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#24
by
Mark(The Miser)UK
on 24 Sep, 2011 13:19
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From the bentley: surface of head to valve face, Maximum = 1.5mm and minimum = .5mm.Sounds like they have to redo it. Everyone knows that on these engines the valves get close to the pistons all the time, having the valves start out even closer is a really good way to make it interfere during operation.
Are you sure your Bentley says that? Read again, and I think that youwill find that the 'd' =0.5mm is for a different diagram.
That is how it is for my 1985 Quantum Bentley. As far as I'm concerned that 'maximum' is an error, or at least it should also be linked to a minimum.
The 0.5mm is referring to the minimum thickness of the edge of the valve.
It is typical of the Bentley 'rag-mags'. They merely copied the same omission from the VAG. official mag. A lesson in plagerism if ever there was one 
VAG was only interested in the 1980's in the sale of new heads, hence the "Heads cannot be skimmed" proclamation.
It was of course a lie. Bulletin #4 in the VAG mag may contain ther truth, but alas someone took the info out of my copy before selling me it! My engine is living proof of the ability to skim and of going beyond the limit. 
However, assuming the valve seat hasn't sunk into the head, then if someone has the thickness of a new valve, the original depth can be found,; eg if original valves are 2mm thick, then they are flush 
If aftermarket valves are thicker than true OEM, then skimming valve face is in order. This is my next move when I take the head off, Not doing it until I need to though
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#25
by
Mark(The Miser)UK
on 24 Sep, 2011 13:25
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i guess they shaved the head even tho it was brand new?
I'd not be surprised if ChinaHead didn't put the seats at the right depth to start, or got a batch of thicker valves.
I didn't see this post as I started writing my post 7 hours ago and got called away
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#26
by
rabbitman
on 26 Sep, 2011 22:26
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Are you sure your Bentley says that? Read again, and I think that you will find that the 'd' =0.5mm is for a different diagram.
I just checked again and I'm 100% sure that what it means.
I'll take a picture of the diagram and wording and post it in the next day or two.
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#27
by
Mark(The Miser)UK
on 27 Sep, 2011 09:51
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This is what I have:
1982 to 1985 Quantum Bentley both 'd's on one page but under 2 diagrams
Source of depth 'd' Golf 1.6TD VAG manual 1982.
Source of valve thickness 'd' Golf1.6TD VAG manual 1982.
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#28
by
Mark(The Miser)UK
on 27 Sep, 2011 11:44
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Sorry those pictures aren't the best and the Image Host is not giving me the usual A3 sized picture.
Useing 'control and scroll' on your mouse together should enlarge the pics enough to see[color] that fig 17 and 16 in the Quantum Bentley are merely reversed order Fig6 and Fig7 in the earlier Golf VAG workshop mag, but each still has it's own 'd'
If the Golf Bentley omits the valve edge photo but still prints the quote, then it's another nail in the coffin of your Bentley bibles
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#29
by
gldgti
on 28 Sep, 2011 03:34
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If it were me, i'd probably replace those rode bearings and forget about the valve marks.... seen a lot worse :-)
Sadly, i think i've only ever seen one IDI diesel without some valve marks in the pistons!
As has been covered, the big thing if the head has been skimmed is to make sure the valve seat is cut and that the valve is cut back also (i think it was 'b' in those scans). The valve length should be cut back the same amount as the valve seat, otherwise the valve lift will be more than it should be, at all cam positions, hence the marks in the pistons.
