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> Crack, or normal casting?
74ravenna
post Sep 24 2016, 10:04 AM
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Is this a superficial blem in the casting?
Once magnified it appears to be but I just want to get some knowledgeable folks opinion.


TIA
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stugray
post Sep 24 2016, 10:08 AM
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casting imperfections.

They are covered in them.
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TheCabinetmaker
post Sep 24 2016, 10:08 AM
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What is that we are looking at?
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dangrouche
post Sep 24 2016, 05:16 PM
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QUOTE(The Cabinetmaker @ Sep 24 2016, 09:08 AM) *

What is that we are looking at?

looks like underside of one of the cylinders
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injunmort
post Sep 24 2016, 05:24 PM
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is that the cylinder spigot?
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earossi
post Sep 24 2016, 07:15 PM
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Appears to be a surface crack in the spigot on a cylinder. The problem with surface cracks is that with temperature cycling, they will usually propagate. The way to deal with any crack is to grind out the crater until the crack vanishes. Surface cracks in castings usually grind out with very little effort. But, if the crack is found to have propagated through most of the thickness of the casting, you may suffer failure of the spigot.
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stugray
post Sep 25 2016, 01:28 AM
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QUOTE(earossi @ Sep 24 2016, 07:15 PM) *

Appears to be a surface crack in the spigot on a cylinder. The problem with surface cracks is that with temperature cycling, they will usually propagate. The way to deal with any crack is to grind out the crater until the crack vanishes. Surface cracks in castings usually grind out with very little effort. But, if the crack is found to have propagated through most of the thickness of the casting, you may suffer failure of the spigot.


If that was a crack, my engine would have fallen apart already.
Mine is covered with them.
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veekry9
post Sep 25 2016, 02:09 AM
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Shrinkage of diecast surfaces,a subject of depth and much study to this day.
A high volume,water-cooled,steel die casting mold,was used to make the cases.

Some light reading: (IMG:style_emoticons/default/biggrin.gif)
https://www.google.ca/search?q=shrinkage+of...quIeNvvlNN5M%3A

Shot sleeve barrel:
https://www.google.ca/search?q=die+casting+...aMOSyoRZqTjM%3A

Metallurgy this year: (IMG:style_emoticons/default/smile.gif)
https://www.google.ca/webhp?sourceid=chrome...+aluminum+alloy

Method to produce castings to fine tolerance and finish,economically,short run:
https://www.google.ca/webhp?sourceid=chrome...ing&tbm=vid

/

Look!
There's more:https://www.youtube.com/results?search_quer...+die+cast+metal
https://scholar.google.ca/scholar?q=solidif...bJdBe8QgQMIGjAA

To answer the question of why it looks like that,and the other why,'draft'.
(IMG:style_emoticons/default/smile.gif)

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74ravenna
post Sep 25 2016, 04:51 AM
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Its the top of the engine where the cylinder head meets the case.
I'm going with casting imperfections.
This is my first go around with taking one of these apart and i've never seen the engine clean!

Thanks all.

Steve
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rgalla9146
post Sep 25 2016, 05:50 AM
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QUOTE(74ravenna @ Sep 25 2016, 06:51 AM) *

Its the top of the engine where the cylinder head meets the case.
I'm going with casting imperfections.
This is my first go around with taking one of these apart and i've never seen the engine clean!

Thanks all.

Steve


I agree.
Those rise from the surface.
A crack would be hollow into the surface.
Some of the responses are 'interesting' though !
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earossi
post Sep 25 2016, 06:27 AM
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QUOTE(rgalla9146 @ Sep 25 2016, 06:50 AM) *

QUOTE(74ravenna @ Sep 25 2016, 06:51 AM) *

Its the top of the engine where the cylinder head meets the case.
I'm going with casting imperfections.
This is my first go around with taking one of these apart and i've never seen the engine clean!

Thanks all.

Steve


I agree.
Those rise from the surface.
A crack would be hollow into the surface.
Some of the responses are 'interesting' though !



Good discussion. On my computer I can't see the depth of the crack. If it is simply a shrinkage crack, then it should grind out easily with a Dremel tool. But, if it is a through crack, it's a different story.
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veekry9
post Sep 25 2016, 06:48 AM
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Not a crack,it's a 'shrink riser'.
The mold of the part is(was),a polished steel surface of <63rms finish,nearly mirror.
As the molten metal cools and changes volume,it shrinks,creating stress risers,and ridges.
A superficial blemish,and acceptable in it's application,which may appear as a crack,to the untrained eye.

https://www.google.ca/webhp?sourceid=chrome...e+for+aluminium
(IMG:style_emoticons/default/smile.gif)
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74ravenna
post Sep 25 2016, 07:03 AM
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QUOTE(veekry9 @ Sep 25 2016, 08:48 AM) *

Not a crack,it's a 'shrink riser'.
The mold of the part is(was),a polished steel surface of <63rms finish,nearly mirror.
As the molten metal cools and changes volume,it shrinks,creating stress risers,and ridges.
A superficial blemish,and acceptable in it's application,which may appear as a crack,to the untrained eye.

https://www.google.ca/webhp?sourceid=chrome...e+for+aluminium
(IMG:style_emoticons/default/smile.gif)
/


"which may appear as a crack,to the untrained eye."

Exactly the situation here.

Thanks all!
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76-914
post Sep 25 2016, 07:16 AM
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I think it happens on all Aluminum engines. The Subaru engine has them as well.
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Mikey914
post Sep 25 2016, 09:47 AM
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Only one way to tell for sure. File the imperfection flush with the surface and put a drop of penetrating dye on it. A casting imperfection will not reappear.
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bretth
post Sep 25 2016, 10:53 AM
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I read about using a torch to briefly heat up a suspect crack in magnesium, and you will see it open. Not sure if this works on AL alloys or not.
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Mikey914
post Sep 25 2016, 02:17 PM
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Wouldn't personally use a torch on this, too many things that can go wrong.
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earossi
post Sep 25 2016, 02:38 PM
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Hitting magnesium with a torch will ignite it; so, suggest you not do that. Many years ago, VW used to make magnesium engine cases. One of the reasons they went aluminum was the occasional fire due to magnesiums flamability.
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veekry9
post Sep 25 2016, 09:56 PM
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https://www.youtube.com/watch?v=AiYnDskFxTo

Burning metal! (IMG:style_emoticons/default/blink.gif)

VW/Porsche made the Type4 engine from aluminum for it's tensile strength,not for it's 'unflammabilty'. (IMG:style_emoticons/default/dry.gif)
Heated magnesium castings to fit interference bearings,circa '70s,did not catch fire back then.
Intentionally lit hair-thin magnesium and titanium turnings,and without the added heat of the torch,went out.
A puddle of molten magnesium can be lit up with an oxygen rich atmospere and added torch heat.
So,yeah,the metal can light up,but,it isn't like it will spontaneously combust.
Putting a torch to a casting long enough to melt,will result in a puddle of magnesium on the floor.
It would be very difficult to ignite a casting such as the VW cases,the wall thickness and mass too great.
Welding the material with ox-ac in the past was a difficult job,no doubt,but quite possible tho.

https://www.google.ca/search?q=oxygen-acety...gA&dpr=1.75
https://www.google.ca/webhp?sourceid=chrome...er&start=10
https://www.google.ca/webhp?sourceid=chrome...agnesium+solder
https://www.google.ca/webhp?sourceid=chrome...ing%20magnesium
https://www.google.ca/webhp?sourceid=chrome...sting+magnesium
https://www.google.ca/webhp?sourceid=chrome...e+sand+casting+
https://www.google.ca/webhp?sourceid=chrome...s+burning+metal
https://www.google.ca/webhp?sourceid=chrome...e%20ingredients

The round spots on the die-cast magnesium engine parts:
https://www.google.ca/search?q=ejector+pins...RLODYQQ_AUIBigB

/
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earossi
post Sep 25 2016, 11:35 PM
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QUOTE(veekry9 @ Sep 25 2016, 10:56 PM) *


https://www.youtube.com/watch?v=AiYnDskFxTo

Burning metal! (IMG:style_emoticons/default/blink.gif)

VW/Porsche made the Type4 engine from aluminum for it's tensile strength,not for it's 'unflammabilty'. (IMG:style_emoticons/default/dry.gif)
Heated magnesium castings to fit interference bearings,circa '70s,did not catch fire back then.
Intentionally lit hair-thin magnesium and titanium turnings,and without the added heat of the torch,went out.
A puddle of molten magnesium can be lit up with an oxygen rich atmospere and added torch heat.
So,yeah,the metal can light up,but,it isn't like it will spontaneously combust.
Putting a torch to a casting long enough to melt,will result in a puddle of magnesium on the floor.
It would be very difficult to ignite a casting such as the VW cases,the wall thickness and mass too great.
Welding the material with ox-ac in the past was a difficult job,no doubt,but quite possible tho.

https://www.google.ca/search?q=oxygen-acety...gA&dpr=1.75
https://www.google.ca/webhp?sourceid=chrome...er&start=10
https://www.google.ca/webhp?sourceid=chrome...agnesium+solder
https://www.google.ca/webhp?sourceid=chrome...ing%20magnesium
https://www.google.ca/webhp?sourceid=chrome...sting+magnesium
https://www.google.ca/webhp?sourceid=chrome...e+sand+casting+
https://www.google.ca/webhp?sourceid=chrome...s+burning+metal
https://www.google.ca/webhp?sourceid=chrome...e%20ingredients

The round spots on the die-cast magnesium engine parts:
https://www.google.ca/search?q=ejector+pins...RLODYQQ_AUIBigB

/




Without this turning ugly, I suggest that you Google "magnesium fires". If you go back to the early days of the Beetle, VW used magnesium for its cases. The magnesium did not "spontaneously combust". Fires usually started from other faults such as fuel leaks or electrical fires. Once the engine saw fire, the magnesium would combust. I saw one burn like that when I was in college back in the 60's. And, water will not extinguish a magnesium fire. You let them burn until they run out of fuel. Or, you can foam the fire, though I never did witness that.

And, I believe that VW went to aluminum because it was less expensive than magnesium, and more stable. Not for its combustibility as you pointed out.
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