How to determine notches regarding head gasket type

[theman53]

I only asked you to prove what you said man..

You said no because we are not worth your time..

Why do you post here then??

Enough. You are putting words into his mouth, he never said anyone here was not worth his time. Last warning.

[745 turbogreasel]

If yo look at a  piston with long term  EGT damage,  it is almost always at the edge of the piston  crown is it not?
VW was building 60HP engines with a 40K warranty,  I doubt they were too worried about it.

As for Libby's cost-benefit habits,  I can say he  advised me  correctly  on fixing my throttle arm issues, and I never gave the SOB a  dime, a beer, or even or a reacharound.

[libbydiesel]

Hey, where's my dime and who are you calling an SOB? [headed to the FAQ to find that form...]

What conclusion are you coming to WRT EGT damage?  That sharp edge is the most prone to heat damage and I would have to assume that additional quench would only assist in reducing it.  

[745 turbogreasel]

That is pretty much my conclusion too.

[Jaceb-GLI]

It is almost inconceivable to me that there is an IDI still running with the original  headgasket.

hey hey mine is original.

[Dakotakid]

Hey, I've actually got an original gasket car as well. Although it hangs out in storage (92 Eco).
Do we get a prize? Perhaps Commander Putin will come by and congratulate us?

[8v-of-fury!]

I only asked you to prove what you said man..

You said no because we are not worth your time..

Why do you post here then??

Enough. You are putting words into his mouth, he never said anyone here was not worth his time. Last warning.

Lol what? Are you serious? What was wrong with that? How come everyone is not held to the same standards around here?

[Mark(The Miser)UK]

The number is important... Too thin and pistons hit stuff. Too thick and you sacrifice compression.

The compression difference is not really of issue.  The other two factors are 'squish and quench'.  Squish establishes the correct turbulence, again probably not an issue on a pre-chamber diesel.  Of particular issue, tho, in a TD is quench where a significant amount of heat is transferred from the piston crown to the more cooled cylinder head.  Increasing the space between piston crown and head at TDC will have negatively affect quench and cause the piston crowns to run hotter.

EDIT:16  posts since I started writing this whilst doing other jobs, so I my need to edit but it's 3am here  and I'm too tired...!

These are strange comments Andrew. I feel I have to comment because you are held in high esteem  by your followers, due to your vast experience, you my be having an off day and unintentionally misleading your members:

1)A bit rash to say that compression changes by changes in gasket re unimportant especially as most engines are getting quite old now and starting issues are likely to be waiting in the back ground with these IDI's.

2) Required turbulence is, and has been since Ricardo optimized it back in the 1920's at a rotational speed of 7 or was it 8 times the engine rpm. using chamber size and throat combo.


3) If 'quench'  had anything to do with these IDI engines, how do you account for the effect or no effect, of  using different materials for headgaskets.
For example for some unknown reason I have a few genuine 1 & 2 hole asbestos gaskets [I use/require 3 hole], which surely insulate the head differently to the more usual 'plastic' ones, or then there is the 1.9 metal one, which must allow for greater heat transfer out of the head.
You've referred to this squish and quench stuff before. All I've ever found is gasser research and DI diesel references to the gasser research  'possibly' being applicable.
What references do you possess or, better still colaberating experience of these effects  do you have? I would suggest that the process of 4 strokes act to quench piston temperatures, along with my factually correct retardation of timing... Surely there is more heat radiating from the head, and especially the precup, than from the rapidly reducing heat in a decompressing piston chamber. Come to think of it  an engine with the combustion chamber in the piston might benefit from heat transfer across the void to the cylinder head...

[745 turbogreasel]

3) If 'quench'  had anything to do with these IDI engines, how do you account for the effect or no effect, of  using different materials for headgaskets.
For example for some unknown reason I have a few genuine 1 & 2 hole asbestos gaskets [I use/require 3 hole], which surely insulate the head differently to the more usual 'plastic' ones, or then there is the 1.9 metal one, which must allow for greater heat transfer out of the head.

Headgaskets are  spec'd  by compressed thickness.  a 3 notch metal one installed thickness is the same as a  3 notch  fiber which will have been thicker on the shelf.
MLS ones seal better for longer and withstand  greater stress than fiber ones, hence have replaced them in almost  every automotive application.  They may or may not  transfer heat differently, but the difference  for better or worseis  far outweighed by the reliability gained by going MLS.

When you say 'plastic', you are referring to the Viton coating on an MLS gasket correct?

[libbydiesel]

I always measure the piston protrusion and use the correct thickness gasket.  I measure the piston protrusion by carefully scrubbing off the carbon from the piston crown and use a straight edge across the surface of the crown parallel to the wrist pin bore.  I then use feeler gauges to determine the protrusion of the piston on both sides.  I write down the larger of the two measurements and proceed to the next piston.  After measuring all four I find the highest protrusion and use that to determine the gasket for use.  

I have a dial indicator and adjustable magnetic base and have used it a couple times to measure protrusion but I find the feeler gauges to be more accurate.  The arms of the dial indicator base intrinsically have some flex to them and it is necessary to move the mount over to the block to zero it and then back to the piston and I find that moving the base can skew the reading.  A test to see if the reading is skewed is to move the needle to the block, zero it, move it to the piston, measure it and then move it back to the block to see if goes back to zero correctly.

For a bit of time I have been planning on taking a machined flat that is 3/8-1/2" thick and drilling and tapping it to 8x1.00 in the center so I could thread in my pump timing dial indicator adapter.  I believe that using that along with two equal thickness valve shims would be faster than the straightedge/feeler gauges and more accurate than the magnetic base with the dial indicator.  In order to use it, place the valve shims under the ends of the flat on top of a true flat surface and zero the dial indicator.  Then place one valve shim on either side of the piston and the flat across like a bridge.

On a rebuild, if the block is not skimmed at all, it is not uncommon to find that the piston protrusion is below the spec for the 1-notch gasket.  New pistons typically move the wrist pin bore closer to the crown in order to allow for surfacing the block head gasket surface.  Reconditioned rods can also reduce the piston protrusion.  Several years ago, I had one rebuild that had protrusion to low for a 1-notch and I didn't figure that out until I had the bottom end assembled with the pistons in the bores.  It really stunk to have to disassemble it all (thankfully I had purchased ARP rod and main fasteners) in order to get the head gasket deck skimmed more.  Since that happened I have rebuilt several of these engines and taken a different approach in order to avoid that issu.  Since then, the protrusion has come out right where I wanted it each time.  When rebuilding one of these engines I like to measure the piston protrusion with the old pistons and the reconditioned rods before taking the block to the machine shop for boring.  I then measure the wrist pin bore to crown height on the old and the new pistons.  Once I know the protrusion of the old pistons and the wrist pin bore to crown measurement of both, simple math lets me know how much to tell the machinist to trim from the block head gasket surface.  I typically make the protrusion fall right in the upper range of the two notch as the AAZ 1-notch gasket is less available and more expensive and if there is any issue with the machining or measuring the odds are still good that I will not fall outside the range for all three.  I still re-measure protrusion after getting the block back from the machinist in order to make sure of the measurement before ordering the head gasket.  

[Mark(The Miser)UK]

3) If 'quench'  had anything to do with these IDI engines, how do you account for the effect or no effect, of  using different materials for headgaskets.
For example for some unknown reason I have a few genuine 1 & 2 hole asbestos gaskets [I use/require 3 hole], which surely insulate the head differently to the more usual 'plastic' ones, or then there is the 1.9 metal one, which must allow for greater heat transfer out of the head.

Headgaskets are  spec'd  by compressed thickness.  a 3 notch metal one installed thickness is the same as a  3 notch  fiber which will have been thicker on the shelf.
MLS ones seal better for longer and withstand  greater stress than fiber ones, hence have replaced them in almost  every automotive application.  They may or may not  transfer heat differently, but the difference  for better or worse, is  far outweighed by the reliability gained by going MLS.

When you say 'plastic', you are referring to the Viton coating on an MLS gasket correct?

  Hi,
Sorry for the vagueness. For 'plastic' I was actually referring to the run of the mill later fibre ones, which, incidentally seem to compress more.
It was only, what must be  the vastly contrasting  heat transfer properties between asbestos, non asbestos, and Mls gaskets, which may, or may not  influence how an engine performs, or heats, or indeed cools in this context.
Anyway where is the IDI research on the influence of quench/squish? Patents office perhaps?
 

[745 turbogreasel]

AFAIK all IDIs  of every brand are tight squish motors where the piston  protrudes above deck.  There must be  a reason. 

[Mark(The Miser)UK]

AFAIK all IDIs  of every brand are tight squish motors where the piston  protrudes above deck.  There must be  a reason. 

To get most of the air into the swirl chamber?
 
A simple calculation should give us the difference in rotation of the air mass in the chamber between virtual touching of piston to head, and, perhaps pistons that are a mm or so lower and flush with the deck. Ricardo seemed to think [heck he did a lot of research] or rather knew that a certain number of swirls performed best.
 
Has the protrusion also to do with manufacture of a gasket, initially of asbestos, later of other fibers, that needed encasing in that thin shield of metal to void breakup.

Maybe the AAZ missed an opportunity to drop the height of the pistons and use a gasket of a few thou. Are there graphs of strength of clamped gaskets and their thickness...
Could some air being left outside the chamber actually help complete late combustion, as the pistons decend?

Of course the TD and late N/A's all had the oil cooling  under the pistons, taking the heat in the other direction.

I'm just trying to think, did the 1.4 n/a Citroen AX  have flush pistons? They had wet liners, used the same injectors as the VW, and got 80+mpg genuine. That was Al block/head, whilst the later 1.5 changed to cast iron block.

[theman53]

I have talked to a couple machinists, granted they are not experts, and they have said the combustion is supposed to take place in the prechamber. To add the volume to the top of the piston area for no reason can retard the combustion event or add dwell to the flame travel as it can slow the burn. If what they say is true then I think what Libby and 745 have commented on makes sense. The "quench" "squish" etc isn't in the prechamber and the added burn time is on top of the piston, therefore making it hotter there than it normally would be, but a lower temp overall as the event contained in the prechamber would be a quicker hotter burn.

All theory and guessing from the machinist and my head, but it makes sense to me. I think we have a great discussion here.

[JerryGTD]

Lots of good info in this old thread... http://www.vwdiesel.net/forum/index.php?topic=8369.0