Piston Q

[jdbubb at verizon.net (Dan Bubb)]

You know another possibility is to have the tops of the pistons machined 
down by 1.35mm (assuming a TDI crank is 95.5 stroke).
It won't effect the strength of the piston crown because you'd only be 
machining the perimeter and not the center which is the area subjected to 
the most heat and requires the most strength.
OTOH, the top piston ring can't be too close to the top of the piston. There 
are possible overheating effects and it will also weaken the top ring land 
and any detonation or pinging could possibly collapse the top ring land (top 
perimeter) of the piston clamping the top ring and eliminating its sealing 
ability. You'd have to consult somebody with more experience than me on 
something like this. I only know that turbo pistons, subjected to higher 
pressures and more heat, routinely have the top piston ring further down the 
piston. Perhaps somebody like Colin at TT would have some experience with 
this.
Dan

From: "Mtl-Marc" <marc_scirocco@xxxxxxxxxxxx>
To: "'Dan Bubb'" <jdbubb@xxxxxxxxxxx>; <scirocco-l@xxxxxxxxxxxx>
Sent: Monday, May 07, 2007 6:53 PM
Subject: RE: Piston Q


Thanks for the info Dan, I'll call my machine shop so they can
machine/balance my pistons/rods.

Here is what I had in mind for headgasket http://www.headgasket.com

Cheers.

Marc

> -----Message d'origine-----
> De : Dan Bubb [mailto:jdbubb@xxxxxxxxxxx]
> Envoyé : 7 mai 2007 09:47
> À : marc_scirocco@xxxxxxxxxxxx; scirocco-l@xxxxxxxxxxxx
> Objet : Re: Piston Q
>
> Well, technically the piston should have a shorter pin
> height, by half the difference in stroke between the TDI
> crank and the 2.0L crank, 1.35mm I think.
> IIRC the ABA steel head gasket is 1.65mm thick compressed.
> So, two of them stacked would give you about 3.3mm or 1.3mm
> above your piston which is just about the right piston to
> head clearance.
> I don't know if that's a good solution though. I'd wonder how
> well they would seal if the embossing on the two gaskets
> didn't line up close enough.
> If you go with a copper gasket measure the piston protrusion
> from the block using a micrometer or caliper. Add
> .040"minimum to that for the final gasket thickness.
>
> As a minimum, after you modify the pistons for oil squirter
> clearance, you need to get them rebalanced. You can modify
> them yourself, but I'd be striving for an identical cutout in
> all the pistons.
> Dan
>
> From: <marc_scirocco@xxxxxxxxxxxx>
> To: <scirocco-l@xxxxxxxxxxxx>
> Sent: Monday, May 07, 2007 8:47 AM
> Subject: Piston Q
>
>
> >I installed my TDI crankshaft in my 9a block this week-end hoping to
> >get 2.1l of 8v power ;-)
> >
> > The crankshaft spins freely without hitting anything, so
> that is good.
> >
> > However, there are two snags as I see it.
> >
> > 1. the piston stick about 2mm out of the cylinder at TDC.
> > Can I safely run 2 head gaskets to bypass this problem?
> > I have seen a shop in the norteast that can make me a
> copper head gasket, Perhaps this can be a more permanent
> solution in the long term.
> >
> > 2. on the bottom stroke, the piston hit the oil squirter.
> > There is already a notch in the piston skirt for the oil
> squirter. But I need a bigger notch.
> > Do I need a machine shop to do it or can I just enlarge the
> notch at home with my die grinder?
> >
> > Thanks
> >
> > Marc
> >
> >
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