[Vwdiesel] three questions...

[Dana Morphew]

...Also the potential for expansion (used for racing or normal driving?) of 
the given piston type (cast or forged) and probably the metallurgy are 
considerations.  I put forged pistons in mine when I rebuilt.  The machinist 
bored for a 0.003" clearance.  The piston manufacturers wanted 0.004" in a 
racing application.  After I told them about the intended use, 0.003" was 
their recommend.  The Mahle pistons are cast and the Bentley specs are for 
their use.

Dana

 

 > It will almost ALWAYS add to the life since you're starting with a new 
bore,
> less slop, zero wear, etc.  The catch is to MAKE DARN SURE the machinist
> know's what's what when boring these engines!!!!!!!!!
>   Mine wanted to bore for .0018 clearance.  Specs call for .001 and 
> the wear LIMIT is called out at .0024 inch.  He was going to give me a 
> FRESH bore that was more than HALF GONE already!  The reason 
> was because that's what some other shop in town wanted.  (No chance 
> of seizing a piston that way I suppose.)  I had to show him in the Bently
> manual the proper clearance.  He wouldn't believe it could possibly be
> tolerated that tight.  ALWAYS ask what tolerences they are going to bore to an
> demand no more than .0012".
>   Yes you always need new pistons to bore a block.  I suppose you could 
> scrounge up some used, oversize ones but that's kind of defeating the 
> purpose.  In fact you need the pistons BEFORE you take the block in to 
> be bored.  They mic the pistons and then bore and hone to size FROM 
> your piston's measurement.  :)
>      Loren