[Vwdiesel] Piston fit in block ---- ( when reboring ).

[paulr]

A cam ground piston is slightly elliptial.  The skirts
(thrust area) are just slightly larger than the wrist
pan faces.

The "tighter" fit on the thrust faces keeps the noise down on
a cold engine.   As the piston heats up, expansion occurs
on the wrist pin (non-thrust) sides. You get a nice quiet low
noise start up, and still have room for themal expansion along
the wrist pin faces. There's actually quite a bit of heat transfer
between the thrust surfaces and the cylinder block...

Regards,

Paul

2000 Gold TDI

H.Hagar wrote:
> I consider myself a good reader (no Borge accent) and a good listener.
> 
> So when Gavrik and I dropped in on a German mechanic up here I listened
> real carefully
> 
> Gavrik was concerned about ring seating and oil consumption  and I heard the
> German say that VW diesels are not a straight bore.  It is like cone or funnel.
> The top part is smaller than the bottom. ---Is that true ?.
> 
> Some of you may have missed it when Loren mentioned using Oven cleaner on
> manifolds ----   great Idea ---  I got some left over Mr.Muscle. Got a self cleaner now.
> 
> The 2 thou piston fit I got from a friend. That is a tightie.    My GM book for
> the V 8  say 5 thou.   
> 
> Val Christian mentioned to be careful when doing compression test  -- she may
> fire if you do it wrong. ----I did hundreds of tests wrong .  Yes I turn off the fuel
> but I was in the habit of squirting lots of AD-100 in there to see if the rings were
> the problem.  ----- bang there goes a perfectly good gauge ?. (he is right).
> 
> Now for the pistons they are special --- and do not expand according to
> Shepherd math.      What is a camground piston ?    And one member mentioned
> that his piston was marked 10 on top --I think that means oversize. Not fit.
> 
> I have a 1960 Landrover 2.25L gasser with knurled piston skirts. Never did
> find out if that was factory done. I got it near new. A very good engine that was.
> Same block and crank as for the diesel model.
> 
> Grind the crank and it has to be marked gasser only. They are fuzzy in the UK.
> 
> All the diesels I looked at had so little wear  --- that I never had one rebored.
> Just new rings and a valve job.And all was fine --- still is.Do a lot of heavy
> duty honing and fitting of pistons.Find a tight piston and hone like crazy.
> 
> Hagar.
> _______________________________________________
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> Vwdiesel at vwfans.com
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> 

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Paul Reich                Electrical Engineer

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