[Supras] HELP: Weired piston height

[berniek at technicaldevelop.com]

Bob:

    With the piston down by almost 1/8 inch, it was very easy to spot 
during crown wire brushing.  #1 and #6 come up together, and the outer 
portion of the crown of all pistons but #1 came right up to the deck 
height.   #1 being down in the bore stuck out like a sore thumb.  After 
seeing that I measured the crown to deck height differences between #1 
and #6 at several  heights in the bores, and found the difference to be 
the same in each instance, about .100". 

    Going to 15 PSI boost with a 57 trim turbo, 550 cc injectors, Lexus 
AFM, etc., etc., my better judgment indicates I should not take a chance 
with this situation.  The JDM short block I built will probably wind up 
in the car, unless anyone else on the list (in addition to the 
optimistic outlook of Bob Shapton) has had no problems for 100K (?) 
miles with a bent connecting rod.

    Looks like the short block removal will be relatively easy with 
everything else removed.  Any comments would be appreciated. 

    Thanks.

       Bernie

Bob wrote:
> Only you would have checked....
>
> Could manufacturing tolerances cause this or are the rest exactly the same?
>
> Bob
>
> -----Original Message-----
> From: supras-bounces at supras.com [mailto:supras-bounces at supras.com] On Behalf
> Of berniek at technicaldevelop.com
> Sent: Saturday, July 07, 2007 5:14 PM
> To: Supras at supras.com
> Subject: [Supras] HELP: Weired piston height
>
> Man, if I ever needed help from knowledgeable people in this good group, 
> now is the time.
>
> I got the head off my newly bought '91 turbo to lap the deck and install 
> a Cometic gasket and rebuilt head.  While cleaning the piston crowns, I 
> noticed that the first cylinder piston crown is about .100" lower than 
> the others.  Measuring it and piston 6 to the deck, the .100" additional 
> depth is always there!.  There is no vertical slop indicating bad 
> bearings or a bad wrist pin.  That was tested by turning the engine over 
> to pull #1 piston down in the bore, and then tapping down on its crown.
>
> All of the bores are just about at the factory initial size (3.270" 
> measured with an inside micrometer.  #1 piston crown looks fine.  All 
> are stock turbo pistons.  There are some very light scratches at the 
> backside of the bore but no top ridge in any of the cylinders. 
>
> This is the weirdest thing I've ever seen.  Is there any chance that it 
> was assembled with a piston or rod from a different year?  The engine 
> ran fine before disassembly.  Any and all suggestions would be very much 
> appreciated. 
>
>        BernieK
>
>
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