S16 Stroke Question

[Mr Bob 1]

I had an accident at the end of novmeber that done something to the timing of my s16s engine, now I have it back from the bodyshop I have took the timing belt out and cylinder head off, I found the aux belts got pushed off the crank pully and got tangled up in the timing belt which has jammed and snapped.

 

Once I got the clyinder head off I was checking the pistons for damaged and I noticed a black ring round the top of the clyinder:

 

 

Which I thought was normal, when i was looking into adding an 88mm crank I read on here the piston falls 2mm short of the top of the block at TDC, but as I turned it round by hand I noticed the piston sits flush with the block.

 

 

I have no history for this engine, so I'm wondering is my understanding of it incorect and this is normal? or is it soemthing to do with it not having the head/timing belt on? or has a 88mm crank been added at some point?

 

Thanks

Bob

Edited March 2, 2011 by pug_ham
Image filesizes, 800 x 600 & 160k max.

[Tom Fenton 1,542]

The black ring you can see is the area on the piston known as the top ring land. The shiny surface is caused by the piston rings running on the bore of the block. The piston itself runs closely in the block, but the top land area does not contact. Hence what you see is totally normal.

[Mr Bob 1]

So when I read on here the piston falls 2mm short of the block thats measured from the piston ring and not the piston crown?

[welshpug 1,657]

its 1mm roughly that they are clear of the deck, so add 2mm on the stroke and they'll come right up, possibly protrude into the gasket space.

 

they are perfectly flat topped which is why you can fit an 88mm crank (plus nice big valve reliefs), the later gti6 used a dished piston and the outer circumference of the piston came right up to deck height and have much smaller valve reliefs.

[Mr Bob 1]

its 1mm roughly that they are clear of the deck, so add 2mm on the stroke and they'll come right up, possibly protrude into the gasket space.

 

Are we talking piston rings or crowns here as the piston rings fall 2mm short (which leaves the top ring land in the picture as tom said) but the crown sits flush with the deck (as in the picture), thats normal then?

 

Sorry for the repeat I'm just want to make sure

[welshpug 1,657]

the top of the crown, in your pictures above the pistons are not flush with the deck.