hmm, thats a thinker(help with rough running engine)

[Astra Dan]

Cool, I said it sounded like it was missing a beat the other day! We're all brilliant.

[ChrisB]

this is almost as good as me fitting my pistons round the wrong way.

Hopefully they don't have off centre pin alignment like most pistons do! Going to be very nasty on the thrust side of the skirt if they do.

[DarrenH]

the stock XE pistons here on the desk appear to be central.

[ChrisB]

The one I have here I make to be very roughly 1mm offset. Just a rough measurement by drawing round it, marking down the centreline of the pin and then measuring cross point, so could be wrong.

I'd certainly double check though.

[DarrenH]

well you got me thinking anyway because the XE pistons have an arrow on the crown which has to point to the cambelt end when fitted.

[JohnnyB]

This is news to me too - my pistons are on the right way around before anyone asks - why do they have "off-centre pin alignment"?

[DarrenH]

to help stop the piston rocking on the power stroke i imagine.

[ChrisB]

Reduces piston rattle over TDC. Very few production engines have dead centre pin aligment. Not actively looked, but the only one I know of is the Subaru Impreza engine (not sure which variants). I guess due to homologation rules.

[JohnnyB]

Cheers, I better look this one up!!

[DarrenH]

ok, found out today omega gudgeon is central. omega exhaust cutouts are just over 30mm (inlet valves are 33mm) so i am at risk if the belt jumps a few teeth or i ask for more cam lift.

[dathers]

Hopefully they don't have off centre pin alignment like most pistons do! Going to be very nasty on the thrust side of the skirt if they do.

I was also gonna mention this,its to reduce stresses and wear,so the wrong way will INCREASE wera,not good.
Dave