or top end, valve stem seals etc
Seems to make sense. As aluminium expands faster than most metal so it should close the gap as the engines warmed.
If your block is aluminium it will expand at the same rate to a certain extent leaving you with excessive gap still
Wouldn't say you need track day heat An engine should only get so warm because of your cooling system? So potentially overcooling? Keeping the engine too cool for the pistons to expand. At the simplest anyway
Or a rebuild again at the worst. Steel sleeves to stop the cylinder walls expanding away from the piston?
I hope what I've wrote makes sense
mine has that diesel like sound sometimes if i jab the throttle @ idle paul (the corsa piston engine and this untouched stock CGA3) its just the sparkmap i think mate (running plenty of advance at low load)
and my corsa piston engine smoked on 1st build if you remember, and i thought "running in" the freshly re-bored and honed bore would bed the rings in, but no chance and it was only when i stretched the expander rings so that the ends touched (you can see a 2mm gap in the pic below), and i could feel the oil control rings actually bite into the bores, that it stopped smoking instantly ,
you can see on arnold,s mallory vid that mine was,nt smoking eh (till i cooked the engine )
and stani,s was blowing that fuse when his nistune board was shorting on the ecu casing iirc
7kg should be plenty paul, mine were 2kg before and 4 to 5kg after (but that was with the piston half inserted upside down, without the skirt friction and purely oilring friction tho)
my compression was always fine regardless, and with the old cast iron 1 piece oil control ring there were no problems years ago (they were just as springy as the 2 compression rings)
but these 3 piece ones rely on the tiny feet at the bottom of the expander ring to physically "push" the 2 oil control rings into the bore eh
these forged pistons are prob a different type of Alu and could expand at a higher rate than the block and steel liners, hence why JE recommends more piston-bore clearance as the power/heat increases.
the intense combustion heat (higher up the power/torque curve = more heat generated) is transferred to the block, head and pistons. on trackdays u spend more time at the high end.
the block and head is directly cooled by the 80-90C coolant and brief cool intake air and maintained by thermostat and oversized radiator. its maintained at 80-90C to balance the most combustion efficiency before the oil starts to degrade or the metal deforms so shouldn't usually be over-cooled unless u intentionally remove the thermostat.
the pistons on the other hand are only cooled via conduction through the thin rings to the bores and the hot oil spray underneath and briefly by the cool intake air so will become hotter than the block.
Very true some swap out their thermostat for cooler opening ones too.
Just throwing ideas at you. Do you know what type of alu piston you have? 4032? 2618? The type affects their heat/expansion coefficient. Depending on their silicon percentage.
If JE are recommending a larger gap then I'd say they're 2618 their low silicon percentage allows for more heat expansion iirc. 4032 are the other way round. Could be worth looking into ?
Nice spot paul. Hopefully thats perked you up a bit
yeah good thing I decided to remove the turbo inlet pipe to access the alternator better otherwise I wouldn't of spotted the obvious fractured bracket. its a relief and one less thing to worry bout and made me less depressed
Just one more fuse to buy then
Think these are them?