Expanding Pistons

[ENSMR2]

So you buy a set of pistons say 86mm or 87mm.

But you measure them and they are lower 85mm.

This is because they would expand as it heats up.

Is there any way of telling how much they'll expand by?

My pistons I assumed were 86mm. Measured them and they are under that (so they'll expand) on the side of the box there is a circle with a line going through it and next to it it says 87. I guess this refers to the size of the pistons.

Crap. No 2bar boost for me then! even with a TW block!

Just want to make sure I know for sure they will expand to 87mm and not 86mm.

No idea what to do now. I'm gonna use them anyway and just laugh all the way to the nut house if the block cracks lol

Any idea peep's?

N

[aaronjb]

I thought they were meant to come with a sheet of accurate (and I mean accurate) measurements for your machinist to use?

[Quigonjay]

probably too obvious for this to be right
i would have thought that the measurement on the box is there expanded size and minus the measurement you took is the amount they expand by?

[Ian Geary]

Is the 86mm 87mm or whatever including the width of the rings?

Maybe the pistons are slightly smaller to accomodate these?

Just a thought, but could be up the wrong tree completely

Ian

[ENSMR2]

I've measured the skirt and that is 86mm. Mark tells me that this probably means my pistons are 86mm ones as the skirt doesnt really expand and the crown would expand ot match the skirt.

Opinions?

[Bender Unit]

What make are then Ens?

[ENSMR2]

What make are then Ens?

TODA

[^Trickster^]

Pistons are oval because the sides where the wrist pins are tend to expand more than the skirts and they become round when running.

The spec sheet will show where measurements are taken from.

The silca content normally dictates expansion ammount, but its normally thousanths of an inch.

Sound like 86mm to me The bores are bored to allow for skirt - cylinder clearances, normally 0.0025-0.0035 inch

Graeme

[ENSMR2]

Pistons are oval because the sides where the wrist pins are tend to expand more than the skirts and they become round when running.

The spec sheet will show where measurements are taken from.

The silca content normally dictates expansion ammount, but its normally thousanths of an inch.

Sound like 86mm to me The bores are bored to allow for skirt - cylinder clearances, normally 0.0025-0.0035 inch

Graeme

Not so sure.

The rings have 87 on them also just like this

Seems they are 87. no sheet with them.

[Steve Horrocks]

does that not say 82.00 N?

poss the internal dim of the rings?

pistons should be measured at the skirt 90° to the gudjon pin

[GT Rich]

Steve your smart @rse!

Rich

[ENSMR2]

does that not say 82.00 N?

poss the internal dim of the rings?

pistons should be measured at the skirt 90° to the gudjon pin

Image Replaced With URL For Quote http://www2.tech.purdue.edu/at/courses/ ... ameter.jpg

Nope, it says 87.00 lol/ The . is close to the 7 so in the crappy picture it looks like a 2 lol.

The skirt was measured at 86. However that is using a ruler. I don't have fancy measuring tools like the owner of that hand does lol.

The box and the wrapping for the rings say 87 so it's got to be 87.

So my displacement will be 2211cc.

[FreeFall]

I'm no expert but wouldn't the displacement be relative to bore size rather than piston size?

i.e. The volume of air in the cylinder according to the length of stroke multiplied by four?

[FreeFall]

[anna]

FYI the circle with the line through (phi) is the standard symbol for diameter.

Also - we need to get the block rebored on our SC, but the machine shop won't do it until we have the pistons so they can measure them individually and then bore to fit.
If you're putting new pistons in, it might be worth taking the block and pistons somewhere for precision measurement - if nothing else, you can match up the cylinders with the best matching pistons.?

[aaronjb]

The skirt was measured at 86. However that is using a ruler. I don't have fancy measuring tools like the owner of that hand does lol.

The box and the wrapping for the rings say 87 so it's got to be 87.

I hope you or your builder will be measuring them properly (with a set of verniers) before touching your block

[Bender Unit]

I'm no expert but wouldn't the displacement be relative to bore size rather than piston size?

lol do the maths feller.

A larger piston will mean a larger bore is needed to accomodate it - so displacment goes up.

Also you can increase displacment by stroking meaning bore size is not the sole deciding factor in displacement

[FreeFall]

ENS,

I have a set of vernier calipers if you want to do some measuring yourself - I'll post them to you as long as you post 'em back when you're done. Can be used for internal and external measurements so you can do the pistons and bores...

Let me know mate.

Nick

[FreeFall]

I'm no expert but wouldn't the displacement be relative to bore size rather than piston size?

lol do the maths feller.

A larger piston will mean a larger bore is needed to accomodate it - so displacment goes up.

Also you can increase displacment by stroking meaning bore size is not the sole deciding factor in displacement

So my assumption stands?

You could have 85mm pistons slopping around in a bore of 87mm and the displacement would be relative to the bore and not the pistons? I have a 2.2 stroker but the bores have not been enlarged, it's all in the stroke as you say.

Not sure what math has got to do with it, apart from the formula that I posted which seems not to have anything to do with piston diameter

[ENSMR2]

The skirt was measured at 86. However that is using a ruler. I don't have fancy measuring tools like the owner of that hand does lol.

The box and the wrapping for the rings say 87 so it's got to be 87.

I hope you or your builder will be measuring them properly (with a set of verniers) before touching your block

Obviously.