why do my pistons have different numbers?

[Mike-]

ive just pulled apart my 4age redtop bigport and ive got some spare 20v pistons i was going to swap into it.

i noticed that the original pistions have some different numbers stamped into them, and was wondering is this to do with them being oversized? which will make things tricky for replacing with 20v pistons

the numbers on the top of the pistons are

1,2,2,2

on the side are

3L,4L,4L,3L

all in that order with the cylinders number.

they all have a 16070 stamped on the side aswell

any ideas?

[Zak]

It's the clearances, when you buy new toyota parts you can choose the right size, eg bearings.The actual pistons should be ok, but if you do the bearings, thats the size for each cylinder. I can't remember if thats the ring size or bearing size on the piston though. There should be marks on your block too.

[Mike-]

ahh sweet, so the 1,2,2,2 numbers are all i have to worry about?

[Zak]

I'm not 100% on that, there should be numbers on the top of the block too, and maybe on the bottem as well. If you get genuine parts just write every thing down and the'll sort you out. If your getting after market stuff it's a one size fits all, so it wont matter.

[Mr Revhead]

they are different grades (sizes)
when you make 1000000 pistons and blocks, you cant guarantee you will get them all exactly the same within tolerances.
so they grade them.
also helps for blocks.... again you cant make em all exactly the same.
so by having different grades in pistons and bearings.
you can allow for differences in tolerances by mixing and matching.

[Mike-]

ok that helped a lot

ive already bought some piston rings and big end bearings from partmaster, just the one size fits all i guess, will these be fine?

[Mr Revhead]

maybe.

ALWAYS measure.

[Zak]

I should of be a bit clearer, yes, it's one size, unless you go for over size and stuff. But a tube of plastigauge is a very wise investment.

[Mr Revhead]

maybe.

ALWAYS measure.

[fivebob]

maybe.

ALWAYS measure twice.

Corrected

[Mr Revhead]

yes.

or, if your retarded like me....
measure twice
go check book again
measure again!