I just had a look in the parts book for the E10 Cherry,wich came with A10 and A12 engines.The A10 pistons were 12010-18021 till 05/72,then 12010-H2301.The A12 piston was 12010-H1011.It seems that they first used the B10 piston,then for some reason the number was changed.No idea if there was a change on the piston itself,I never had the opportunity to open a B10 engine and compare.As Dodgeman said the dimensions are identical,and it is an easy swap to gain some compression on an A12.Datsun SSS,are these the pistons from that rallycross engine and are they standard bore?Any pics and info on the rest of that engine?I am still interested to learn more about it as that car was prepared here in Belgium.I haven't found any info about it yet,but I keep asking around.....

This is a link to a related thread.

So, what do we have here. The standard garden variety A10 piston serves double duty as the high compression, flat top 1200 GX piston, straight out of the factory.
Is that correct?

Quote:Not the GX "high gas" pistons:

Part numbers:
12010-18021 PISTON SET-with pin (standard size) (High Gas) GX-H B110
12010-18021 PISTON SET, with piston pin (standard size) ALL B10

18021 is the third part number for B10 pistons.

The part number for A10 pistons is the same for the two different engines. [Coupe & Non Coupe] It's the cylinder heads that vary with one number for the Coupe & another for Non Coupe, so this must be where the extra half point of compression comes from.

Dimentionally, A10 & 1200 pistons are interchangeable, however the 1200 ones have a dish. With the extra 11mm of stroke the compression went up too much, so a dish was included to bring it down to the same as the KB10 engine.

Using flat top A10 pistons will restore the compression that was lost by the inclusion of the dish, but, depending on the source of the pistons [genuine or replacement], just be sure that there is no problem with the skirt to crankshaft clearance. I think that genuine pistons have a longer skirt.

A10's do have flat top pistons. What is the bore difference from a A10 to a A12GX? Is it only the stoke that increased the capasity to 1.2ltr? Is it possilble they are the same piston... probably not but you never know!

Part Numbers:

12010-H1001 PISTON SET-with pin (standard size) (Reg Gas) ALL (exc. GX-H)
12010-18021 PISTON SET-with pin (standard size) (High Gas) GX-H

Interesting. The GX-H part number looks like a Datsun 1000 part number. Is it the same as the high-compression KB10? KB10s didn't have dual-carbs, did they?

Regarding GX, it uses same rings, rods, crankshaft and flywheel as standard A12. In the block, apparently only the camshaft is different (and for some GX, the pistons are different).

That's interesting as I had always believed that the GX came with flat top pistons, but my parts book does not list them at all.
Both the 1200 GX & the 120Y gx engines that I have dismantled had dished pistons.

The part numbers for pistons simply have the A12 code in the "application" column, but no reference to GX whatsoever.

Standard pistons are dished. GX engines came both ways.

whats the diferences between the flat top pistons and the standard pistons in the a12 gx?

my gx have flat top ones.