16 replies to this topic

[Phaeton]

Just starting to rebuild a 1275 A+ MG Metro engine, the pistons have 21963 G7 N49A on them anyone any idea if they are standard? Also they are quite a dished piston, according to the engine number 12HD24 it should have a 10.5:1 compression ratio does this seem right? Or have they been changed.

Alan...

[icklemini]

a cooper piston or late MG metro type. 10.1:1 CR, 8cc dish Nominal

maybe 'standard' and some Spi'd too..

hth,
Dave

[Phaeton]

a cooper piston or late MG metro type. 10.1:1 CR, 8cc dish Nominal

maybe 'standard' and some Spi'd too..

hth,
Dave

Cheers Dave, you don't know if the G7 N49A means they are standard diameter i.e. not +20 etc.

Alan...

[icklemini]

a cooper piston or late MG metro type. 10.1:1 CR, 8cc dish Nominal

maybe 'standard' and some Spi'd too..

hth,
Dave

Cheers Dave, you don't know if the G7 N49A means they are standard diameter i.e. not +20 etc.

Alan...

no idea about the second number - probably batch/date or some such.

oversize usually has the +020 markings on them and not encrypted in code!

they are OEM pistons though so would be pretty sure they are on standard size - best get the mic out to check, can see if they are round/true as well then...

TTFN,
Dave

[Sprocket]

pistons are not round

[Phaeton]

Had a better look at the bores tonight & although at first I thought they were good, No1 has quite a step in it, the others seem okay. Going to take it into the machine shop in Worksop & let them have a look, but I think it needs a rebore & not just rings. Which is a bit of a pity but that's life, anyone any idea of the going price of a rebore & 4 pistons?

Alan....

[icklemini]

pistons are not round

Indeed. well done.

anyone any idea of the going price of a rebore & 4 pistons

Rebore from £70 ish - pistons, well depends which ones you go for... £60 for $hitters 21251s, £150 for 21253's for example

[Phaeton]

£60 for $hitters 21251s, £150 for 21253's for example

Sorry for being thick long time since I've been inside an engine, what's the difference between the two?

Alan...

[icklemini]

quite a bit of diference in the quality and design areas.

the 21251 are ok for low revs low compression use, or short life in a high compresion, high revs application.
They are a low compression piston 8:1 in standard guise... (blocks that have used these pistons ususally have a chunk taken off the top to get the CR back up)

there is a 21250 piston that is a better quality material having the same design with a wide ring configuration the same as the 21251

they have a massive oil groove in them.

The 21253 is a good quality piston with a competely diffent thinner ring pack for higher performance use.
The oil slot on the 53's also doesnt go 80% around the piston as it does on the 50,51's

so the 53 is the 'daddy' of the 2125x pistons... they are high compression as standard.

humbers will be on the underside of the piston - but you can notice them (the 21251) straight off with the oil groove being so big!

hth,
Dave

[Phaeton]

Are these the cheap & nasty ones, or a reasonable choice?

https://www.plminish...p...STON&page=1

Alan...

[stevesmini]

id get some powermax with stainless steel rings run in on thick cheap oil to bed rings in or go for cooper pistons as they are solid skirts with oil holes rather then slots

[icklemini]

Are these the cheap & nasty ones, or a reasonable choice?

https://www.plminish...p...STON&page=1

yep they are the 21253 (judging by the product code!)

ttfn,
Dave

[TOMMO0302]

quite a bit of diference in the quality and design areas.

the 21251 are ok for low revs low compression use, or short life in a high compresion, high revs application.
They are a low compression piston 8:1 in standard guise... (blocks that have used these pistons ususally have a chunk taken off the top to get the CR back up)

there is a 21250 piston that is a better quality material having the same design with a wide ring configuration the same as the 21251

they have a massive oil groove in them.

The 21253 is a good quality piston with a competely diffent thinner ring pack for higher performance use.
The oil slot on the 53's also doesnt go 80% around the piston as it does on the 50,51's

so the 53 is the 'daddy' of the 2125x pistons... they are high compression as standard.

humbers will be on the underside of the piston - but you can notice them (the 21251) straight off with the oil groove being so big!

hth,
Dave

Is the 21253 representing a certain standard regardless of the manufacturer? Or is it a part number that only applies to a certain brand?

[icklemini]

AE produce the 21253 piston...

other manufacturers may have their own numbering that cross-matches to a 2125x piston..

[Jordie]

Shop around for the rebore. I had mine done +0.60" for £50 + vat