11 replies to this topic

[Brams96]

I've seen an add for some Cooper S pistons and my question is does this sound like these pistons are 1275 +60th 8cc dished?

"One set of new old stock four ring plus .060 /1.524mm dished pistons suitable for cooper S or 1300 A series engines MG etc"

What would be a good price to pay if they are new old stock??

Edited by Brams96, 22 April 2009 - 06:28 AM.

[Guess-Works.com]

not a lot as you can get better pistons, ie 21253's for about £35 each...

[MRA]

21253 are a much more modern and a better product, so the only reason for buying genuine old stock is to ....... urm ..... urr umm ..... oh yeah for someone who wants to build an engine for their cooper S and wants to use genuine parts...... but then nobody will see them so whats the point.

[Sprocket]

Dont know what you all mean. I'm running Cooper S pistons in my 16 valver to 8000rpm. They are far from a crap piston, infact are a better piston than the 21253.

HOWEVER!!! there are Cooper S pistons and Cooper S pistons. There are four ring pistons that are far from performance items, that have a huge oil drain slot. The pistons I use are the 19320 three ring veriety with oil drain holes, not the slots. and considered a very good piston. I have no complaints anyway and the engine has been buzzed to 8k regulary.

Like I said, there are Cooper S pistons and Cooper S pistons

The ad sounds suspicious to me. I do not think they are Cooper S pistons. The hook line 'suitable for Cooper S' doesnt mean they are Cooper S pistons Without a part number they could be anything

[MRA]

I guess we all have our different views on this then

[62S]

Assuming you mean these

eBay of course

Being Hepolite thay are a good quality piston but despite what the description claims, these are not Cooper S pistons they are 8.8:1 comp ratio from Mini 1275GT, some Austin 1300, Sprite/Midget, Allegro 1300 - modern equivalent is 21251.

[Brams96]

62S - Yes those are the ones I'm looking at. Am I correct in assuming these are 1275 +0.060 which would give a final engine size of 1330cc?? or have I got that wrong? Would the compression ratio still be 8.8:1? Are they worth spending the money on or should I go with something like THESE.
I found THIS interesting site with different piston size.

[pothole]

Thanks for that great site you linked to, so much information on there.

pothole

[Cooperman]

Best bet is to buy a new set of Hepolite 21253 from one of the Mini parts specialists. You will be looking at around £140 for the set if you do a 'deal'. The 21253 is a modern low-drag slipper piston, very durable and strong.
The best piston I have ever used is the Karl Schmitt, the quality of which is amazing, as is the strength. It's what I have in my rally 1330 'S'. The last set I bought, about 3 years ago, cost me £400+ for the set, but they are worth it for competition.
However, for value you can't best the 21253. The early Cooper 'S' pistons were heavier, although still a good pistons. With older stock the quality control was not so good and balancing is vitasl for a high revs engine, whereas the 21253 is very accurately machined and they all weigh the same out of the box.

[MRA]

Best bet is to buy a new set of Hepolite 21253 from one of the Mini parts specialists. You will be looking at around £140 for the set if you do a 'deal'. The 21253 is a modern low-drag slipper piston, very durable and strong.
The best piston I have ever used is the Karl Schmitt, the quality of which is amazing, as is the strength. It's what I have in my rally 1330 'S'. The last set I bought, about 3 years ago, cost me £400+ for the set, but they are worth it for competition.
However, for value you can't best the 21253. The early Cooper 'S' pistons were heavier, although still a good pistons. With older stock the quality control was not so good and balancing is vitasl for a high revs engine, whereas the 21253 is very accurately machined and they all weigh the same out of the box.

Exactly

[Sprocket]

the 21253 is very accurately machined and they all weigh the same out of the box.

No they dont. I bought a set and had to take two back as they were 3 grams different between I had the same thing with a set of OE pistons. Maybe im just unlucky

[MRA]

Almost exactly then

However I bet you would be hard placed to find a set of "old" cooper S pistons with that accuracy.... all I am saying is that these pistons have been around a while, there will be deficiencies within the metal (mainly the alluminium) .....

I know your Mini is not being built to "fly" (as in like a bird) but if this was an aircraft, the older pistons would have to be scrapped or at least fully inspected (xray'd etc) for defects before they could be used, simply because faults within the piston could cause failure within your engine......... reliability extra cost associated with a rebuild would make these "cheap" pistons extremely expensive and not worth the money or cudos of having "cooper S" pistons in your engine..... even more so as they are not cooper S pistons anyway

Edited by mra-minis.co.uk, 25 April 2009 - 06:31 AM.