What's the difference between U.S and EURO spec pistons.

[Dave H]

Is it the compression ratio ? Does one have a domed top  or something ?
Here's my problem..my car has a 280 se euro engine fitted .I say it's euro
Only because the engine came out of a UK car.
The motor is being rebuilt... The bores are worn and require rebore
From 87.00 to 87.50 which I believe is the last size.
New pistons from Europe are around Eur 1500 but I've
Seen some Mahle OEM 2nd oversize 87.50mm part no
1300309117 for EUR 600 !
These I thought would be perfect until someone said " they are U.S
Spec !!! " kindly help me out here .. What is the difference ?
Thanks as ever you guys !

New

[Dave H]

I cant understand why this part number of 1300309117 only appears in the Mercedes EPC for U.S spec cars and not Euro.
My cylinder head casting number 130.016.1101 is for a late 280 head, with the oval type head gasket .
If the block was re-bored to the correct size, all things being equal ,why would they not fit ?
I agree i am being led by the price, i would buy them in a heartbeat if i was sure they would fit as i am re-boreing to 87.50mm anyway.
SLS in Germany dont know what these fit only that they are for a U.S spec 280 ! Why would they not fit in any late 280 ?

[Raymond]

I've never heard of any European vs. US specification difference in the pistions, only the camshaft.  There surely won't be any difference in the holes.  For 900 Euros difference, no one will know once the head is bolted on. 

[Dave H]

Got to the bottom of it....it seemed to good to be true.
The U.S spec 1300309117 pistons do not have the cut out for the v/vs on the top !
They are slightly shorter as a result ie length 79.9mm v/s 80.6mm and have compression height of only 47.9mm v/s 48.6mm for the EURO spec pistons.
Phew! im starting to bore myself...
All said and done the EURO ones are a bit more manly ! gurrr.
Being a bit taller they must be higher compression...only guessing.
Sad thing is i found them cheap for around $134 each and another site for $102 !
The 1300309717 or 1300300018 ones i need are much more expensive so the quest goes on....
Daft thing is i bet they do fit and its what some of you guys have in your late 280sl cars....
If you live in the U.S do your pistons have the flat cut out on the top to avoid the valves ?..... i wonder ....!
 

[Cees Klumper]

Joe Alexander (and I) rebuilt my engine with US spec pistons. I drive the car in Europe, and it goes pretty darn fast (I've nudged 120 MPH several times). So I'd say: go for the US spec pistons, keep the cash in your pocket and don't worry about a thing.

[Dave H]

Thats what i am thinking ,unless somebody knows of a reason not too.
They are slightly shorter because they do not have the step on the top! is that it ?
Theres bound to be a catch but until somebody points it out !!!!
Tell me Cees ,was your engine Euro spec and are these indeed the pistons you fitted ?
Also check out the diagrams on    www.autopartoo.com
put in the numbers on their parts search and the sizes and drawings come up.
This is the U.S spec piston 1300309117 without the step on top .

[Bonnyboy]

My two bits...

I'm far from being considered even remotely intelligent in this topic but ....    We don't have hemispherical combustion chambers so it may not make a real big difference.  A stepped top piston may need to be a stronger piston to withstand the extra forces hence extra $$ but 1/2 of 1 mm doesn't seem like alot even at 4,000 rpm.   The flat top may just work better with lower octane fuels and ur fuels are much better than they were 40 years ago so based on that its a plus.  And being lighter than a stepped top may negate some of the loss of oomph.  I would say going from a stepped piston down to a flat top piston would actually lessen the strain on the engine.   

However I have no actual experience - results may vary - I offer no warranties

I would do it if I needed to.   

[Dave H]

I guess I'm just waiting for the rubber stamp off the Benz Dr or
Stickandrudderman....I don't think I would go it alone without
The approval of those guys..I just tinker about in the garage.
Those guys do it for real..
Come on  you guys... Where are you when I need you !

[Benz Dr.]

The step piston doesn't produce as much compression as a flat one will. The high side on the piston will be about evn with the top of the block - the lower side has nothing to do with valve clearance.
I just installed a set of pistons in a '69 290SL and they were flat toped. They also had USA stamped onn the top and one thing I did notice was that there was a small groove below the top ring with nothing in it. This is not a groove for a piston ring as the sides of the groove are somewhat angled. The oil scraper ring and oil control rings are below this empty groove.
I've also found that replacement pistons are a bit shorter than original pistons so that you can deck the top of the block without getting it too low. In most cases you would need to remove about .50 mm from the block to get some amount of piston crown height out of the block. Left at stock dimensions, the pistons will often be at, or slightly below the parting surface, which results in lower compression numbers. If you want 175 PSI the pistons would need to stick out of the top of the block. Refer to the BBB for exact amounts.   

[Dave H]

Thanks as always Dan...
I've managed to find a really good machine shop to do the
Rebore work as the cylinders do have a good ridge on them.
Also to do the v/v seats in the way that you mentioned and polish
The crank, deck head if req and crack check etc.The guy even does
White metal work so I was impressed.
Hopefully the polish and matchbore will negate any slight loss
Of  compression however Cees used the USA pistons and his goes
Like the clappers he said.
Thanks again to all you guys and I will post lots of pictures as the
Work takes place.

[Benz Dr.]

Flat top pistons are standard compression. The stepped ones are lower. I don't think this is a USA versus euro consideration and is more like what's available. I know the third version 230SL pistons only only come in stepped at this time.

Early and intermeadiate 230SL, if you canget them are only flat top. 250 are all flat top while some 280SL pistons are stepped. 

Never remove anything more than absolutley needed as far as the cylinder head is concerned. Good used blocks will be available for a long time to come but good used heads won't be.