What piston might this be?

[Healey3000]

Hi,

 

Any ideas on what this piston is?  Looks like a cast piston but I can't figure out what the compression ratio is.

 

Thanks!

[Tommy]

It's the grand piano style for e12 head. From this angle it's a bit hard to tell the CR. You should measure the dome height. To me it looks like 9,5:1 tii piston.

 

BTW. Does anyone know if the great faq piston guide can still be found somewhere?

Edited September 18, 2019 by Tommy

[PaulTWinterton]

Walloth and Nesch sell a Mahle 89.47 for 9.5cr  Yours looks to be 89.97.  Could be 10.0cr?

 

https://www.wallothnesch.com/en/catalogsearch/result/?order=name&dir=asc&q=2002+piston

[Tommy]

Yes, they seem to be 1mm oversize. A mm makes a difference of about 0.2 in CR, not much. That is assuming the dome is exactly the same.

[coloincaalpine RIP 2021]

Those look like the 10:1 E12 pistons.

[02Les]

9 hours ago, Tommy said:

 

BTW. Does anyone know if the great faq piston guide can still be found somewhere?

 

I had this one stashed away. HTH.

OEM Pistons Guide.doc

[mac]

Second oversize, MAHLE, 9.5:1 c/r, for BMW E12 head.

 

(some folks refer to them as "grand piano" stye.)

 

Mac.

[Healey3000]

Hi,

 

Thanks for all the insight, particularly that table, 02Les.  However, this raises more questions.  The table does not list an 89.97 mm piston so does that mean I'm on thin ice if I bore out that large?

 

Mac, wouldn't a 1 mm oversize mean a "fourth" oversize, since each oversize is 0.25 mm?

 

A 10:1 CR does not exist for an e12 head - correct?  If so, these must be 9.5 or less.  Could they be 9:1, given that "0900" on the piston?  I hope not.

 

 

[PaulTWinterton]

2 hours ago, Healey3000 said:

The table does not list an 89.97 mm piston

 

I would shoot W&N an email to get the final answer.  They are very quick to respond.

[mac]

MAHLE tells me:  ORIGINALLY(back in the day) they made third oversize @89.97mm.  Later on, for one reason or another, They changed third oversize to 90.015mm.  They never made a fourth oversize.  

 

That's their story and they are stickin' to it.  

 

Mac. 

 

PS.  You are correct re:  10:1,  E12 pistons.  MAHLE never made 'em. 

[Healey3000]

22 minutes ago, PaulTWinterton said:

 

I would shoot W&N an email to get the final answer.  They are very quick to respond.

I did.  They said we don't sell an 89.97 and we have no idea who makes it

[jgerock]

89.97 Mahle pistons I have in my 72tii engine.  Pistons were sourced from 2002Haus.

Edited September 19, 2019 by jgerock

[jgerock]

https://www.bmw2002faq.com/forums/topic/108895-piston-markings-what-they-tell-you/

[Jeff]

Here are some NOS BMW E12 head 89.5 9:3 compression pistons.

[visionaut]

Here’s two pics of a used Mahle 2nd-oversize (89.47) 9.5:1 ‘grand piano’ for the E12 cylinder head. Note the markings and locations are a bit different than Healey’s, making me suspect his piston might not be Mahle.

 

I ran the above prior to my last rebuild, where I went to the 89.97 version of the exact same Mahle 9.5:1 grand piano, which I sourced through IE back then (2006). It was cited as being 4th oversize (1.0 mm larger than stock).

 

Jim’s pistons posted above are also 4th oversize, but look to be the 10:1 dome profile, for the 121 head.

 

Tom