piano top pistons ok to use with 121 head?

[repoman]

Doing some research on the FAQ, and it appears that the 121 head should be used with the bathtub pistons. I just got my son's 121 head back from the shop and realized that the pistons are the piano top. The block is from a 1976 and the head is a 121 date stamped 74. The car is a 1973. Just wondering if using the piano piston are ok with the 121 head. TIA

[mac]

Nope. Not without some modifications. Either to the pistons or the head.

Are Piano Top pistons already in the block?

Sell the 121 head.

Buy an E12 head-----re-install.

mac.

[repoman]

Nope. Not without some modifications. Either to the pistons or the head.

Are Piano Top pistons already in the block?

Yes, pistons already installed. How can I tell if any of the previous owners modified the head to use the piano top pistons? I can post some pics of the rebuilt 121 head that we just got back from the shop yesterday, if that would help. It does not appear that any mods were done to the pistons.

[FB73tii]

Did this engine previously run with the pistons and head you have been describing? Based on piston dome shape and combustion chamber shape it just wouldn't work unless modified as posted above. But then one would end up with a strange shape to the combustion chamber and squish and likely non-optimal combustion (less power). Can't understand why anyone would do that.

If you have not already, check out the FAQ's piston and head database. You have to scroll down pretty far for the photos of the heads:

Cylinder head CCs volumes, pistons, block and CR

by Pat Allen

http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/t,313512/

Fred '74tii & '69GT3

[mac]

Post some pics of the combustion chambers in the 121 head. We'll be able to figure it out.

Some pics of the top of the pistons too? .........

mac.

[repoman]

Did this engine previously run with the pistons and head you have been describing? Based on piston dome shape and combustion chamber shape it just wouldn't work unless modified as posted above. But then one would end up with a strange shape to the combustion chamber and squish and likely non-optimal combustion (less power). Can't understand why anyone would do that.

If you have not already, check out the FAQ's piston and head database. You have to scroll down pretty far for the photos of the heads:

Cylinder head CCs volumes, pistons, block and CR

by Pat Allen

http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/t,313512/

Fred '74tii & '69GT3

Don't know for sure, as the head was in the trunk of the car. Previous owner was not sure what was wrong with the head, supposedly, he removed it.

Yes, I did check out the head/piston database. It was my recollection, from years past, that the block and head may not work, however, the database did not state that the two would not work, thus my initial inquiry......

[Mikesmalaga72]

I would change either the pistons to the bathtub type like on IE site or NOS, or get an E 12 head one or the other.

Good luck

[repoman]

Post some pics of the combustion chambers in the 121 head. We'll be able to figure it out.

Some pics of the top of the pistons too? .........

mac.

Enjoy! It appears that the head has not been modified, based on the cylinder shape. No way that piano is fitting into that bathtub! Does everyone agree? Thanks for all the assistance on this.

Good news is that I have a lead on a rebuilt E12 head. Anyone here in the market for a rebuilt 121 head for $450 plus shipping??????

[mac]

Post that rebuilt head in the For Sale section.

For $450+, ready to go, bolt it on,.....somebody in need would be a fool not to grab it.

mac.

[stone02]

Hi,

it was a long time ago that i had this same

situation. so the engine shop instructed me to

rest the head on the motor without the gasket.

then mark the conflict area between the pistons

and the head. i did it with carbon paper.

(if you don't know you are younger than 30.)

then us a dremel or a grinder tool to remove

the conflict area. So, when i did it the actual

area in each head hole was not very big,less

than the size of a chocolate chip. then retest

until the motor does not hit the head. when

you reassemble the motor with the gasket in

place the thickness of the additional gasket

makes sure that after thermal expansion the

parts will not hit.

Finally when i ran the motor, it was a rebuild,

it was fine.

good luck

stone

[TobyB]

This will work.

But the pistons and the head work together to maximize flow, optimize

squish, and feed Bavarian squirrels-

if you can get an E12 head for those pistons, it's a better option.

Or 121 pistons.... since I've never pulled a used piston out of a block

that I found to be worth reusing...

t

[dp]

On 1/9/2013 at 3:00 PM, TobyB said:

I've never pulled a used piston out of a block that I found to be worth reusing...

 

Had to remind myself 

[echappe]

My 71 came with Piano tops and a 121 head. I believe there 2 types of piano tops. One with a much lower profile and one with a much higher profile

[Lorin]

I have done this in the past, in a pinch. Find where the piston crown interferes with the head and remove that material.

It's not ideal as others have mentioned but it never caused a problem for me. 

 

Try to maintain at least 1mm of gap between any part of the head to the piston.

[Djthom]

I recently purchased a 73tii and pulled the head today.  I was very surprised to see it had  121 head with Piano top pistons.   Doesn't look like any modifications have been done.  The engine block, injection pump and plenum are from a 74 so this can't be the original head.  I dont see any signs of conflict 

 

Maybe as echappe suggested above there were 2 types of Piano top pistons?

 

I have the original engine to rebuild but need this one to last me a bit longer. S