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I own a carbed '78 m10b16 E21, I'm going to rebuild the engine next month so I started collecting parts and I found a 121 head in great condition (really great, looks brand new) for cheap, so I started evaluating something more than just a rebuild.
Do I just need to rebore the block to 89mm and buy pistons to make it work?
I noticed that head has a lower chamber height than mine, which pistons should I buy?
Thanks in advance!
"Averroės, Kant, Socrates, Newton, Voltaire, could any of them have believed it possible that in the twentieth century the scourge of cities, the poisoner of lungs, the mass murderer and idol of millions would be a metal receptacle on wheels, and that people would actually prefer being crushed to death inside it during frantic weekend exoduses instead of staying, safe and sound, at home?"
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Hallo, I dont think it would be so simple. Difference between your 1.6 and a 1.8 engine is as you wrote the bore. First: to bore it to 89mm it needs 5mm of material to take off and i dont know the 1.6 block to have that much material. Second: If it works to bore it so much you will need a custom made piston to work with your 121 head which was only used for 2.0 ltr engines. 1.6 and 1.8 got the same stroke and another bore. 1.8 and 2.0 got the same bore but different stroke. There is no stock piston to use with a combination of a 1.8 ltr bottom and a 121 head. Andreas
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Seeing the head gaskets everything seems the same, the 5mm are added inside the bore, so I guess the block is the same just drilled with different diameters, see attached pictures. [pic.1 is m10b16, pic.2 is m10b20]Originally Posted by E21M10
Regard point 2 you are right, I have 71mm stroke instead of 80, the rods have the same component number so I guess the crankshaft is different, would I need to replace it with a m10b20 one?
Thank for the time!
Last edited by johnharrison; 05-23-2018 at 01:23 PM.
"Averroės, Kant, Socrates, Newton, Voltaire, could any of them have believed it possible that in the twentieth century the scourge of cities, the poisoner of lungs, the mass murderer and idol of millions would be a metal receptacle on wheels, and that people would actually prefer being crushed to death inside it during frantic weekend exoduses instead of staying, safe and sound, at home?"
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As i wrote you will need for your combination special made pistons. Rods for 1.8 and 2.0 engines are the same. The crankshaft and pistons make the difference for the raised stroke. To solve your problem use a 2.0 bottom with the right pistons for your 121 head. Another way is using your 1.6 block bored out to 89mm, but here is guessing not the right way be sure before doing this, with a 318i head from an E30 engine. Big ports, big valves and a good flowing head and possible to use stock pistons from late e21 1.8 carbed or e30 1.8 318i. E21 heads are second choice because you will have to plug the injector holes in the head. I am running this in my 316 but it is a 81“ with a 1.8 engine for stock.
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I'm going to check with IE, I'd like to keep the 1.6/1.8 bottom end because of the lighter cranck plus I don't want to touch transmission and clutch being them perfect.
I still have doubts about the head, probably the 118 gonna have better combustion but the 121 still has bigger ports and the one I have is ready to go, my cranck has 4.5mm less half stroke than the 80mm if I'm right, so the custom pistons are going to be just taller, using a 4.4mm domed 89mm piston isn't the same? Plus I read on the 2002 forum that it's possible to use a 121 head on a 1802, didn't the 1802 have our bottom end with 89 bore?
"Averroės, Kant, Socrates, Newton, Voltaire, could any of them have believed it possible that in the twentieth century the scourge of cities, the poisoner of lungs, the mass murderer and idol of millions would be a metal receptacle on wheels, and that people would actually prefer being crushed to death inside it during frantic weekend exoduses instead of staying, safe and sound, at home?"
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Things are getting comlicated from that point. If you are shure to bore out to 89mm this will put a lot of temperatur and mechanical stress at it. It will be absolutly nessacary to use a torque plate and install the main caps. Let it stand for 24h after rebore before you go any step further. Dont“t know what head would be the better one. Flowrate differences are marginal in my opinion. Both pistons are same hight overall. The difference is the location of the wrist pin hole in the skirt. 1.8ltr. blocks in 02, E21 and e30 all use the same bore / stroke. I only know early Neue Klasse 1.8ltr. blocks to use a different bore / stroke ratio.
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Yeah I noticed the intake is different size but I'm using a manifold with a 36/36 weber I found from a 2002.
I got the head, as you can see in pictures the chamber extrudes only partially on the little passage behind the valves so I'm trying to put it on the 84mm bore with 2L head gasket, visually there should not be any clearance issue but I have to wait for the pistons to do a proper clay test; the pistons I bought are as the one in the third picture.
"Averroės, Kant, Socrates, Newton, Voltaire, could any of them have believed it possible that in the twentieth century the scourge of cities, the poisoner of lungs, the mass murderer and idol of millions would be a metal receptacle on wheels, and that people would actually prefer being crushed to death inside it during frantic weekend exoduses instead of staying, safe and sound, at home?"
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