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I have a 73 2002 tii ... engine bored from 89 to 91mm with molly pistons...with 360k miles on it now. Has 121 head; was cracked by the shop when pressing out the pins for a rebuild. Have a nearly brand new 1980 118 head. Clearly fits; has smaller combustion chambers. CAN I USE THIS HEAD? Have searched the new with no definitive guidance.

Thanks

Chess...

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118 casting is a 1600. No, you don't want to. Smaller ports, for starts.

with molly pistons

is that anything like mollycoddling?

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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even stranger is that molly(mahle?) dont make a +2mm oversize piston. for ANY car. and if you DO have mahle oversize, the max is +1.0mm, so if yer bore is 91mm, either that piston aint no mahle(molly?), or you got clearance problems. or, maybe there IS a piston manufacturer named molly?

Ken Inn

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  • 4 weeks later...
Guest Anonymous

Ken..appreciate the note on the 118 head.

1. Yes you are correct. THe pistons are Mahle.

2. Yes you are correct...the pistons are not 92mm as I said...nor is it the 91mm you noted. The pistons are 91.93 (the number stamped on all 4 pistons)

3. The BMW headgasket 11121316714 snugged right in. Good help from some other folks on the FAQ net.

4. The Flat head Mahle pistons complemented the 118 head ok...but just could not get enought air flow that I got with the E12 head. Some great assistance from TopEnd Performance folks that knew the 118 head and the "92mm" piston line-up.

Nice having pros on the net that have a passion to help the amateurs find a solution and get it right...and then there are those that enjoy pointing out our errors.

Best wishes.

Chess

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so any idea what the original application for the pistons was?

t

i think he has an old metric mechanic engine. the head gasket is from e30 m3, which has a stock bore of 93.4mm. so they cannot be s14 pistons, and no other bmw 4 cyl has a 92mm bore. the reason they are stamped 91.93 is because the pistons have got to be smaller than the bore(of course). mahle bmw pistons have a casting nr on the inside of the piston that tells what series they are for, and the actual piston can be tracked from that. somewhere in the back of my memory is that when jim rowe started making his big bore m10, he was using mahle air cooled pistons, i think from vw, and 92mm sounds about right. a really long shot might be a special edition e30 m3, i think for the italian market, which had a smaller displacement s14 engine, but etk no longer has this info

Ken Inn

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