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K1300GT K1200LT
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Discussion Starter · #1 ·
I'm sending a LT piston to a piston manufacture for a quote on having forged pistons made. There is a spec A & B piston depending on the finished bore size. I'm looking for the minimum finished bore size. I'm not looking for the 70.5 mm or 2.770" bore size but the actual min. size.

I'm also planning on having the compression reduced to 9.0 to 1 & I need to figure out the cc volume of the piston needed. That's why I also need to know what the head cc volume is.

Thanks, Dave
 

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I do not know the compression ratio, but the K1200 RS (and maybe GT) pistons were forged, where the LT ones were cast.

Measuring the combustion chamber volume is normally done by clamping a piece of clear plastic to the head, with a small hole near a top edge of the chamber with the head tilted up, then filling the chamber with liquid, measuring the volume used.
 

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K1300GT K1200LT
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Discussion Starter · #3 ·
Thanks David, I have a head I could measure the cc's on but I don't have a burette or a plastic piece to clamp on the head. I'll get both if I have to but I was hoping someone would have a CC #.
 

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dshealey said:
I do not know the compression ratio, but the K1200 RS (and maybe GT) pistons were forged, where the LT ones were cast.
I have a '99 RS here and the pistons are cast. I have bought both pre and post '05 pistons in the last 3 years and all have been cast. If any were forged pistons it is now a thing of the past. The part numbers show the same for early Rs, GT and post '04 LT. Only the pre '05 LT (lower compression) pistons are different but still cast. A forged piston would be a benefit for long term reliability of this engine.
 

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K1300GT K1200LT
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Discussion Starter · #5 ·
A big thanks to my parts guy John at BMW Motorcycles of Charlotte. The min. bore size is 70.466 mm. I can cc the BMW piston dish to get the other numbers I need. I'm hoping I can reduce the compression in part by making the valve pockets deeper & making it a non interference engine.
 
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