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ok, is my friend an idiot?

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My friend has an 02 cr250r. he just milled 27 thousanths off his head. That seems like way to much to me but I am a four stroke guy. any ideas?

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If his compression is too high the piston can be reliefed to drop the ratio. He also could buy thicker gasket or even double them up to lower the ratio aswell.A shorter rod is also another option if needed. He could order a piston with a short pin to top distance, but this would be a custom piece.

For those not familiar with thousands in the real world, he milled approx 5 or 6 sheets of paper thickness off his head.

I would assemble it and roll it slowly to check the clearance then decide which way I wanted to correct it if needed.

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The squish clearances I've measured on CR's were between 0.065" and 0.080" in stock form. I took 0.025" off my '01 head and ended up at 0.037" with a Wiseco piston. After removing 0.025", he's probably near the edge and should carefully measure his current squish clearance using some solder and a micrometer. According to what I've read, you need to be careful when setting the squish clearance at less than 0.040"; rod stretch at high RPM can let the piston hit the head (I'll be pulling the head to check for that soon). My engineering partner sets the squish clearance to 0.030" in his 10,000 RPM 5.8 liter mustang and ends up with signs of very light piston/head contact.

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