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Old 11-23-2008, 07:32 PM   #1
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Default engine shimming

Anyone know where i can find some info on engine shimming? I learned something important this weekend at "the big race", never remove a head shim when u dont know what your doing and why your doing it.

So any information will be great

thanks
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Old 11-23-2008, 07:40 PM   #2
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Try to always use # shims that came stock. For a .21 motor most motors are good for 30% with around .026 piston to head clearance. Put the motor at tdc (piston at top) remove the head, measure down to the top of the piston, subtract the measurement of the head button down to the shims.

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Old 11-23-2008, 07:56 PM   #3
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Most .21s are shimmed from 22 to 28 max, you can change the feel of the motor a bit by adding or removing them, maybe you where trying tjhis and it just didn't work, when you go below factory shimming it can produce great results, and it can be adjusted by button work as well, but they key is the lower the squish the cooler plug you need.
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Old 11-24-2008, 07:10 AM   #4
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Here is an article that explains how nitro %, glow plug selection, and shims affect timing: http://www.ronlund.com/shim.htm

In this thread I described how to determine squish height by nitro percentage:
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Old 11-24-2008, 08:23 AM   #5
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Thank you guys for all your help
i bought the motor (821b) used and took it apart for inspection, upon doing so i noticed it had two thick silver shims and 1 copper so i thought it was too much and took out a silver one (boy was that a big mistake) we couldnt get this thing tuned to save our life. Then a great guy from the LOSI team came by our pit area and checked it out and said the squish was'nt right, so after we got it corrected it ran like a champ, that is until i went and changed fuels
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