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Old 02-07-2010, 12:43 AM   #1
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Default .21 Shimming

Hey guys, I recently got hold of some JP engines and see that they are shimmmed underneath the sleeve, ie. between crankcase and sleeve. Is this to increase RPM or torque. What head clearences are suited for NR engines I am running at about .7 on the coast.

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Old 02-07-2010, 02:01 AM   #2
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The real clearance can be messured by sqeezing a tip of solder between the head and piston turning it through TDC, that must be arround 0.6 to 0.7 mm

Less will give more bottom torque more will give a slight better RPM
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Old 02-07-2010, 02:46 AM   #3
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Ok, but what does the shimming under the sleeve do? Does it increase the timing and therfore increase RPM?
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Old 02-07-2010, 05:51 AM   #4
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Shims under the sleeve is a standard trick to raise the ports without grinding, I have seen it before with JP team engines.
It will give a longer opening on the intake (more fuel) and the higher exhaust will give a fraction more RPM.

When taking away the milage and bottom power should be bettered. But be sure when taking away you do need to add the same size shim extra under the head. (lowering the sleeve will lower the head and so making the head clearance smaller)
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