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Old 04-08-2007, 09:19 PM   #1
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Default how many shims to use w/ 30% OS VRZ II

Hi, how many shims do I need to use for the OS VZR II 21 on road engine. It comes w/ 0.2mm and 0.1mm, do I need to add another 0.1mm to run 30%?

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Old 04-09-2007, 11:22 AM   #2
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My understanding for a .21 Engine you would like to have head clearance of .021" - .029"

To measure use calipers to measure the distance from the engine block to the piston at TDC. Measure the Turbo Button. Subtract the two and you have your clearance.

Some people use solder and smash it between the turbo button and pistons then measure the solder.

Doug
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Old 04-09-2007, 11:32 AM   #3
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I thought the same thing till I got a Ninja. With only 0.5mm of shims the Ninja head clearance is over 0.40". It depends on the head design. The Ninja head obviously has a smaller combustion chamber than a Nova Rossi, so they have to raise the bottom of the button to keep the compression in check.

For most Nova Rossi engines flack is right........ around 0.024- 0.030" of clearance is pretty good.

For the OS I have no idea If it was designed to run on 15%-20% fuel, I'd add at least 0.2mm of shims and check for detonation after a tank or so. If it looks and runs OK leave it. If it's a dog, take one 0.1mm shim back out and see if it's better.
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Old 04-09-2007, 12:28 PM   #4
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On RB's website, they recommend adding 0.1mm shim for each 5% nitro increase. The 21 engines are factory shimmed for 25% max, so to run 30%, I add 0.1mm shim to whatever comes stock. All my nova based 21 runs great this way and they last.

Since this is my first OS onroad, I just want to make sure. I added a Nova on road 0.1 shim. They fit perfect.

FYI, the Nova shim for 12 engine will fit the OS TZ12.
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