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HomeAircraftHelicopterHelicopter Main Discussion › What do u use the shims for in the OS 90 Hyper?
02-09-2008 06:50 AM  10 years agoPost 1
FenderBean

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Fort Hood TX

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is it to give more or less compression , or is it for diff types of fuel? just wondering

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02-09-2008 06:57 AM  10 years agoPost 2
f14tomcatfreak

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rochester,ny us

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both

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02-09-2008 06:59 AM  10 years agoPost 3
FenderBean

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Fort Hood TX

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okay so I dont really need them. Just wanted to expand knowledge alittle

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02-09-2008 12:22 PM  10 years agoPost 4
busyflyin

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Owosso, MI USA

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.90 size engines are known for high compression which means difficult starting. Headshims can be used to lower the compression and easier starting. I'm not sure about the fuel side of it. I have run both 15 and 30% in mine and like the 30% better.

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02-09-2008 02:08 PM  10 years agoPost 5
FenderBean

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Fort Hood TX

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yeah i have a YS 90 and I have to use my portable car starter LOL

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02-10-2008 01:02 AM  10 years agoPost 6
busyflyin

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Owosso, MI USA

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What i have found that works well is to cut the "L" off a 6mm allen wrench, chuck it up in my 24 volt drill, and run it around for 5-10 seconds. That loosens it up enough to use my starter.

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02-10-2008 01:24 AM  10 years agoPost 7
patriot21

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Byron,MN

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I use 1 shim... seems to be a nice balance of easy starting and smooth running

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02-10-2008 01:25 AM  10 years agoPost 8
Yug

rrMaster

UK. Herts

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Important thing to remember about head shims is they allow you to time the ignition by way of compression so you can avoid early detonation. It's a shame the standard shims are either 4 or 8 though, 'twould be nice to have a 2

Vegetable rights and Peace

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