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02-24-2010 12:11 AM  10 years ago
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NQNA

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USA

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O.S. .91HZ Shims
Posted this on the Trex 700 area..

Planning on running my O.S. 91HZ in a Trex 700 on CY 30% with a SB-20 Hatori.

Should I run the extra head shim provided by O.S.?

Thanks..
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02-24-2010 12:16 AM  10 years ago
Dr.Ben

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Richmond, VA, USA

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Yes, and it may want an extra 0.004" after that.

Ben Minor
Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA
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02-24-2010 04:18 AM  10 years ago
outhouse

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auburn ca

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would this be the same as 2 head gaskets?
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02-24-2010 05:00 AM  10 years ago
Dr.Ben

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Richmond, VA, USA

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What you're calling the head gasket is an 0.008" shim. You can increase the shim from there in either 0.004" or 0.008" increments.

Ben Minor
Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA
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03-12-2010 10:38 PM  10 years ago
Thumpernator

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Senoia, Georgia, USA

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I can not find shims in the .004 size. Anyone know who carries them?

Dr Ben, are you saying that a total of .020 in shims may be required?
Dave
I keep on thinking, but nothing's happening. Knuk, Knuk, Knuk
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03-12-2010 10:56 PM  10 years ago
DS 8717

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Mine came with the .004"/.1mm shim installed in mine,and an extra shim that is .008"/.2mm.I guess they set it up for 15% nitro with the thinner shim.I am using Curtis 30% in mine and it has never run right and now i see why.YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED
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03-13-2010 01:23 AM  10 years ago
outhouse

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auburn ca

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I had the 1 shim and ordered the 91sz kit that has both shims your talking about and i added both and it runs great and no tuning issues at all with rapicon %30
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03-13-2010 03:13 AM  10 years ago
DS 8717

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so your using .012" total.mine only had .04" in it from the factoryYOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED
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03-13-2010 03:15 AM  10 years ago
THX1138

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Indianapolis, IN

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I am using both .004 and .008 shims on my HZ with an Mp6 and Magnum 30% Heli plus. Runs like a champ in Indianapolis. I am not the best at tuning engines and I have mine singing, it totally came right in after a few break in flights. Pulls like a champ.

Lou
Just give me five dudes and two flashbangs...
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03-13-2010 04:14 AM  10 years ago
TMoore

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Cookeville, TN

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I've got an Align 91HZ in my TD3 with the stock head shim, 30% Magnum and a Funtech X90 muffler. Runs great.

TM
Part 107.
The only ZERO flight hour certificate in the world.
It's like getting a driver's license without the driver's test.
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03-13-2010 11:16 AM  10 years ago
DS 8717

rrProfessor

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I am using both .004 and .008 shims on my HZ with an Mp6 and Magnum 30% Heli plus. Runs like a champ in Indianapolis. I am not the best at tuning engines and I have mine singing, it totally came right in after a few break in flights. Pulls like a champ.

Lou
Thats the same muffler i am using,with the .04" shim mine was rough running even with the mixture rich. My YS 91SR is much smoother runing and has more power,but has the SB19 muffler on it.I have a SB20 for the OS i will try after i get it broke in and see what the difference is between the MP6 and SB20.

I dont want my piston looking like this

YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED
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03-13-2010 06:46 PM  10 years ago
reiserrob2003

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Brockton, MA.

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Is there any noticeable loss in power with the shimming, seems logical with the reduction in compression ratio.
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03-13-2010 10:25 PM  10 years ago
outhouse

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auburn ca

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your not taking enough compession away to make much of a power difference.

with 1 shim a common complaint with %30 is that there is a fine edge between slobbering rich and to lean.

i added the 3 shims and tuning is easy and ive noticed more power with %30 and 3 shims over %20 and the 1 stock shim.
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03-13-2010 10:55 PM  10 years ago
DS 8717

rrProfessor

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If the compression is TOO high it will make less power than the right compresion. It will run hotter and the needles will be very sensative to adjust.YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED
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03-14-2010 06:52 AM  10 years ago
reiserrob2003

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Brockton, MA.

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will .012 be enough or do I need more? I'm running 30% in Massachusetts.
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